Conference
in
Publication
3214
nternat,onal p on Laser nstrumentat,on ternationai Workshop Annapolis, Maryland May 18-22,1992 (NASA-CP-3214)
EIGHTH
INTERNATIONAL WORKSHOP RANGING INSTRUMENTATION 741 p
ON
LA3ER (NASA)
--THRU-N94-15552N94-15625 Unc|as
HI/19
0171410
!
=
ir
_rT q_[1,;.....................
;,-,,
.........
!!'!
i ii
= _,= ;_-:
::
iiiiii'_
, ......
, ...............
=
=l_r
i
_i
---
;_
NASA
Conference
Publication
3214
Eighth International Workshop on Laser Ranging Instrumentation
Compiled
and Edited
by
John J. Degnan Goddard
Space
Flight
Greenbelt,
Center
Maryland
National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 1993
Proceedings
of on
the
Laser
Eighth
International
Ranging
Annapolis,
Instrumentation Maryland,
May
18-22,
TABLE
Workshop
USA
1992
OF CONTENTS Page
Foreward
......................
•
No. . vii ,.,
List
of Participants
Workshop
.........................................
Agenda
vm
..........................................
xv
Scientific Applications and Measurements Requirements Laser Tracking for Vertical Control, P. Dunn et al., Hughes Laser Ranging NetwOrk Performance Determination at D-PAF, F.-H. Laser
Ranging
Satellite
Application
to Time
and to Other
Applications
ofSLR,
University
and Routine Orbit Massman et al., DGFI Transfer
Japanese
Space
B. E. Schutz,
Using
of Today's
Satellite
Greenwich
Laser
Observatory
Adaptive Median M. Paunonen,
Filtering Finnish
SATCOP
Planning
Laser
for Space
Mission
Ranging
et al.,
Research,
CRL
.....
1-34
..............
1-43
Royal Greenwich Graz ...............
Systems,
P.J.
Dunn
Obs .....
2-1 2-15
et al., 2-23
of Data
Distribution,
A.T.
Sinclair,
................................
for Preprocessing Geodetic Institute Software
Package,
2-34
of Time Series .......................... S. Bucey,
Measurements, 2-44
BFEC
..............
2-51
Technology
Nd: YLF Laser for Airborne/Spaceborne NASA/GSFC ............................................ Alternative
Wavelengths
for
New Methods of Generation et al., Czech Technical Simultaneously Train, An
1-19
of Texas
Hughes STX ........................................... SLR Data Screening," Location of Peak Royal
1-1
.................
H. Kunimori
Timely Issues Satellite Signatures in SLR Observations, G.M. Appleby, Work at Graz on Satellite Signatures, G. Kirchner, SLR The Precision
.............
Geodetic
Programs,
Center
STX
University
Xiangchun
Light
Source
Ranging,
Ranging,
J.L.
of the Passively et al., for
Shanghai
Laser
Ranging,
Dallas
et al., 3-1
K. Hamal,
Czech
of Ultrashort Laser Pulses for University ...............................
Compression
Yang
Improved
Laser
Laser
Mode-Locked Institute
Ranging,
Univ ......
3-7
H. Jelinkova 3-9
Pulsewidth
of Optics
K. Hamal
Technical
et al,
and
and Fine Czech
Pulse
Mechanics
. .
3-15
Technical
.............................................
3-19 iii PI_CEI:]_flG
PAGE
BLANK
NOT
FILMED
Epoch
and Event
Preliminary
Timing
Results
from
lntercomparison Detector
the Portable
Standard
with MOBLAS-7,
Satellite
Laser
et al.,
BFEC
M. Seldon
Ranging ................
Technology
Performance S. Cova
Optimization of Detector Electronics for Millimeter et al., Politecnico di Milano .............................
Tracking Capabilities of SPADs for Laser Ranging, Politecnico di Milano ...................................... How to Squeeze High Quantum A. Lacaita et al., Politecnico The Solid
State
Detector
Technology
for
Technical
Calibration
University
Ranging, 5-1
F. Zappa et al., 5-19
Picosecond
Laser
out of a SPAD, 5-25
Ranging,
I. Prochazka, 5-31
Atmospheric
T. Varghese et al., BFEC ................................... The First Satellite Laser Echoes Recorded on the Streak Czech
Laser
Efficiency and High Time Resolution di Milano ...........................
Czech Technical University .................................. Streak Camera Based SLR Receiver for Two Color
Measurements, 5-36
Camera,
K. Hamal
5-47
Techniques/Targets MTLRS#1
USSR
Campaign,
P. Sperber
Test Results
from
LAGEOS-2
Optical
Characterization
Using
Pulsed
T. Varghese et al., BFEC ................................... Analysis of TOPEX Laser Retroreflector Array Characteristics, MOBLAS
Multiwavelength
Syst6m
Characterization,
Ranging/Streak
Wavelengths
for
Two
V. Husson,
Atmospheric
U. Schreiber Millimeter
Color
TWo Wavelength Technical New
Dispersion
et al.,
Accuracy
Ranging,
J. Degnan,
Satellite
University
with WLRS
Fundamentalstation
Satellites
for
Laser
Wettzell
Two Color
Ranging
in Multiple
Data
State-of-the-Art
Analysis/Model
Using SPAD,
Lasers,
T. Varghese,
BFEC
6-33 6-47
BFEC
. . . ..........
6-59
NASA/GSFC 1.2m
.........
Telescope
7-1
Facility, 7-15
Wavelength
Mode, 7-28
J. Degnan,
NASA/GSFC
I. Prochazka
et al.,
. . .
7-36
Czech
......................................
7-52 Generation
Geodesic
Satellites, 7-56
Errors Laser
Range
Modeling
Applications, S.M. Klosko Geometric Analysis of Satellite
et al., Laser
Hughes Ranging
Improvement
Satellite
6-9
.....................
Ranging,
Perspectives for High Accuracy SLR with Second G. Lund, AEROSPATIALE ..................................
SLR
Mironov
Cameras
TWo Color Satellite Laser Ranging Upgrades at Goddard's T. Zagwodzki et al., NASA/GSFC ............................. Measuring
et al., 6-1
ETALON-1, -2 Center of Mass Correction and Array Reflectivity, N.T. et al., Main Astron. Obs. of the Academy of Sciences ..................
Optimum
et al.,
..................................
Experience and Results of the 1991 IfAG .................................................
Historical
4-1
of SLR Accuracy,
A Possible
for
Geodetic
and Oceanographic
STX ....................... Data, B. Conklin
New Step,
iv
M. Kasser,
et al., ESGT
BFEC .........
.....
8-1 8-15 8-23
Operational Software Developments On the Accuracy of ERS-1 Orbit Predictions,
R. Koenig
etal.,
DGFI
...........
9-1
Compensation for the Distortion in Satellite Laser Range Predictions Due to Varying Pulse Travel Times, M. Paunonen, Finnish Geodetic Institute .............. Timebias Corrections to Predictions, R. Wood Herstmonceux Castle ...................................... Formation Poisson
of On-Site Filtering
Normal
of Laser
Points,
Ranging
G.M. Data,
Appleby R.L.
Networking
NASADOSE Laser Ranging System McDonald Observatory ........... Operational
Lunar
Laser
A. Novotny,
Streamlining,
Application of the Robust Shanghai Observatory
et al.,
Ricldefs
Computer
Upgrade
Satellite
Laser
Ranger
Royal
etal.,
Czech
Greenwich
McDonald
Technical
Univ .......
Control Computers, .....................
D. Edge
etal.,
Estimate in SLR Data .....................................
BFEC
Obs...
Obs .....
R.L.
McDonald
x-y
Offset
Observatory
9-49
T. Detong
etal., 9-57
Guiding
Stage for
the MLRS,
P.J.
Shelus
et al.,
.....................................
LLR-Activities
in Wettzell,
Fixed
Upgrades/Developments
Station
U. Schreiber
Matera Laser Ranging Observatory BFEC ............................................... Performance
of the
Orroral
Geodetic Ranging
10-1
Upgraded Other
of Shanghai
Shanghai
Observatory
Status-Report
on WLRS,
Based
Research New
Laser
Xia
for
Laser
Technology
Upgrades/Developments Upgrades,
Results
of the MTLRS-1
Observatory
Luck,
G. Kirchner
Station,
etal.,
Space
SLR Graz
R. Eichinger
IfAG
Research 11-37
F.M.
Yang
et al.,
.......................
Location,
G.C.
11-51
Gilbreath
etal.,
Naval
Upgrade,
Receiving Transmitting Control
for Satellite
11-54
at Wuhan
P. Sperber
System, System,
System
et al.,
for
Geodesy
. . 11-31
11-44
Satellite
of Seismology
System
Based
J. Mck.
S. Schillak et al., ...........................
et al.,
Syslem
The new MTLRS
System,
11-6
in Graz,
Ranging
Satellite
TLRS-3
The new MTLRS#1
Ranging
...................................... Institute
10-14
et al.,
.................................
Mobile
Transputer
Laser
Improvements
R. Dassing
Ranging
et al.,
T. Varghese
.......
.....................................
of Ranging
Zhizhong
An Overview,
10-6
Wettzell
11-1
Satellite
Laboratory
Progress
Fundamentalstation
(MLRO);
Orroral
Observatory and
et al.,
of the Borowiec Laser Station, of Polish Academy of Sciences
Development
Ground
9-33 9-43
Lunar Laser Ranging Data Processing in a Unix/X Windows Environment, R.L. Ricldefs etal., McDonald Observatory ........................
Upgrading Center
9-26
Ricldefs
...............
Preprocessing,
9-19
Ranging
A Computer-Controlled
SUB-CM
9-9
Group, 9-13
Upgrading etal., HP
at SLR Stations,
etal.,
Laser
Ranging
........................
BFEC et al.,
11-60
.................... IfAG
Station,
12-1
.................
12-17
P. Sperber
et al.,
IfAG
...............
12-26
P. Sperber
et al.,
IfAG
...............
12-33
MTLRS,
E. Vermaat
..............................
V
et al.,
Kootwijk 12-40
Airborne
and Spaceborne
Airborne
2 Color
Systems
Ranging
Experiment,
P.S.
GLRS 2-Colour Retroreflector Target Design AEROSPATIALE ........................................ Effects
of Turbulence
NOAA
Wave
on the Geodynamic
Propagation
Millar
Ranging
Checkout
et al., Mars
Equipment
NASA/GSFC
Laser
Altimeter
J.H.
Chumside,
Spaceborne
13-33
(MOLA),
B.L.
Johnson
Systems,
J.C.
Jr. et al., 13-49
Laser
Altimeter
Smith
on a Single
13-52
Photon
Ranging
Technique,
University .............................. J.L. Burton, NASA/GSFC
I. Prochazka 13-74 13-78
...................
Presentations
Satellite
Laser
Station
University
Helwan
The Third
Generation
Performance
McGarry
Summaries
Scientific Timely
Cech
et al.,
No.
and
7836,
Speed
14-14
Microchannel
Space
et al.,
Flight
Plate
Station
Mobile
(GSFC)
Conference Business
1.2 Meter
........................
Ranging
Requirements
Sununary/Resolutions Workshop
14-29
...................
15-2 15-6 15-7
...........................
................................ ...............................
........................................
Upgrades/Developments
Telescope
15-5
Cameras
Upgrades/Developments
Meeting/Next
Tubes,
15-1
......................................
Ranging/Streak
System
Photomultiplier
14-20
Center
NASA/GSFC
and Measurements
Timing
et al.,
...................................
SLR Data Analysis/Model Errors Operational Software Developments Fixed
Systems,
H. Fischer
Detector Technology ........................................ Calibration Techniques/Targets .................................. Multiwavelength
TLRS
...............................
..........................................
and Event
Laser
Technical
14-2
.............................................
Technology
Lunar
Czech
.........................................
Applications Issues
Epoch
BFEC
on the Goddard
J.F.
Potsdam
of High
et al.,
Report
Session
M.
14-1
Potsdam
Comparison
T. Varghese Facility,
1992,
Upgrades, MOBLAS ...................................
SLR Station
GeoForschungsZentrum
Station
Status
.............................................
Optical Attenuation Mechanism R. Eichinger et al., BFEC
Laser
System,
...................................... Based
et al., Czech Technical Multi-Beam Laser Altimeter, Poster
for
13-1
G. Lurid,
............................
Development of the Mars Observer Laser Altimeter NASA/GSFC ..... ....................................... Bench
.........
Performance,
13-17
Laser
Laboratory
et al., NASA/GSFC
and Predicted
15-8 15-9 15-10 15-11 15-12 15-13
.............................. ............................
15-14 15-15
................................
16-1
...............................
17-1
vi
FOREWORD
At long last, As Chairman,
the Proceedings of the Eighth International Workshop are I tried very hard to obtain 100 percent of the presentations
"ready" for publication. in printed form so that
they could be distributed in these proceedings. In spite of the fact that the original submission deadline of 1 August 1992 was extended twice into early 1993 and numerous personal contacts were made, there are still several fine papers missing. Nevertheless, this volume contains the vast majority
of the presentations,
I desperately
wanted
workshop
to avoid
in Australia.
and I felt I could the embarrassment
Thank
publication these
any longer. proceedings
Besides, at the
1994
you to all who contributed.
One does not take on the job of chairing
a major
I wish
a number
to take
not delay of distributing
this opportunity
to thank
international
meeting
of people
who
without
made
a lot of help,
the Annapolis
and
meeting
a success. A special
thank
you
goes
to Miriam
Baltuck
and
Joe
provided funding support for the meeting. Not only overall success of the workshop, but it permitted greater
Engeln
at NASA
did this contribute participation from
Headquarters
who
substantially to the many of our foreign
colleagues. I alse
wish
to express
my thanks
to Karel
kindly offered his laboratory as a meeting to Ivan Prochazka for serving as unofficial also
to Program
their
busy
I am grateful papers include
Committee
schedules
members
and coming
Hamal
site for the Program recording secretary
Christian
to Prague
also for the support
Veillet
to help
of the session
and
plan
Thanks
also to Sarah
Wager
and Deborah
in selecting
the site for the meeting,
and general
coordinating
Last,
but certainly
during the entire itself (in countless
through
their
Committee in January during our deliberations. Ben
chairmen
who
for taking
1992, and Thanks time
were
responsible
from
for soliciting
presented in their sessions. Ben Greene, Tom Varghese,
of Westover
with hotel
and travel
I want to thank
my secretary,
Mrs.
effort - from mailing the initial ways), through the preparation
Consultants
for their
arrangements
final
distribution.
International
Workshop
I couldn't
have
done
it without
I. Degnan on Laser
Ranging
vii
Diana
Elben,
circulars, through of the proceedings
Chairman Eighth
Greene
who
These Jean
assistance
for the meeting,
activities.
not least,
support meeting
of Prague,
Georg Kirchner, Christian Veillet, Erik Vermaat, and Richard Eanes (for standing in on occasion).
Williams
helping
University
the workshop.
and for organizing and summarizing the material Bob Schutz, Andrew Sinclair, Helena Jelinkova,
Gaignebet, Karel Hamal, Ron Kolenkiewicz, Jim Abshire, Mike Pearlman, Carroll Alley,
John
of the Technical
Instrumentation
her.
for her wonderful supporting the for publication
8TH INTERNATIONAL WORKSHOP ON LASER RANGING INSTRUMENTATION MAY
James
Abshire
NASA/Goddard Code 924
Space Flight
Cntr.
Greenbelt, MD 20771 USA Phone: 301-286-2611 Robert
Greenbelt, USA
Space Flight
MD
20771
AI-Hussain
428-2 Ridge Road Greenbelt, MD 20770 USA Phone: 301-474-4787 Carroll Alley Department of Physics University of Maryland College Park, MD 20742 USA Phone: 301-405-6098 Fax:
30!-699-9195
OF
PARTICIPANTS
Wiard
Beek
Baltuck
NASA Headquarters Code SEP-05 Washington,
D.C.
Cntr.
Tammy Bertram NASA/Goddard Code 726.1
20541
Cntr.
Greenbelt, MD 20771 USA Phone: 301-286-8119 Fax: 301-286-2429
Spaziale
Jim Churnside
Space Flight
Cntr.
Brion Conklin BFEC 10210 Greenbelt Rd/Suite Seabrook, MD 20706 USA
Rd/Suite
700
Greenbelt, USA
MD
Space Flight 20771
Phone: 301-286-8591 Fax: 301-286-9200
.°,
Vlll
700
Phone: 301-794-3510 Fax: 301-794-3524
Seabrook, MD 20706 USA Phone: 301-794-3466 Fax: 301-794-3524
NASA/Goddard Code 920
NOAA - Wave Propagation R/E/WP1,325 Broadway Boulder, CO 80303 USA Phone: 303-497-6744 Fax: 303-497-6978
Greenbelt, MD 20771 USA Phone: 301-286-7052 Fax: 301-286-4943
Via Ospedale 72 Cagliari, 09124 ITALY
Boulevard
Lanham, MD 20782 USA Phone: 301-286-4076 Fax: 301-286-1620
John Bosworth
Steven Bucey BFEC 10210 Greenbelt
Jean Eugene Chabaudie Ave. Copernic Grasse, F06130 FRANCE Phone: 33-93-365869 Fax: 33-93-368963 Jack Cheek 4400 Forbes
Matera, 75100 ITALY Phone: 39-835-377209 Fax: 39-835-339005
Jack L. Bufton
39-70-72-5246
Space Flight
Giuseppe Bianco Centro di Geodesia P.O. Box 11
Cenci
via Tiburtina, Rome, 965 ITALY Phone: 39-640693861 Fax: 39-640693638
Apeldoorn, 7300 AN NETHERLANDS Phone: 31-5769-8212 Fax: 31-5769-1344
Aldo Banni
Phone:
Alberto
Kootwijk Observatory P.O. Box 581
NASA/Goddard Code 901
G.M. Appleby Royal Greenwich Observatory Madingley Road Cambridge, CB30EZ ENGLAND Phone: 44-223-37437 Fax: 44-223-374700 Miriam
LIST
Afzal
NASA/Goddard Code 924
Fahad
18 - 22, 1992
Sergio Cova p.z.a. Leonardo da Vinci Politecnico di Milano Cntr.
Milano, 20133 ITALY Phone: 39-2-23996103 Fax: 39-2-2367604
32
WilliamCrawford
Kenneth S. Emenheiser BFEC 10210 Greenbelt Rd/Suite
Seabrook, MD 20706 USA Phone: 301-794-3495 Fax: 301-794-3524
John J. Degnan NASA/Goddard Space Flight Cntr. Code 901 Greenbelt, MD 20771 USA Phone: 301-286-8470 Fax: 301-286-4943
Don Cresswell
Domenico
BFEC 10210 Greenbelt
Centro Spaziale Di Matera ITALY Phone: 39-835-334951 Fax: 39-835-3771
Joe Engeln NASA Headquarters Code SEP-05
BFEC 10210 Greenbelt
Rd/Suite
Rd/Suite
700
700
Seabrook, MD 20706 USA Phone: 301-794-3493 Fax: 301-794-3524 Henry A. Crooks BFEC 10210 Greenbelt Rd/Suite Seabrook, MD 20706 USA Phone: 301-794-3500 Fax: 301-794-3524
Howard Donovan BFEC 10210 Greenbelt Rd/Suite 700
Peter
Cntr.
Wettzell
David R. Edge BFEC 10210 Greenbelt
Rd/Suite
Winfield
Richard Eichinger BFEC 10210 Greenbelt Rd/Suite
Seabrook, MD 20706 USA Phone: 301-794-3474 Fax: 301-794-3524
Ave. Copemie Grasse, F06130 FRANCE Phone: 33-93-365849 Fax: 33-93-092613 Thomas
700
Fischetti
2609 Village Lane Silver Spring, MD 20906 USA Phone: 301-871-2425 Fax: 301-871-0269
Cntr. for Space Research University of Texas - Austin Austin, TX 78712-1085 USA Phone: 512-471-5573 Fax: 512-471-3570
Koetzting, 8493 GERMANY Phone: 49-9941-603112 Fax: 49-9941-603222
Rd/Suite
Feraudy
Eanes
Seabrook, MD 20706 USA Phone: 301-794-3474 Fax: 301-794-3524
M. Decker
Dominique CERGA
Dunn
Richard
Greenbelt, MD 20771 USA Phone: 301-286-6041
BFEC 10210 Greenbelt
700
Hughes STX 4400 Forbes Blvd. Lanham, MD 20905 Phone: 301-796-5036 Fax: 301-306-1010
Space Flight
Reiner Dassing Fundamental Station
Washington, D.C. 20541 Phone: 202-453-1725 Fax: 202-755-2552
Seabrook, MD 20706 USA Phone: 301-794-3491 Fax: 301-794-3524
E. Cuot Avenue Nicolas Copemic Grasse 06130, FRANCE Phone: 33-93-126270 Fax: 33-93-092615 Joseph Dallas NASA/Goddard Code 726.1
Del Rosso
700
Seabrook, MD 20706 USA Phone: 301-794-3495 Fax: 301-794-3524
Seabrook, MD 20706 USA Phone: 301-794-3508 Fax: 301-794-3524
ix
700
J.C. Gaignebet GRGS/CERGAIOCA Av Copernic Grasse, F06130 FRANCE Phone: 33-93-365899 Fax: 33-93-368963 Virgil F. Gardner NASA/Goddard Space Flight Code 901 Greenbelt, MD 20771 USA Phone: 301-286-8437 Fax: 301-286-4943 Luciano
700
Garramone
Centro Spaziale Di Matera ITALY Phone: 39-835-334951 Fax: 39-835-3771
Cntr.
G.C.Gilbreath Code 8133
Jean Louis Hatat GRGS/CERGA/OCA
Michel Kasser 18 Allee Jean Rostand
4555 Overlook Avenue, S.W. Washington, DC 20375 USA Phone: 202-767-2828 Fax: 202-767-1317
Avenue Nicolas Copernic Grasse 06130, FRANCE Phone: 33-93-126270 Fax: 33-93-092615
Evry Cedex, 91025 FRANCE Phone: 33-160780042 Fax: 33-160779699
Carl Gliniak
J. Michael Heinick BFEC 10210 Greenbelt Rd/Suite
Waldemar EER Systems Corporation 10289 Aerospace Road Seabrook, MD 20706 USA Phone: 301-306-7840 Fax: 301-577-7493 Ben Greene Electro Optic Systems 55A Monaro Street
Pty. Ltd.
Van S. Husson BFEC 10210 Greenbelt
Ludwig Grunwaldt Telegrafenberg A 17 Potsdam, 0-1561 GERMANY Phone: 37-331-0325 Fax: 37-332-2824
Seabrook, USA
Graz, A-8042 AUSTRIA Phone: 43-316-472231 Fax: 43-316-462678
of Sciences
MD
Rd/Suite
Steve
Helena
700
20706 Rol f Koenig DGFI
Jelinkova
Technical University Brehova 7
Frascati, 00044 ITALY Phone: 49-6-94180386 Fax: 49-6-94180361
of Prague
115 19 Prague 1 CZECHOSLOVAKIA Phone: 42-2-84-8840 Fax: 42-2-84-8840 of Prague
Seabrook, USA
MD
20706
301-794-3495
S. Jessie
NASA/Goddard Code 901
115 19 Prague I CZECHOSLOVAKIA Phone: 42-2-84-8840 Fax: 42-2-84-8840 William Hanrahan III BFEC 10210 Greenbelt Rd/Suite
Lawrence
Space Flight Cntr.
Ronald
Bert Johnson 700
Lebedev Physical Institute Russian Academy of Sciences Leninski Prospect Moscow, 53117924 RUSSIA Phone:
Greenbelt, MD 20771 USA Phone: 301-286-2052
NASA/Goddard Code 924
Marstallplatz 8 800 Munich 22 GERMANY Phone: 49-8153-281353 Fax: 49-8153-281207 Yuri Kokurin
Hamal
Technical University Brehova 7
Klosko
Hughes STX 4400 Forbes Blvd. Lanham, MD 20706 Phone: 301-794-5284 Fax: 301-306-1010
Phone: 301-794-3470 Fax: 301-794-3524
Paci Guido ESA/ESRIN via G. Galilei
Phone:
Feng Hesheng Chinese Academy
Georg Kirchner Lustbuhelstr 46
P.O. Box 110, Kunming Yunnan Province, PEOPLE'S REP. OF CHINA Phone: 86-0871-72946 Fax: 86-0871-71845
Queanbeyan, NSW 2820 AUSTRALIA Phone: 61-6-2992470 Fax: 61-6-2992477
Karel
700
Seabrook, MD 20706 USA Phone: 301-794-3469 Fax: 301-794-3524
Kielek
Warsaw University of Technology Faculty of Electronics Warsaw, 00667 POLAND Fax: 48-22255248
Space Flight
Greenbelt, MD 20771 USA Phone: 301-286-6179
Cntr.
7-95-132-7147 Kolenkiewicz
NASA/Goddard Code 926
Space Flight
Greenbelt, USA
20771
MD
Phone: 301-286-5372 Fax: 301-286-9200
Cntr.
DannyKrebs NASAIGoddard Space FlightCntr. Code726.1 Greenbelt, MD 20771 USA Phone:301-286-7714 HirooKunimori 4-2-1Nukui-Kita-Machi Koganei Tokyo,184 JAPAN Phone: 81-423-27-7560 Fax:81-423-21-9899 MauriceLaplanche
Grant Moule
Michael Maberry Institute for Astronomy P.O. Box 209
Electro Optic Systems 55A Monaro Street
Kula, HI 96790 USA Phone: 808-878-1215 Fax: 808-878-2862
Queanbeyan, NSW AUSTRALIA Phone: 61-6-2992470 Fax: 61-6-2992477
Paul Malitson BFEC 10210 Greenbelt
Alan Murdoch BFEC 10210 Greenbelt
Rd/Suite
700
Pty. Ltd.
Rd/Suite
Seabrook, MD 20706 USA Phone: 301-794-3505 Fax: 301-794-3524
Seabrook, MD 20706 USA Phone: 301-794-3497 Fax: 301-794-3524
Jean Francois CERGA/OCA
Reinhart
700
CERGA/OCA Ave. Copernic Grasse, F06130 FRANCE Phone: 33-93-426270 Fax: 33-93-092613
Franz-Heinrich
AUSLIG, P.O. Box 2 Belconnen, ACT 2616 AUSTRALIA Phone: 61-6-2357285 Fax: 61-6-2575883
Fax: 301-286-4943
Pty. Ltd.
Queanbeyan, NSW AUSTRALIA Phone: 61-6-2992470 Fax: 61-6-2992477
Aerospatiale CA/TO/I 100 Blvd, du Midi 06322 Cannes La Bocca FRANCE Phone: 33-9292-7856 Fax: 33-9292-7190
Pamela
Cntr.
2820
Millar
NASA/Goddard Code 924
Space Flight
Greenbelt, MD 20771 USA Phone: 301-286-3793 Fax: 301-286-2717 Joseph Miller 1130 Freeland
Road
Freeland, MD 21053 Phone: 410-357-5818
xi
Space Flight
Greenbelt, MD 20771 USA Phone: 301-286-9283 Fax: 301-286-4952
Timothy May Electro Optic Systems 55A Monaro Street
Lund
Jan McGarry NASA/Goddard Space Flight Code 901 Greenbelt, MD 20771 USA Phone: 301-286-5020
Carey Noli NASA/Goddard Code 935
Massmann
Pfarrangerweg 4 Petershalisen, D-8037 GERMANY Phone: 49-8137-5965 Fax: 49-8153-28-1207
John Luck
Neubert
Telegrafenberg A 17 Potsdam, 0-1561 GERMANY Phone: 37-331-0325 Fax: 37-332-2824
Ave. Copernic Grasse, F06130 FRANCE Phone: 33-93-365849 Fax: 33-93-092613
Dr. Kasimir Lapushka Riga SLR Station University of Riga Riga LATVIA
Glenn
Mangin
Cntr.
Antonin Novotny Technical University Brehova 7 115 19 Prague 1 CZECHOSLOVAKIA Phone: 42-2-84-8840 Fax: 42-2-84-8840
of Prague
Jacek Offierski P.O. Box 581 7300 An Apeldoorn NETHERLANDS Phone: 31-5769-8211 Fax: 31-5769-1344 Thomas Oldham BFEC 10210 Greenbelt
Rd/Suite
Seabrook, MD 20706 USA Phone: 301-794-3499 Fax: 301-794-3524
700
Cntr.
Klaus Otten P.O. Box 581
Francis Pierron OCA/CERGA
7300 An Apeldoom NETHERLANDS Phone: 31-5769-8211 Fax: 31-5769-1344
Ave N. Copemic Grasse, F06130 FRANCE Phone: 33-93-365849 Fax: 33-93-092613
Linda
Gary D. Robinson BFEC%CDSLR, Suite 750 10210 Greenbelt Road Seabrook, MD 20706 USA Phone: 301-794-3467 Fax: 301-794-3524
Pacini
NASA/Goddard Code 726
Space Flight
Norris Laboratory Ave.
Washington, D.C. 20375-5000 USA Phone: 202-767-2828 Fax: 202-767-1317
Jocelyn Paris CERGA Avenue Nicolas Copemic Grasse, 06130 FRANCE Phone: 33-93-126270 Fax: 33-93-092615 Kamoun Paul Le Rocazur, Rue Cntr.so Nice, 06100 FRANCE Phone: 33-92-92-7517 Fax: 33-92-92-7620 Matti Paunonen Ilmalankatu IA
E. Pop Sidlerstr.
5
Bern, 3012 PEOPLE'S REP. OF CHINA Phone: 4131658591 Fax: 4131653869
Technical University Brehova 7
of Prague
115 19 Prague 1 CZECHOSLOVAKIA Phone: 42-2-84-8840 Fax: 42-2-84-8840
Rd/Suite
700
Peter Pendlebury MOBLAS-5 Tracking P.O. Box 137 Dongara, 6525 AUSTRALIA Phone: 61-99-291011 Fax: 61-99-291060
Station
Randall
Stanislaw Schillak Astronomical Latitude Borowiec 91
Observ.
Komik, 62-035 POLAND Phone: 48-61-170187 Fax: 48-61-170219
Wettzell
Kotzting, Munich, 8493 GERMANY Phone: 49-9941603113 Fax: 49-9941-60322
Cntr. for Space Research University of Texas Austin, TX 78712 USA Phone: 512-471-4267 Fax: 512-471-3570 Bernard Seery NASA/Goddard Code 726
Street
Cambridge, MA 02138 USA Phone: 617-495-7481 Fax: 617-495-7105
5844 Five Oaks Pkwy St. Louis, MO 63128 Phone: 314-233-0421 Fax: 314-232-3393
Bob E. Schutz
Seabrook, MD 20706 USA Phone: 301-794-3478 Fax: 301-794-3524
R. Pearlman
J. Roessler
Ulrich Schreiber Fundamental Station
Ivan Prochazka
U.K. Rao BFEC 10210 Greenbelt
Helsinki, 00240 FINLAND Phone: 353-0-264994 Fax: 353-0-264995
SAO 60 Garden
James Pirozzoli Naval Research 4555 Overlook
Greenbelt, MD 20771 USA Phone: 301-286-4685
Michael
Cntr.
Ricklefs
Space Flight
McDonald Observatory University of Texas Austin, TX 78712-1083 USA Phone: 512-471-1342 Fax: 512-471-6016
Greenbelt, MD 20771 USA Phone: 301-286-8943
Giancarlo
Seabrook, MD 20706 USA Phone: 301-794-3494 Fax: 301-794-3524
Paul J. Seery BFEC 10210 Greenbelt
Ripamonti
p.z.a. Leonardo da Vinci Politecnico di Milano Milano, 20133 ITALY Phone: 39-2-23996103
xii
32
Rd/Suite
700
Cntr.
Michael BFEC 10210
Peter Sperber Fundamental Station
Selden Greenbelt
Rd/Suite
Selker
NASA/Goddard Code 726.1
Space Flight
Wettzeil
Koetzting, 8493 GERMANY Phone: 49-9941-603205 Fax: 49-9961-603222
700
Seabrook, MD 20706 USA Phone: 301-794-3499 Fax: 301-794-3524 Mark
Erik
Cntr.
Charles A. Steggerda BFEC 10210 Greenbelt Rd/Suite
Vermaat
Kootwijk Observatory P.O. Box 581 7300 An Apeldoom NETHERLANDS Phone: 31-5769-8211 Fax: 31-5769-1344
700
Huib Visser P.O. Box 155
Greenbelt, MD 20771 USA Phone: 301-286-1013
Seabrook, MD 20706 USA Phone: 301-794-3489 Fax: 301-794-3524
2600 AD Delft, NETHERLANDS Phone: 31-15-692160 Fax: 31-15-692111
Victor Shargorodsky Science Research Institute for Precision Device Engineering
Mark Torrence STX 4400 Forbes Boulevard
Thomas Varghese BFEC 10210 Greenbelt Rd/Suite
Lanham, MD 20706 USA Phone: 301-794-5213 Fax: 301-794-1010
Seabrook, MD 20706 USA Phone: 301-794-3498 Fax: 301-794-3524
J. Utzinger Sidlerstr. 5
Scott Wetzel BFEC 10210 Greenbelt Rd/Suite Seabrook, MD 20706 USA Phone: 301-794-3492 Fax: 301-794-3524
53, Aviamotornaya Street Moscow, 111024 RUSSIA Phone: 7-95-273-47-19 Fax: 7-95-273-19-37 Peter Shelus University of Texas at Austin Austin, TX 78712 USA Phone: 512-471-3339 Fax: 512-471-6016 Andrew
Berm, 3012 PEOPLE'S REP. OF CHINA Phone: 4131658591 Fax: 4131653869 M.R. van der Kraan P.O. Box 155 2600 AD Delft, NETHERLANDS Phone: 31-15-692269 Fax: 31-15-692111
T. Sinclair
Royal Greenwich Observatory Madingley Road Cambridge, CB30EZ ENGLAND Phone: 44-223-374741 Fax: 44-223-374700 David
Carolus Vanes P.O. Box 581
E. Smith
NASAIGoddard Space Flight Code 920 Greenbelt, MD 20771 USA Phone: 301-286-8671 Fax: 301-286-9200 Jay Smith NASA/Goddard Code 924
Space Flight
Greenbelt, MD 20771 USA Phone: 301-286-8525
Cntr.
Cntr.
Roger Wood Satellite Laser Ranging Herstmonceux Castle Hailsham, East Sussex ENGLAND Phone: 44-323-833888 Fax: 44-223-374700
700
700
Group BN271RP
7300 An Apeldoorn NETHERLANDS Phone: 31-5769-8211 Fax: 31-5769-1344
Yao Xingdia Changchun, PEOPLE'S REP. OF CHINA Phone: 0431-42859
Christian CERGA
Fu-Min Yang Shanghai Observatory 80NanDan Road
Veillet
Ave. Copernic Grasse, F06130 FRANCE Phone: 33-93-365869 Fax: 33-93-368963
,°o
Xlll
Shanghai, 200030 PEOPLE'S REP. OF CHINA Phone: 86-21-4386191 Fax: 86-21-4384618
WenweiYe WuhanSLRStation XiaoHongshan 430071 PEOPLE'S REP.OFCHINA Lu Yu-Lin Changchun, PEOPLE'S REP. OF CHINA Phone: 0431-42859 Xia Zhizhong Wuhan SLR Station Xiao Hongshan 430071 PEOPLE'S REP. OF CHINA Phone: 86-027-81342 Fax: 86-027-712989 Thomas Zagwodzki NASA/Goddard Space Flight Code 715 Greenbelt, USA
MD
Cntr.
20771
Phone:
301-286-5199
Ronald
Zane
University of Hawaii P.O. Box 209 Kula, HI 96790 USA Phone: 808-878-1215 Fax: 808-878-2862 Barbara STX
Zukowski
4400 Forbes Boulevard Lanham, MD 20706 USA Phone: 301-286-2779 Fax: 301-286-2929
xiv
WORKSHOP EIGHTH
AGENDA
INTERNATIONAL
WORKSHOP
ON LASER
Sunday
Evening,
6:00-10:00pm 8:00-10:00pm
May
RANGING
INSTRUMENTATION
17
Registration/Orientation Session
(Governor
Chairman
Meeting
Calvert
(Calvert
Inn)
Chamber,
Governor
Calvert
House)
Monday
Morning,
May
18
8:30-10:00am
Registration
(Joint
10:00-11:30am
Welcome/Orientation
Senate
- John
Welcome/IntroductionsWelcoming
Hearing
Room
Lobby)
Degnan
J. Degnan,
Address
- M. Baltuck,
Address
- J. Bosworth,
Program Head,
Chairman
Geodynamics
Branch,
NASA
Headquarters Welcoming
Manager,
NASA
Crustal
Project Orientation
- John Degnan
Last Minute Poster
Agenda
Papers
Submission
Schedule
Conference
Rooms/Splinter
Facilities Local GGAO
(A-V
Phone
for Proceedings Meetings
equipment,
Number
xerox,
for Workshop
Tour/Cruise
Restaurants/Local
- August
Attractions XV
etc.) Participants
1, 1992
Dynamics
Monday
Afternoon,
l:00-3:30pm
May
18
Scientific
Applications
Applications Texas
ofSLR,
SLR Tracking Richard
B. E. Schutz,
of Lageos
J. Fanes,
Center
of SLR to Gravity
Topography
Determination,
Tracking
for
Requirements
Center
and Etalon:
et al.,
Applications
Laser
Past Results
for Space
Field Modeling
Control,
Univ.
and Future
Trends,
Univ.
et al.,
P. Dunn
et al.,
Hughes
and Routine
LASSO Laser and
at the D-PAF,
Experiments, Ranging
Other
Laser
Application
Timely
Issues
- Andrew
Signatures
Greenwich
Earth
Orbit
et al., DGFI
OCA/CERGA
Transfer
Using
Programs,
Hiroo
TV Time
Transfer,
Geodetic
Kunimori
Satellite
et al.,
John McK.
CRL
Luck,
Sinclair
in SLR Data,
G. M. Appleby
et al.,
Royal
Observatory
Work at Graz Lustbuhel
on Satellite
SLR Data
Qualify
SLR Data
Screening
Greenwich
Signatures,
Control, for
P. Dunn
G. Kirschner,
et al.,
Normal
Points,
for
Preprocessing
Hughes
Observatory
STX
A. T. Sinclair,
Royal
Observatory Median
Measurements, SATCOP
for
STX
Observatory
Satellite
Adaptive
Veillet,
to Time
Space
Support
Performance
Ch. Reigber
Christian
Japanese
Ranging
Geodetic
Network
of Texas
NASA/GSFC
ERS-I
Ranging
Mission
Filtering
M. Paunonen, Planning
xvi
Finnish
Software
of
and Sea Surface
European
: Laser
Schutz
Research,
Research,
D. E. Smith
Vertical
for Space
- Bob
ESA's Intentions for Laser Tracking of Future Observation Satellites, Dr. Paci, ESA
Determination
4:00-6:00pm
& Measurements
of Time Series
Geodetic Package,
Institute S. Bucey,
BFEC
On'oral
Tuesday Morning, 8:30-10:30am
May
19
Laser
Technology
Nd: YLF Laser al.,
- Helena
Jelinkova
for Airborne/Spaceborne
Laser
Ranging,
J. L. Dallas
et
NASA/GSFC
Picosecond
Laser
Alternative
Wavelengths
Sci.
Transmitter,
and Physical
Laser
for
Jelinkova,
C. Veillet, Recent
Ranging,
Ranging,
Systems
K. Hamal,
J. Gaignebet,
of Ultrashort
of Nuc.
Ranging
Faculty
of Nuc.
Sci.
Laser
and Physical
to the Moon
OCA/CERGA Pulses for
Ranging,
H.
Engineering
and Meteosat3
at OCA LLR Station,
OCA/CERGA
Analyses
Geoscience
Laser
of Generation
Faculty
Multi-Pulse
Laser
QUANTA
Engineering
Two Color
New Methods
for
J. Ferrario,
and Laser
Laser
Oscillator
Ranging
System
Breadboard (GLRS),
Test Results
J. Gaignebet
for
the
et al.,
OCA/CERGA Simultaneous
11:00am-
12:00pm
Pulse
Train,
Epoch
and
Compression Yang
Event
Timing
Results of Accurate Lustbuhel Streak
Camera
Preliminary Intercomparison
Fu Min,
Results
Mode-locked
Shanghai
Observatory
Tests
Resolution,
from
Pulsewidth
and
- Ben Greene
Timing
Timing
of Passive
at Graz,
J. Gaignebet,
the Portable
with MOBLAS-7,
xvii
G. Kirchner,
Standard
M. Seldon
Observatory
OCA/CERGA Satellite et al.,
Laser
BFEC
Ranging
Tuesday
Afternoon,
1:30-3:30pm
May
19
Detector
Technology
Performance Ranging,
- Thomas
Optimization S. Cova
of Detector
et al.,
Tracking Capabilities Politecnico di Milano
Varghese
Politecnico
of SPADs
Electronics di Milano
for
Laser
for
Millimeter
(Invited
Ranging,
Talk)
F. Zappa
et at.,
How to Squeeze High Quantum Efficiency and High Temporal Resolution out ofa SPAD, A. Lacaita et al., Politecnico di Milano Solid
State Detector
Prochazka, Streak
Faculty
Camera
of Nuc.
Based
Atmospheric
Varghese
et al.,
BFEC
Temporal
Analysis
Sci.
of Picosecond
Faculty
of Nuc.
Sci.
Techniques/Targets
Experiences
and Results
P. Sperber
et al.,
(presented
and Physical System
and
System
Target
6:30pm
Buses
leave
7:00-10:00pm
Barbecue/tour
10:30pm
Observatory Buses return
High
Pulses
- Jean
of the MLTRS#1
I.
Accuracy
Measurements,
Reflected
T. K.
from
Satellites,
Engineering
Gaignebet USSR
Collocation
Campaign
Correction and Array Reflectivity, Astron. Obs. of the Ukrainian Acad.
of
by B. Schutz)
Characterization
NASA SLR Network V. Husson, BFEC New
for
Physical
Ranging,
Engineering
Delay
Laser
Test Results from LAGEOS-2 Optical Lasers, T. Varghese et al., BFEC Historical
Laser
IfAG
ETALON 1, 2 Center of Mass Nikolai Mironov et al., Main Science
Picosecond
Differential
Calibration
1991,
for
SLR Receive
Multiwavelength
K. Hamal, 4:00-6:00pm
Technology
Using
Concept
of the
of the NASA
Collocation
Based
for GGAO
Characterization
on Fizeau
Pulsed
SLR Network
and Special
Effect,
Using
Analysis
of the Techniques,
V. Shargorodsky
tour Goddard
(GGAO) to hotel
,°,
XVII1
Geophysical
and
Astronomical
Wednesday
Morning,
8:30-10:30am
May
20
Multiwavelength
Ranging/Streak
Two Color
Laser
Ranging:
Gaignebet,
OCA/CERGA
Optimum Wavelengths NASA/GSFC Two Color Telescope Two
Color
Laser
Ranging
Faculty
Satellite
of Nuc.
Millimeter Accuracy NASA/GSFC Low
Pulse
Faculty New
Spread
Ranging
Satellites
for
and
Possibilities
for
High
at Goddard's
Physical
1.2m
WLRS
Using
SPAD,
I. Prochazka
et
Engineering
Two
Retroreflector
J.
NASA/GSFC
U. Schreiber,
Physical
Sci.
Hamal
J. Degnan,
Upgrades
Sci. and
Laser
Ranging,
et al.,
Laser
of Nuc.
Satellites,
ll:00am-12:00pm
Ranging
at Wettzell,
- Karel
and New Developments,
Two Color
T. Zagwodzki
Two Wavelengths al.,
Potential
for
Satellite Facility,
Cameras
Color
Ranging,
Array,
J. Degnan,
I. Prochazka
et al.,
Engineering
Precision
2 Color
Ranging
to Geodesic
G. Lund
SLR
Data
Analysis/Model
State
of the Art SLR Data
SLR Modelling
Errors,
Errors Analysis
R. Eanes,
- Ronald
Kolenkiewicz
at GSFC,
S. Klosko,
Center
for Space
Hughes
Research,
STX
Univ.
of
Texas Geometric Analysis NASA/GSFC Improvement ESGT
of Satellite
of SLR Accuracy:
xix
Laser
Ranging
A Possible
Data,
New
Step,
J. Degnan
M. Kasser,
et al.,
Wednesday 1:30-4:00pm
Afternoon,
May
20
Operational
Software
On the Accuracy Compensation
of ERS-1 for
Due to Varying Institute Timebias
Developments
Pulse
Travel
Computer Technical
et al.,
Upgrade
Application Detong,
Laser
Roger
DGFI
Predictions
Finnish
Wood,
Operational
Geodetic
Satellite
Shanghai
Shelus
et al.,
Lunar
Laser
Environment,
Laser
LLR Activities Station
J.F.
Orroral
LLR
System University
- Christian X-Y
Ranging
Offset
Obs., Data
Ricklefs
in Wettzell,
Ranging
Mangin,
Antonin
Obs.,
Estimate
McDonald
Multi-Wavelength
Randall
Royal
L. Ricklefs
Novotny,
Control
et al.,
Czech
Computers,
of Texas
D. Edge
in SLR Data
et al.,
BFEC
Preprocessing,
T.
Observatory
Ranging
R.L.
G. Appleby,
Data,
Streamlining,
of the Robust
Laser
Points,
Ranging
McDonald
A Computer-Controlled
LLR,
Range
M. Paunonen,
at SLR Stations,
NASADOSE
Ricklefs
Lunar
Normal
of Laser Ranging Univ. of Texas
Networking Univ.
Upgrading
4:30-6:00pm
Laser
et al.,
Herstmonceux
Poisson Filtering McDonald Obs.,
HP
Times,
Kirchner R. Koenig
in Satellite
to Predictions,
The Formation of On-Site Greenwich Obs.
R.L.
Predictions,
the Distortion
Corrections
Ranger,
Orbit
- Georg
Veillet Guiding
University
Processing et al.,
Stage for
the MLRS,
in a Unix/X
McDonald
Obs.,
Windows University
Wettzell
Laser
et al.,
to the Moon
and METEOSAT
3 at OCA
Orroral
Obs.
J. McK.
XX
of Texas
U. Schreiber
OCA/CERGA
Activities,
P.J.
of Texas
Luck,
Geodetic
Ranging
Wednesday
Evening,
7:30-10:30pm Thursday
May
20
WEGENER/CSTG Morning,
8:30-10:30am
May
Meetings
21
Fixed
Station
Design al.,
Splinter
Upgrades/Developments
Principles
of Fully Automated
EOS Systems
Status
Luck,
Laser
(presented
Performance
Ranging
Upgraded
Geodetic
Upgrading of the Borowiec Research Center of Polish Progress
Hesheng,
Observatory,
Orroral
Laser
Improvements
B. Greene
G. Bianco
Ranging
in Graz,
et
et al.,
System,
J. McK.
G. Kirchner
Laser Station, S. Schillak Academy of Sciences
in the Work of the Yunnan
Yunnan
Development
Systems,
Obs.
Sub-CM Ranging and Other Laser Station Graz
New
Ranging
by T. Varghese)
of the
Orroral
Degnan
Inc.
of the Matera
ASI/CGS
- John
Laser
et al.,
Ranging
et al.,
Space
Station,
Feng
Observatory
of Shanghai
SLR Station,
Yang Fu Min,
Shanghai
Observatory WLRS
Status
Report,
NRL SLR Activities,
ll:00am-12:00pm
R. Dassing
and U.
C. Gilbreath,
NRL
Status
of Tokyo
Station,
Hiroo
Mobile
System
Upgrades/Developments
TLRS-3
System
Upgrades,
Results
of the MTLRS-1
R. Eichinger, Upgrade,
A Transputer Based Control Delft Uni_,. of Technology Presentation al.,
Kunimori,
of the Highly
ESGT
xxi
French
WLRS
CRL - Erik
Vermaat
BFEC
P. Sperber
@stem for
Mobile
Schreiber,
et al., IfAG
MTLRS,
E. Vermaat
SLR Station,
et al.,
F. P[erron
et
Thursday
Afternoon,
May
21
Airborne
l:30-4:00pm
and
Airborne
Laser/GPS
Krabill
et al.,
Airborne GLRS
Spaceborne
GLRS-R
- James
Abshire
of the Greenland
Ice Sheet,
W. B.
NASA/GSFC Ranging
Experiment,
B Extension
2 Color
Performance,
Studies,
Retroreflector
P.S.
Millar
K. Anderson, Target
et al.,
NASA/GSFC
GE/ASD
Design
and Predicted
G. Lund
Turbulence Churnside
Effects
Development al.,
Mapping
2 Color Phase
Systems
on the Geodynamic
of the Mars
Observer
Laser
Laser
Ranging
Altimeter,
System,
B.L.
J.H.
Johnson
et
NASA/GSFC
Bench Checkout C. Smith Single
Photon
Studies,
Equipment
Ranging
for
Spaceborne
Systems
I. Prochazka
et al.,
for
Faculty
Laser
Mars
Altimeter
Altimetry
of Nuc.
Systems,
and Atmospheric
Sci.
and Physical
Engineering Small
Spacecraft
Measurement Satellite
from
Operational
Altimeter
Low
to Satellite
Measurements, 4:00-6:00pm
Laser
Earth
Laser
Orbit,
Boarding
6:30-9:30pm
Conference
9:30pm
Return
Friday
Morning,
May
time
System
NASA/GSFC
Splinter
for Conference
Dinner
to Annapolis
Bufton,
et al.,
for
Meeting/Joint
LASSO Splinter Meeting/Arundel Poster Session/Governor Calvert 6:15pm
J.L.
Concepts
Ranging
J. Abshire Software
Instrument
for
NASA/GSFC
Lunar
Gravity
Hearing
Conference
10:30am-12:00pm
Business
Dinner
Cruise
(Annapolis
Cruise Harbor
12:00pm
Adjourn
Summary/Resolutions Meeting/Next
Workshop
xxii
Room
Room/Maryland Inn Inn/Calvert Chamber
22
8:30-10:00am
Topography
- Michael - Carroll
Pearlman Alley
Harbor)
J.
POSTER PRESENTATIONS
Satellite
Laser
Station
Helwan,
NRIAG,
Helwan,
Egypt,
and
Czech
Tech.
Univ.,
Prague,
Czechoslovakia 1.2 Meter
Telescope
Zagwodzki
et al.,
Ranging Plate
Data
Facility,
Space
Flight
Center,
Greenbelt,
Md.,
T. W.
NASA/GSFC
Quality
Photomultiplier
The Optical
Goddard
Attenuation
Improvement Tube,
from
T. Varghese
Mechanism,
High
Speed
et al.,
Detection
BFEC
R. Eichinger,
,,°
XXIII
BFEC
Using
6m
Core
Microchannel
Scientific
Applications and
Measurements
Requirements
N94-15553 LASER Peter
TRACKING Dunn
and
FOR Mark
VERTICAL
Torrence,
CONTROL Hughes
STX Corp.,Lanham,MD
Erricos Pavlis, Univ. of Maryland,College Park,MD Ron Kolenklewiez and David Smith, GSFC LTP,Greenbelt,MD ABSTRACT The since
Global
the
first
dimensional
Laser
Tracking
MERIT
Network
campaign
positlons
in late
stations very
when
to that small
predicted
effect.
measuring
the
we can
now
ranglng resolve
at monthly
data
accuracy
centimeter-level
intervals.
separately from the with a formal standard
of high
three
In this
analysis,
by recent
models
attention
component,
of post-glacial
must and
be applied
the
survey
the
horizontal components, error of 2 ram. using
The rate of change in the vertical can be resolved level of several geophysical effects. In comparing
Particular
vertical
and
LAGEOS
observatories considered stations
years of continuous observations. mm./year, which is at the expected in this
provided
1983
of participating
station height estimates have been can be determined by the strongest
of the
has
rebound, to data
observatlons
to a few the behavior
we find
and
survey
are
and eight
no
correlation
quality
critical
control
components
of
the geodynamle results. Seasonal patterns are observed in the heights of most stations, and possibility of secular motion at the level of several millimeters per year cannot be excluded. such motion must be considered in the interpretation of horizontal inter-slte measurements, can
help
to identify
seasonally
mechanisms
which
can
cause
variations
which
occur
linearly
with
the Any and
time,
or abruptly.
INTRODUCTION LAGEOS laser horizontal motion processes
and
ranging measurements at the observing stations
regional
deformation
movements are as large Island which lie astride ability
to measure
usually
been
independent
from annual as the network Accurate
processes allows loading
vertical
and the
to calibrate
the
stations.
of SLR
stations
altimeter
per work
year The
(Frey
and
Bosworth,1988).
fast moving stations boundary. The SLR to a few mm/year,
they time
significantly to our knowledge of helped to improve models of tectonic
boundaries
motions
because
variations.
directly grain
provide
of the
but
geodesic
horizontal
horizontal
control
can
of pre-
or
of post-glaclal The
scale
to establish instruments
assist
the
horizontal
post-selsmlc rebound
of an Earth-centered a global by determining
mission.
I-I
the
vertical the
radial
height
have
has
systems
component
et
tectonic
determination
can
Easter their
are
of atmospheric
system The
tectonic
averages (Smith have improved. in monitoring
Accurate
datum.
and
measurements
investigation
reference
lengths
rates
positioning
events. and
The
such as Huahine and data have demonstrated
values (Chrlstodoulldls et al., 1985) to quarterly has grown and observation and force models
detection
measurement
at the
network altimeter
in this
of vertical
progressed al., 1990)
at plate
as 17 cm/year between the Paciflc/Nacza plate
centimeter
used
have added and have
be defined
can
also
of the
orbit
also pressure in a
be employed of the
Degnan(1985) hasdescribedthe varioustechnicalmethodsof accuraterange which
include
as accurate bench-mark. points
we employ
in the
distance errors
that
range
the
and
laser
detection
scheme.
The
and
would
bias
the
magnitude
of the
the
final
center and be preserved
position and
returns
corrections
Errors station
in station
position,
is normally
distributed.
and
usually
normal
points,
yielding normal points with this system characteristic
signature
of the
would
satellite
We have between
time-keeping
although
round-trip
time
can
modern
degrade
systems
measurement
out in the horizontal directly affect their calibrated strict
quality
Figure
control
1, and
component.
their The
network,
standards.
The
positions
listed
observations
from
determination of 3-dimensional improved resolution of the rate DATA ANALYSIS
In our satellite squares
analysis,
model
subsequently positions, motion
each
over
of mass al., 1992)
about and
the
The
time
more
have
locations
array
range with on
the
photon, leading edge detection methods may
of the transfer
difficult
subjected
of these 1, with
strong
measurement
of equations (Putney, 1990) spans
horizontal
stations
of
are
They
will
observations are
shown
allow
of a year
tend
sky coverage, our analysis
emphasis
now
time
at the level of positioning model. Systematic errors
their
stations
component
for epoch
to control.
particular
in
to cancel
but will to the best
to particularly on
on
the
the
world
map
of
vertical
us to reduce to a month,
with
expanded
an
the and
interval thus
for
provide
effects
of thermal
effect
(Rublncam,
(Ries
value
of a numerically
integrated
range Information in a least computed with an accurate
The
on the with
frame
from
satellite an
I-2
initial
which
resulting
Includes
of 398600.4415
et ai.,1992).
to Include
perturbations
1990)
solution
a month.
in a reference
tides
drag
the
linear
system
is
three-dimenslonal coordinates of the tracking station parameters estimated at various tlme Intervals. The
adopted
constant ocean
constrains
which satisfies all of the for orbits independently
of approximately
is computed Earth
supplemented by third body Mercury through Neptune.
Yarkovsky
by
a longer will vary
retro-reflector
of stations with adequate treatment we have restricted
and
these
resolution
GPS
positions from a quarter of any station movement.
SLR
time
gravitational
with
be causecl
adopted a value of 251 ram. the satellite's center-of-mass
insignificant error satellite perturbation
are
in Table
solved to yield monthly together with other geodetic
of the satellite
relativity
be
Any
METHOD
trajectory. A system sense is developed
perturbation
is an in the
for range
in the
the
using
position measurements height estimates. In this
observatories
must
by a few millimeters.
synchronized to the microsecond, which accuracy currently dominated by errors the
for the
system
return, although
also depend on the instrument. for the correction for the offset
differing
a ground in the normal
estimates
detection
and its reflecting surface, which would be expected from the multiple detection MOBLAS systems. Lower power transmitters with alternative require
m_surement refraction, as well
atmospheric
transmitter
of satellite
which would delay the detection of the than that from a Gausslan distribution,
range measurement will (Fitzmaurice et al., 1977)
delays
will affect
instrument's
distribution
pattern
path
between a system's electro-optical in the original observations will
analysis,
of each
to ensure
skewness
for electronic
in our
Characteristics
monitored errors value
calibration
surveys of the Any systematic
which
stations.
the
careful
The
significant the
were
sun
GEM-T3 the
perturbations moon,
represented
satellite
spin
effect
together
by a model axis
of general
for GM,
geopotentlal
LAGEOS and
the
km3/sec2
orientation
the
model
product (Lerch
et
was with
of the
the
planets
Earth
of 22 degrees,
decreasing by 50% every 6 years. To satisfy remaining track acceleration was adjusted every 15 days, as well track
component
acting
once
parameter been found
is related to the to accommodate
adequately
described
determined
by the
determined
parameter
repeating (Anselmo
(cf. Eanes with
the
same
measures
position
dynamics
The
radiation
the
value.
The
values
unusual
than
this
could
vertical
components
loading
at appropriate
this semi-diurnal of stations with
at favored
of the
times
locations
function variation
in it's
in 1991,
and
of the
day
(or night).
International
Earth
Rotation
Service
was
workers on both
crossing
associated
with
indicates
a have
The
once
per
revolution
level
Standards:
each
month.
McCarthy,
1991),
averaged over the monthly have an effect on stations and
for one
shown
have suggested that would lead to chaotic spin
by as much as ten 3, the root mean square fit of precision it is possible to
(IERS
rotation
of
equator
observations
centimeter
were adjusted included, and fixed
amplitude
results.
at the
applied
Earth
in which they polar motion
is a well-
regularly
signature
from those
recent
Iess(1991) gradient
these
stations
angle
particularly
effect would be very small when adequate sky coverage, but would
were taken from a global solution system with the effects of dynamic
the
along-track
of orbital
plane,
explain
was
2. This
and
models.
Bertotti and and gravity
selected
acceleration
in Figure
of the
has
of the once-per revolution acceleration the direct effect, and have formal errors
again
help
alongalong-
adjustment
along-track
is shown
behavior
unusual and
revolution
1 plcometer/scc2,
by these
continues in 1992. due to eddy currents and
per
have been modelled by several et al., 1991) using theories based
equatorial
The
in 1989
effects, a secular amplitude of an
by Yoder et al.(1983) and which have not yet been
of secular period
cosine
in the
pressure.
1992,
once
affect monthly orbital fits to the ranging observations but when modelled according to the values of Figure data remains below five centimeters, and with this
Ocean although estimates
or
The
components determined
behavior
This
of about.
predicted
perturbations
satellite's
in 1991
perturbations centimeters, each month's
by the
orbit.
experimental
uncertainty
well
as a typical
that the irregular behavior torques on the spacecraR
track
the
heating.
very
the orthogonal more weakly
size and
in the
solar
is not
unmodelled
resolve
over
a formal
direct
in 1990
Figure 3 shows estimates, which are
change
of the
orbit and
excitation vector described in the behavior of LAGEOS
et al., 1991).
full network
and
commencing
solar
revolution
patterns in the early part of the signature et al., 1983; Afonso et al., 1989; Scharoo
Earth-reflected
about
per
eccentricity variations
unmodelled as the phase
orientation
parameters
daily in the J2000 in which the UT1 day
of each
position which
month
(EOP)
reference time published to establish
a
longitude frame. In the global solution the station position for each site was estimated, motion was modelled according to Smith et al.(1990), resulting in a consistent reference
but its frame
throughout the eight year experimental period. In both the monthly analysis which yielded the height values presented
the system
was set by fixing the horizontal position Maul (latitude). The results for monthly both of the flducial stations at Greenbelt and
if there
were
Wahr(1981) according LASER
DATA
and
from
the
components of Greenbelt (latitude and longitudes) and values of station height are reported only if coverage for and Maul reached a minimum of nine LAGEOS passes, each
effect
solution for EOP and the stations' reference
individual
of solid
station.
Earth
tides
A nutatlon at the
series
stations
was
according
to
also
computed
analysis
contains
1981)
QUALITY
of the
calibrated
data
adopted
to Wahr(
Each well
was
adequate
global here,
CONTROL
observatories system
that
whose has
been
vertical
motion
in operation
1-3
since
was late
monitored 1983.
In this During
the
lifetime
of each
a
station, continuous improvements are made to the system through up-grades in hardware and software. Any disturbance at an instrument is monitored with accurate resurveys of the system's eccentricity
(optical
in the surveyed eccentricity Center
center
offsets
are
respect
of the
in Table
System
tower
MOBLAS
2. They
(CDDIS)
to an associated
calibration
for the various
listed
Information
with
distance
have
ground
used
instruments
been
in December
from
and
their
as well
delay
fielded
retrieved 1991
marker)
for system
as of any change
correction.
The
by the Goddard
the Crustal
Space
Dynamics
correctness
will
Flight
Data
directly
affect
the
estimated heights given in Table 1, as well as any measure of vertical motion. The remaining observatories in the network were assumed stationary during the eight year period and their positions refer to the optical axis of each telescope, which is the estimated parameter in our reduction. the
Any
marker
improved
information
positions,
and
on eccentricity
it is not necessary
to repeat
other hand, techniques for direct estimation values at the outset of the analysis to connect Information
concerning
calibration
by subsequent
improvements
might
analysis,
exert
bias
parameters,
and
updates using linear shiRs the initial time-consuming
to efficiently
reduction
process.
On the
require accurate eccentricity occupation at a site.
system
is accessible
through
the
to compensate
position.
Subtle
of our
for any effects
engineering
problems
using the original by pass-by-pass
analysis
facilitates
based on the partial derivatives computation of normal equations.
retro-actlve
time-of-flight observations, or longer term range or
the
of range Several
that
in the detection
incorporation
of historical
or clock bias computed in corrections to the released
data were required. In particular, range corrections cm to each measurement up to March 1986 to allow
to Arequlpa observations for the improved survey
were applied: of the calibration
tower
noted
as well
until
which
time
Range
errors
in the CDDIS improved of this
description
system
delay
magnitude
of this
would
of a few ram/year,
is closely
monitored.
The
an abrupt
change
when
earlier,
frame
of Figure
year
data
earlier
in station
span,
observations
ANALYSIS
The month
independent
variation
the vertical
estimates
In our
and
force, laser
of several
measurement
analysis from
of height are given
an average
the measurements
ranges
centimeters and
is modelled
in quarterly
solutions
bias
held
fixed
shown
at the
was
motion locations
position
clearly
shown
is
seen
in the
estimated
4 indicate
at
1988).
at other
in station
this
at a value
in Figure
Earth
In amplitude
are models.
to Marini
1-4
and
stations 5a,b
with
and
semi-major
are qualified
orientation
according
three
in Figures Earth
standard deviation based on the final fit of the range the ranges themselves are formally accurate to better signatures
level:
1988
lower
over
error
the
13
in the
magnitude.
values
of the distance scale
of range
anomalies effects
July
(Husson,
of vertical
of similar
maintained was
offset
any estimates
of engineering
used
3 cm
this
4
MEASUREMENTS
monthly
seen
was
of the station
of the correct
OF VERTICAL
in millimeters
data
the height
the monthly
affect
indication
as another
Indicated
the possibility
to a subsequently
Arequipa
4. When
and
compelling
height
uncorrected
procedures
significantly
at the rate
most
station,
calibration
occurring
data
up-date
in the processing of the raw range measurements As corrections to the calibration procedures are
it is necessary
the design
be used
full data
of each
system must be remedied in a pre-processlng stage but many of the data corrections can be represented timing
the
characteristics
on station
can
of station velocity will the positions of each
CDDIS, although it is has already been used and is thus embedded in the normal points. uncovered
surveys
c. The
axis
by error
the
lowest
least
significant
of 6378136.3
estimates
The Murray
due
effect
of twice
to uncompensated
of atmospheric
(1973)
who
assumed
figures
m. appear
observations to each orbital than a centimeter, systematic
observed
month-to
their
formal
arc. Although residual errors
refraction
In on
a spherically
the
on
stratified
atmosphere
based
on surface
range corrections due the refractivity dependence of the range correction elevation variations
angle, which is the in station barometer
pressure
measurements.
formula, the formula should
lower limit accuracy
zenith only
Herring
(1988)
not
be separable
The
possibility
for stations Huahine collocation
which
from
the wet
for most of the systems. However, or in the effects of lateral gradients
of errors
in the
have
undergone
component
in nearby
adopted
of system
must
The
collocation
transportable
calibration
working TLRS-2
location. eccentricity
likely
Considerable and
to their
quoted
individual
most
values
listed
in Table
height
statistic
component
1 are has
only
reduced
been
of motion
used
(see,
a mean we see
as upon
the
of the
precision and
Arequipa
Post-glacial
observations,
of the
and reliability
of the
Earth
from
factor
in earlier
lower
for some
significant
compared
on the
fit of the
about
the
fit is substituted. measuring
of height
the
horizontal scatter
'quality' careful
scatter
mean The
the
Considering
as a measure of the system stability and values
melting
variation
values
work
et al., 1990).
of these
the
a linear
and at their
sites but, because technique, this
based
height
test
MOBLAS-1
not
error
when
the
and
for up-grades
height
3 are
or two
3 of Smith
to the
accurate
standard
(or uniformly moving) value that it depends as much on
testify
rebound
control
Table
Quincy
a collocation
in the
in Table
of scatter
by a millimeter
less
be noted
formal
particularly
Greenbelt,
to Greenbelt undergo
early,
shown the
measures
as a quality
height about performance,
can
rates twice
The
for example
station's station's
Yarragadee
are
line.
of the
motion
height
which
to a straight
influence
uniform
estimated
uncertainties,
usually
could
sites coincided with machine as well as its
returned
do not
as
shows more variation than the other by employing a precise reposltionlng
to the
from
of the
periodically but
position minimized
to be due
deviation
are
MOBLAS-7,
The Huahine errors are
behavior is more measurements.
stations,
systems
against
be considered,
such
American ranging
any long term in the atmosphere
instruments.
also
occupation,
(see Table 2). The system changes at the North tests which cross-calibrated each instrument's
eccentricity.
that
The SLR systems refraction which
microwave
eccentricities
changes
shown
range correction and the elevation be a few millimeters at 20 degree
(see Abshire and Gardner, 1985) will directly affect the vertical estimates. thus be used to monitor aberrations in the dry component of atmospheric would
has
of a
of the calibration
at Greenbelt,
instruments. of continental
ice sheets
starting
roughly
18,000 years ago produces changes in the gravity field as it affects the long-term evolution of the LAGEOS orbit and have been reported by Yoder et al. (1983) and Rubincam (1984). Wagner and McAdoo due
(1986)
present
to post-glacial
complete
enough
predicted
by the
compared
the
for convenience and observed
model
model
nor
America due could
the
observations
lack
explain
modelling observations,
SLR
sites.
taken
from
height
detection
the
by tide model
rates
model
maps The
for the
rate
of Wu and
values
Figure
of vertical
from
the
gauge
results.
data
in their James
of the
at Greenbelt (see
Trupin
treatment and
1-5
uplift and
laser
1991) been
(1990)
lithosphere horizontal
: the
absence
noted have
data
sinking
at each from
other
position model
is
observatory and
the
SLR
are
stations,
between the rate expected hand,
of eastern of higher
by Wagner shown
this
McAdoo(1986)
On the
confirm
of radial and
can be seen the 4 mm/year
systems.
can has
Morgan
of the properties of the have also indicated that
SLR
of change
Peltier(1983),
5 of Wagner
estimated
capability taken
of a lithosphere
assumptions and they
Ice-2
by tectonic plate. Very little correlation values of up-lift, even in Europe, where
the
as required
to the
viscosity
the
been
the
is within SLR
on
all the
have
3 with
uniform
based
to include model
in Table
arranged modelled
a simple
rebound
and
in more
neither
from the
North degree
terms
McAdoo detail
and
how
can cause disagreement with sea level motions due to post-glacial rebound in
North America
and
Fennoscandia
can
amount
to 4 mm/year
from
plausible
models.
This
movement is predicted 10 ram/year, and both
in the Hudson Bay region where vertical movement can amount to over components are clearly within the resolution capability of a modern SLR
system
this
region
in an extended
that
further
investigation
occupying
It is possible instrument
error
apparent assume
which
would
rate, of 4 mm/year a stationary
alias
of the
into
observed
vertical
campaign. SLR
the vertical
at Arequipa
component
and
observations
will
component Is large
expect
uncover
of station
enough
accurate
that
baseline
stations. Only explicit separation from the vertical component will allow the definition of accurate horizontal motion.
a source
tx_sition.
no SLR
analysis
measurements
by considering
of
However,
the
should to distant
geodesic
lengths
CONCLUSIONS
The eight
stability
year
analysis
time does
signatures nature,
of the span
height can positioning campaigns exercised
that
in the height
of position
vertical
variations
do not produce
motion
suggested results
significant
represent
term
in close to retain
proximity
to the SLR
the full scaling
as they benefit from tracked. On the other
reception
center
from
strong hand,
orbital accurate
supplemented resolution
These
a ground
marker
to be in high
Earth
orbit
by concentrated of any subtle
vertical
in the next
tracking motion
1-6
variations
also
this
of a geophysical
estimates
of station
as to establish scale for on a global scale, such as GPS quality
control
which
is not so stringent
in both
space
As observations orbiting
be improved.
ETALON
from
techniques
be
are of each and
Network can satellites
LAGEOS
spacecraft,
must
in the analysis
when multiple satellites position measurements
is critical
few years.
in an
Periodic
which the Global Laser Tracking number of retro-reflector-carrylng
of the currently should
and
rebound.
accurate
ranges
geometry relative
observatories
by 2 or 3 ram/year
The data
of the laser
SLR
of post-glacial seasonal
trends.
Observatories.
accuracy
must be carefully monitored. The capability with control vertical scale will grow with the increased expected
strongest
Is bounded
by models
may long
at the
help in the calibration of satellite altimeters as well tech'niques which degrade as a function of distance
of GPS networks simultaneously instrument's
component
suggests
not confirm
apparent but
radial
2 are time
REFERENCES
Abshire,J.B. IEEE Trans.
Afonso,
and C.S.Gardner,"Atmospherlc on Geose. and Rem. Sense.
Refractivity GE-23, 1985
G,F.Barlier,M.Carplno,P.Farlnella,F.Mignard,M.Milanl
LAGEOS
Seasons
and
Eclipses",
Pressure
for a Spacecraft
Bertotti,B.,and
L.less,"The
Chrlstodoulidis,D.C.,
D.E.Smith,
P.J.Dunn,"Observing J.Geophys.Res.,
90(B
Degnan,J.J.,"Satellite Geose. and Rem.
Eanes,R.J.
and
Ranging
M.M.
of LAGEOS",
Laser Ranging: GE-23, 1985
Fltzmaurice,M.W.,P.O.Minott,J.B.Abshire Geodynamic Satellite (LAGEOS)",
NASA
Frey H.V. and J.M.Bosworth,"Measurlng Dynamics Project", Earthqu. and Volc.
Six Month
James,T.S.,and 1990
NASA
Goddard
Space
Coefficient
and
Syrup.
Flight
and of the
IERS
Adv.
in press,
i-7
Testing
Motions:
Report,
1992
Res.,
IEEE
Trans.
Field
from
of the
Laser
NASA's
October Rebound",
Tracking, Altimeter 104555, 1992
Note
3, Central
I0(3), in the
Ranging",
on
Satellite
1991
M.H.Torrence,"Preclslon Space
Laser
Gravitational
to Post-Glacial
Tech.
to Radiation
and
Prospects",
Crustal
due
M.M.Watkins,"Progress
Earth",
of
1991
Satellite
No.3,Vlenna,
Report",BFEC
and Center",
from
H.E.Rowe,"Prelaunch Paper 1062,1977
Contemporary 20(3), 1988
due
M.H.Torrence
Future
Models of the Earth from Satellite GEM-T3 and GEM-T3S", NASA TM
Ries,J.C.,R.J.Eanes,C.K.Shum Gravitational
and Tech.
D.D.(ed.), IERS Standards(1989), de Paris, 1989
Effects
96,2431-2440,
of Earth's
IUGG
Motions
Putney,B.,R.Kolenkiewlcz,D.Smith,P.Dunn the
Ass.
Orbital
Perturbations
Deformations
Status
Processing
W.J.Morgan,'Horizontal
Lerch,F.J," Geopotential Gravity Observations: McCarthy Observatoire
Data
and
Variability
XX Gen.
Ranging",
29,27,1983
S.M.Klosko,
Current
Watkins,"Temporal
Mech.
J.Geophys.Res.,
R.Kolenkiewicz,
Observations",
Husson,V.S.,"First
Celest.
Tectonic Plate Motions 1 I),9249-9263,1985
Sense.
A.M.Noblli,'Orbital
Shape",
Rotation
A.M..Nobill,"
Laser
7(5),501-514,1989
and
of Complex
in Satellite
and
Ann.Geophys.A
Anselmo,L.,B.Bertotti,P.Farinella,A.Milani
Laser
Corrections
197-203,
Crustal
1988 Geo.
and
R.Lett.
Surface
Bureau
of IERS,
Orbit
Determination
1990
Determination
17(7)
of the
at
Rubincam,D.P.,"Postglacial Lower
Mantle",
Rublncam
Rebound
J.Geophys.Res.,
D.P.,"Drag
on
Observed
89(B2),
the
LAGEOS
Satellite",
and
J.Geophys.Res.,
95(B
R.Noomen,"On
96,729-740,
Trupin A.S.," Gravitational
Wagner,C.A. Intersatellite
13),22013-22041,
The Effect Potential",
Forced
Geophys.J.R.Astron.Soc.64, Wu,
P.,and
Constraint
Deep
303,
Long 1991
Variation s. 91(B8),
95,4881-4886,1990 the
Along-track
Satellite
Period
Acceleration
of the
and Ranging to LAGEOS",
Laser
Tides
In the Earth's July, 1986
of an Ellipsoidal
Glacial
Mantle
Isostatic
Viscosity",
on
the
Gravity
Rotating,
Adjustment Geophys.
Yoder,C.F.,J.G.Williams,J.O.Dickey,B.E.Schutz,R.J.Eanes Earth's Gravitational J2 Coefficient from Nature
of the
Earth's
Elastic
Field
and
Rotation
Detectable
Oceanless
and
With
GRM
Earth",
1981
Peltier,W.P.," on
Viscosity
1991
of Global Change and U. Col. Ph.D. Thesis,
Nutatlons
Effective
1990
and McAdoo,D.C.,"Time Traeking_,J.Geophys.Re
Wahr,J.M.,"The
the
Geophys.Res.,
Smith,D.E.,R.Kolenkiewicz,P.J.Dunn,J.W.Robbins,M.H.Torrence,S.M.Klosko R.G.Williamson,"Tectonic Motion and Deformation from J.Geophys.Res.,
and
1984
Satellite",J.
Scharoo,R.,K.F.Wakker,B.A.C.Ambroslus LAGEOS
by LAGEOS
1077-1087,
LAGEOS
1983
I-8
and
the
J. R. Astron.
and
Free
Air Gravity
Soc.74,
Anomaly
as a
1983
and B.D.Tapley,"Secular Non-tidal Acceleration
Variation of of Earth Rotation",
TABLE
1 :
STATION
POSITIONS
LATITUDE DEG
MNSEC
LONGITUDE
HEIGHT
ST.ERR.
DEG
METERS
MILLIMETERS
MNSEC
ST.DEV
NO. MONTHS
283
i0 20
19.931
2
16
69
30
239
3 19
1107.119
2
18
67
32
53 30
243
34
39
1839.746
2
20
73
7090
-29
2 47
115
20 48
242.080
2
16
69
HUAHINE
7123
-16
44
l
208
57 32
46.110
5
23
22
AREQUIPA
7907
-16
27
57
288
30 25
2492.945
2
17
52
MATERA
7939
40 38
56
17
536.551
2
19
60
WETZEL
7834
49
12 52 41
661.842
4
24
45
GRAZ
7839
4742
15 29 36
540.125
3
20
55
RGO
7840
50 52
76.114
3
21
69
SIMOSAT0
7838
33 34 40
100.175
4
25
51
GREENBELT
7105
39
114
QUINCY
7109
39 58
MON.PEAK
7110
YARAGADEE
8 42
16 42
20
3 135
I0 56
13
I-9
TABLE
2 : ECCENTRICITY
OFFSETS START
GREENBELT
7105
QUINCY
MON.PEAK
MOBLAS-7
GROUND
1
1
84
3 22
16
-26
3169
84
3 22
85
7 29
17
-32
3169
85
7 29
89
10 12
17
-31
3168
89
10 12
90
7 25
35
-40
3162
90
7 25
91
12 31
-14
-33
3153
4
6
90
7 23
-7
-5
2613
TLRS-4
90
7109
MOBLAS-8
84
I
l
86
9 18
-29
11
3124
86
9 26
91
3 17
-27
12
3138
TLRS-4
91
3 19
91
8 19
-5
0
2651
MOBLAS-8
91
l l 18
91
12
II
-19
5
3184
91
12
12
91
12 31
-35
-3
3184
7090
MOBLAS-4
841
TO 7918
7121
TO 7123
MOBLAS-5
7121
MOBLAS-
7123
TLRS-2
MARKER
7105
UP(mm)
84
1
88
4 30
-33
-15
3210
4 30
91
12 31
-33
-16
3213
84
1
87
8 13
87
813
91
12 31
3 3
11 10
3185 3177
88
HUAHINE
N(mm)E(mm)
7918
71 I0
YARAGADEE
STOP
I
1
84
l
1
86
3 13
8
I
3662
87
7 14
87
10
8
0
0
1453
88
3 16
88
9
I
0
0
1437
89
424
89
9
3
0
0
1482
90
3 15
90
8 20
-I
3
1459
91
4
91
9
-2
4
1482
5
DISTANCES X(mm) -14419 1458
Y(mm) 5137
Z(mm) 9457
807
501
i-I0
4
TABLE TECTONIC
3 : COMPARISON
PLATE
N. AMERICAN
STATION
WITH
POST-GLACIAL
REBOUND OBSERVED
MODEL
GREENBELT
3
1.7
QUINCY
3
1.5
MON.PEAK
I
2.6
2
HUAHINE
I
3.2
4
AFRICAN
MATERA
I
2.3
EURASIAN
WETZEL
4
- 1.5
3
GRAZ RGO
4 4
.9 -.2
2
AUSTRO-INDIAN
YARAGADEE
I
1.4
2
S. AMERICAN
AREQUIPA
-2
4. l
2
UNKNOWN
SIMOSATO
-3
2.2
4
PACIFIC
MODEL
I-II
+b2 mm/year 2
2
2
0 0
>.
_o
0
"I" Q. .Q r-
O"
-
i |
8 8 $|1
>-
'OO O"
e e
I el I
cO OR
e,,,,-,
ee
I, I 0
i
e e e e I
e
("4 CO O"
e
|° 01
0
i e I
i' ,i'
C) 'CO O-
t
|
I
i
Ii
:
e
i,', : O
!
0 U")
i
I
I
I
I
I
e
_
I
'i
e
lllllllll
I (:D
CO r-OO"O
(LUO) S_B AInU OIAI
1-15
0 ..............................................
+ ............
_.._
.............................................
I C I_
0 0
I=.
m MH
0
i
0 o.
L
J l In /'_zl
0 0
0 0
0 0
0 0
0 0
(s,e),Om!ll!m) ),q6!eH 1-16
0 0
C_ O_
_IHH
HHi '
i k.
O_ _lm'
CO 0
.C
......................................................... _ ""............................................. CO
4)
0
>, h4_
............................................................... ,.._._ ............................................. r,,, !
O
a_
2 .j I
:
O U)
CO
0
0
0
0
0
(_1
T-
O
O_
CO
sJe),eu_!ll!U_ 1-17
(M O_
Ii
01
m_ !
! I
i
I
J 0 O_
i
i I
t
i I
E
O_ ............................................. t.......... _ ......... +...................... ._ ...................... CO
_m
0
{J .c: !
Im ....... "I" ....................................
i"_
O0 ¢0
..................................................
,
_
t
m G) >,
0
H._
J= _a
tIN
GO
I
0
L. I
(D GO
!
5
'
I
In GO
[
0 0
0 0
0 0
0 0
0 0
sJa),eUJ!ll!m 1-18
0 0
O0
N94-15554 L
Laser Ranging Network Performance and Routine Orbit Determination at D-PAF
F.-H.
Massmann,
Ch. Reigber,
J.C. Raimondo, Deutsches
Geod_itisches
German
C.
H. Li, R. Ktinig,
Rajasenan,
M. Vei
Forschungsinstitut
Processing
(DGFI),
and Archiving Facility MiJnchner Str. 20
D-8031
Abt.
I, and
(D-PAF)
Oberpfaffenhofen Germany
Summary ERS-1 the
is now about
very
8 months
beginning
of the
(D-PAF) is coordinating determination tasks. This
paper
presents
mission.
and
details
in orbit
and has been
The
German
supporting
about
the
tracked
processing
the network
global
by the global and
archiving
and performing
network
status,
laser
network
facility
the different
the tracking data and orbit processing system at D-PAF. The precise orbits are shown and some problem areas are identified.
quality
for ERS-1 routine
the communication
to D-PAF
of the
from
preliminary
orbit
and and
1. Background On July
17, 1991,
ly launched microwave to make
the first
from
Kourou,
instruments full
use
measurements
the satellite
ERS-1
laser
in a sun-synchronous
the satellite
The
Sensing
satellite
ERS-1
orbit
Satellite
is equipped
of the Earth's
the
ranging
and an inclination of 98.5 degrees Kepler period is about 100.5 min. To keep
Remote
environment has
(ERS-1) with (see
to be known
was
successful-
a number figure very
of active 1). In order
precisely.
is carrying a laser retro-reflector and, as an experiment, the Prare Range Rate Equipment). After the failure of the Prare system due
diation damage bit determination.
is flying
(ESA)
Guayana.
for the monitoring
of the
this purpose ERS-1 (Precise Range and
European French
ground
maintenance manoeuvres weeks depending mainly
tracks
(SLR)
circular with
within
measurements
orbit
different
(quasi-polar) ground
+-1 km deadband
have to be executed, on the solar activity.
1-19
are the basis
which
take
repeat
at a mean cycles
(first 6 months place
usually
For system to a ra-
for the precise
altitude (see
of 785 km
table
+- 2 km) every
or-
two
1). The
so called to four
Figure
1: ERS- 1 Satellite
Wind
1DHT Antenna
Table
1: ERS- 1 Orbit
Characteristics Repeat
Revolutions per cycle Revs per day Mean Semi-Major Axis [km] Mean Inclination [Degrees] Mean Eccentricity Mean Argument of Perigee Mean local solar time of descending node Longitudinal phase (ascending node) [degrees] (1) Venice (2) ICE Orbit Duration
3 days 43 revs 14 + 1/3 7153.138 98.516 1.165 xl0 -3
Cycle
35 days 1.501 revs 14 + 11/35 7159.4'965 98.5429 1.165 xl0 -3
I 176 days 2521 revs 14 + 57/176 7156.30 98.5114 1.165 xl0 -3
90.0 deg
90.0 deg
90.0 deg
10h 30min
10h 30rain
10h 30min
24.36 East O) 128.2 West _)
20.9605
not decided
26/07/91-12/12/91 23/12/91-30/03/92 16/12/93-01/04/94
1-20
¢1_' (2) (2)
East
2/4/92-15/12/93
8/4/94-...
2. ERS-1
Laser
The ERS-1 by many periods.
Tracking
satellite different
Network
is tracked institutes.
by a network In table
of globally
2 the stations
distributed
are listed
stations
along
which
were
with their ERS-1
funded tracking
In figures 2 to 4 the geographical distribution of the stations is plotted for the first three orbit phases (see table 1). As can be seen, most of the tracking stations are located in Europe and North
America.
The
southern
hemisphere
of them is located orbital passes.
in the south
Figure
Tracking
2: SLR
is covered
African
region.
Coverage
within
The
only by up to four plots
show
the Commissioning
also
the
Phase
SLR
stations
actual
(Venice
and
tracked
none ERS-1
Orbit)
9O
6O
5O
- 120
-60
50
1-21
120
180
Table 2:ERS-1
ID q181 1863 1864 1873
Tracking
Network
Location
Name
Stations
System
Potsdam Maidanak Maidanak Simeiz
Germany, Europe Russia, Russia, Russia, Europe
fix fix fix fix
1884
Riga
Latvia, Europe
fix
1893 1953
Katzively Santiago de Cuba
Russia, Europe Cuba, Carribean
fix fix
7046 7080
Bear Lake Fort Davis
USA, North USA, North
7090 7097 7105 7109 7110
Yarragadee Easter Island Greenbelt Quincy Monument Peak
Australia Chile, Pacific USA, North America USA, North America USA, North America
7210 7236
Haleakala Wuhan
Hawaii, USA China, Asia
7403 7512 7542 7810 7811
Arequipa Kattavia Monte Venda Zimmerwald Borowiec
Chile, South America Greece, Europe Italy, Europe Switzerland, Europe Poland, Europe
7824
San Femando
Spain, Europe
fix
7831
Helwan
Egypt,
fix
7835 7837 7838 7839 7840 7843
Orasse Shanghai Simosato Herstmonceux Orroral
France, Europe China, Asia Japan, Asia Austria, Europe Great Britain, Europe Australia
7882 7883
Cabo San Lucas Ensenada
Mexico Mexico
TLRS-4 TLRS-4
7907 7918
Arequipa Greenbelt
Chile, South America USA, North America
fix TLRS-3
7939 8834
Matera Wettzen
Italy, Europe Germany, Europe
MOBLAS MTLRS TLRS
mobile laser system modular transportable laser system transportable laser system
Graz
America America
North Africa
1-22
TLRS-4 fix
MOBLAS-5 TLRS-2 MOBLAS-7 MOBLAS-8 MOBLAS-4 fix fix TLRS-3 MTLRS-1 MTLRS-2 fix fix
fix fix fix fix fix fix
fix fix
Tracking
Periods
910720 910724 920421 910723 920501 910731 920225 920401 920422 910808 911127 910906 910822 911121 920318 910731 911018 910802 911211 910725 920504 910731 910929 920404 910731 920328 910729 910719 910807 911002 920107 911029 920505
.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
910803 920226 910717 910816 910720 910722 910719 910725 911117 920119 920414 920319 911113 920109 911129 920107 920404 910724 910918 920305
.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
910829 911028 920226 920515 910922 911015 910822 920124
920311
920306
920222 911010 920426 910917 910818 911006 920121 920327 911131
910729 911117 920127
911126 920208 911129 920115
910918
Figure
3: SLR
Tracking
Coverage
within
the First
Ice Phase
(Ice
Orbit)
90
6O
3O
..
,_ k./---_
.--.
--_0
V_
_.,
"
.W'/"(L
_........ -7_--,_-..
_._l_.
'V
)
,
,
. _i
_ _
•
I
_
_-._.
_"
I
/
.-_.,._:
_-/
....
_ '_ _"_.;'_k-'-_
-_,
I
-60
,
-90 -180
I
-120
Figure
4: SLR
-60
Tracking
0
Coverage
within
the first Month
60
120
of the Multidisciplinary
180
Phase
i
-180
-120
-60
0
1-23
60
120
180
!
3. Data Soon
Flow
after
to D-PAF
the tracking
a first data
Systems of a satellite
screening
then from each the measurements
pass the SLR
is performed
data is preprocessed
by most of the stations;
pass about 50 data were compressed
points were selected (quick-look (Q/L) into onsite normal points (ONP).
This Q/L or ONP data is then transmitted to the Data two centers collecting and forwarding the data: the data ted via
existing
second center the European these them The telex,
internal
links
to the CDSLR
transmission
Span,
Bitnet,
is performed Intemet,
from
CDDIS
and
by
It has to be noted,
that
able for all partners. performed the EDC According ties
(PAF)
and
merges
all three
parties
In the activities
to the work D-PAF
using
all
distribution
them
currently
the full tracking data or Span. Again D-PAF
exchange
the
their
mission
the four
the telecommunication
system
management
the trackfng subsystems:
and
system orbit
data
to have EDC
European
generation
orbit earth
determination methods, quality prediction different gravity solution
to CDDIS;
and
merges
communication
links:
set (full-rate (FR)) is retrieves the FR data files.
the full was
processing
of operational tasks
information
avail-
not established
D-PAF
D-PAF
and archiving
precision
orbital
has
faciliproducts
set up a number
system
(TOS),
of incoming
which
data,
consists
generation
of the
subsystem: differential orbit correction by numerical control, generation of numerical and graphical products orbit
extrapolation,
generation
of orbit
equation
systems,
1-24
quality
control
following
of normal
points
integration
prediction
formats, generation of time bias functions, quality control modelling subsystem: processing of surface gravity data, of normal
all data from China. From
(TCS)
determination
subsystem:
the
(DMS)
preprocessing subsystem: preprocessing from laser and altimeter data orbit
received
when
and for a processing of SAR data. In order to fulfill these of processing systems. Used for the orbit generation are:
the data
forwarded
available
with the directly
of the
between for
or
III and ftp.
beginning too.
is responsible
then
the collected data files on a daily basis have sent their data directly to D-PAF.
GE/MARK
EDC
and
(EDC) at DGFI. EDC is collecting from stations in Russia, Cuba and
After having applied all necessary corrections transmitted to the two centers, usually by CCT sets
data)
Analysis Center at D-PAF. There are from the CDSLR stations is transmit-
headquarters
is at the European Data Center systems (EUROLAS) and also
two data centers D-PAF is retrieving with data from those stations which data
at the station:
reduction
sets
in and
4. Station
Performance
At D-PAF
all incoming
data
is checked
for quality
and statistics
are generated.
On
a weekly basis Q/L reports are generated presenting incoming data statistics and data quality check information. This paragraphs will present some of the statistical information. As already served by
seen in figures 2 to 4 only a small part of the ERS-1 orbital path is obthe ground stations and this is mainly located north of the equator.
Especially over South America second phase and in the first tracking From the
in that part the figures
stations,
while
7 presents
only
week.
mainly
Figure
in figure
about
were
only
in the number
shows clearly was not in
is visible
For an arc of 7 days
the ascending
arcs
can be tracked
the variation
trend
that
a few descending
passes
It ranges from 0 to 13 and March 92, when ERS-1 corresponding
from the first phase there
to the is no
of the world.
it is also visible
is that the descending Figure
the situation became worse month of the multidisciplinary
tracked.
during
of stations
The
observed
reason
probably
daylight. observing
ERS-1
per day.
9 which
SLR
depicts
the
number
of passes
are available.
Stations
per Day
14
,tLil 0 0
100
150
o 3OO
200
elapse time [days]
1-25
by
a decrease for the months October 91 to sunlight for many of the stations. A
30 to 60 passes
7:ERS-1
arcs were
o=,,
per
There is also a wide range in the number of passes being tracked by different stations. As can be seen from figure 8 this varies from 1 to 217. But one has to keep in mind that not all stations were continously tracking, some were occupied only for a short while (e.g. Monte Venda, see table 2). The tracking contribution of some stations to the total ERS-1 tracking ranges from a few percent to almost 15 percent (Grasse). Figure 8: Acquired
ERS-1 SLR Passes per Station
st.R 0/t. o.d ONP Data (92/0S/13) Gralllle
Herstrnon. Potsdam
I I II IIIII I I II Iiiii I []II mmmmm
I I mi IIII [][] II III
m
m
217
,, I
•
i:-::i!!/.(.Fi_ ::_i_:_ _i-.-_: !ii-.::! _i
Yarragadee
mmmIl
I I II
Gmz
,,
Maul J4elwan
Mon. Peak
ii:,.'-:" _ :..;.:_'!_ _!_::'_ g9
:);i-.:_i ?1_4
Greenbelt Maldanak
71
Riga S. de
Cuba
[]
Zlmmerwald
5
Shanghai Slmasato
[] I [] 33
Mh Venda
Matera Qulnoy
3
Wuhan
28
Bear Lake
$
Easter Iw.
;
L
Adrmqulpa
N
Slmelz Kattavla
_a.S.Luoas WeHzell S.Femando
Orrorol rnsenada Mc.
Donald
Borowte© Greenbelt
Maldanak Arwquipa
o
50
100
150
200
no. of passes
:I_uROt_S
_Na,o-net
_Ru,,;*.
_O,h.,-.
DGFI Not only the data quantity is varying different. There are some stations with cm and less. Figure mal point accuracy
from single
10 depicts the station for some stations.
station to station, but also the data quality is shot precision of about 20 cm and others with 1
performance
1-26
in terms
of single
shot and
15 sec. nor-
Figure
9: Acquired
ERS-1
SLR Passes
per We_k
8O
70
DGFI
O 10.
Figure [¢m]
10:ERS-1
Tracking
Precision
per Station
(cm)
26
dam type
/
stad(mnarn8
1-27
15 soe. _ormnl truant
5. Orbit
Determination
In order generated
to provide ERS-1 and distributed:
orbit
predictions
at D-PAF
and
precision
time
orbits
the following
ERS-1
orbital
products
are routinely
bias functions
preliminary orbits precise orbits The
latter
details
two
about
proctucts the
description (1990).
of
The
data
overall
are official
ERS-1
all
radar
orbit
ESA
products,
predictions
altimeter
can
and
tracking
flow for the orbit determination Figure Int.
Organis.
11: Orbit ESA
while be
data
in Kt_nig
products
processes
Determination
Stations
the first one
found
is an internal et.al.
(1992).
is presented
is explained Data
in Bosch
in figure
Flow
SLR Stations
Data
Reception
Dlstrtb.
of Orbit
Reformatting
Predictions
RAFD
Screening
Orbit
Prediction
Plausibility Merging, Normal
Generation
Check Screening Point Generation
Orbit Adjustment Quality Control Comp.
with
Archiving
Submission
1-28
MMCC
of Orbits
of Orbits
one.
Orbits
More
A detailled
11.
et.al.
The
processing
schemes
are outlined
in figure
Figure
12 for manoeuvre
12: Processing
(for manoeuvre F
S
S
D
M
I
D
I
I
I
orbit
I
I
arcs
PRC
I
I
I
I
I
5-7
day orbits
_--
5-7
day overlap
arcs
Orbit
I
I
I
I
I
I
I
I
I
I
I
I
data
and
on a weekly are
points
be seen
periods
the
usually
basis
by using
available
from
figure
weekly
arcs
Q/L
within
(15 sec. bins for SLR,
six orbital
coefficients, stations
I
I
I
I
I
I
I
I
two
plus
radar
altimeter
Both
for RA-FD)
data
another
and
weeks.
10 sec. bins
14, the use of RA-FD
are computed
laser
elements
altimeter
range
at epoch,
improves
7-day
data after
fast
sets
are
first qual-
the global
arc which
bias
one
solar
radiation
cover-
is overlap-
orbital
(if RA-FD
data
is used)
and
of bad
data
cm. The
Figure 13 presents the quality control results from overlapping large values in November 91 are resulting from a period with few
coefficient, station
daily/halfcoordinates
only).
resulting
a very
I
®
The
only
I
days and is used for quality assessment (see figure 12). The models for the orbit are described in Zhu and Reigber (1991) and Massmann et.al. (1992). Solve-for are
drag
I
@
free
(for new
I
@
I
(3
In manoeuvre
daily
I
@
for arc with only a few SLR passes.
parameters
I
@
age especially
ping by 3-4 determination
I
@
I
are computed
As can
->
Determination
into normal
ity checks.
I
@
_i
(RA-FD)
I
@
@
compressed
I
I
7 day overlap
delivery
D
I
_ _'///ii/II/ilIA.---
@
orbits
M
I
10 days
_-_I
7 day orbits
Preliminary
S
I
2
PRL
5.1 Preliminary
S
I
I0 days
,
3--4 days
Scheme
F
I
, orbit
periods.
free periods)
M
I
free
laser
fits are usually
passes.
The
around
same
50-80
cm, in case
hold for the end of December
1-29
coverage
up to 130
arcs for 1991 and 1992. no useful RA-FD data and 91.
Figure
13: PRL
Precision
Assessment
by Overlapping
PRL
Radial
RMS
Arc Comparison
Differences
Ioo
I PRL
Cross-track
RMS
Differences
PRL
40(
_x
2ix
loc
1-30
Cress-treck
RILLS
Differences
Figure
14: Input
Example
for the Preliminary
(January
20-27,
• .go
Orbit
Determination
1992)
!
6O
3O
\
i
i
I -go -1BO
-120
5.2 Precise The
Orbit
precise
15 sec.
availability in between
0
12o
60
18(
Determination
orbits
normal
-60
are based
points.
The
up to now orbits
only
on laser
are computed
with
data
which
a delay
of all FR laser data at D-PAF. The arc length two manoeuvres and is usually in the range
have
of 3-6
been
months
compressed depending
into on the
is choosen to fit as good as possible of 5-7 days. The quality control is
also performed by overlapping arc comparison. Models and solve-for parameters are the same as for the preliminary orbits, except the earth rotation parameters, the geomagnetic indices and the solar flux data, which are now the official final values instead of predicted or preliminary ones. Figure 15 presents now while figure comparing erally one due
figure 13 and 16 one has to be careful, can say that the PRC results are more
to better
ponent
the resulting rms orbital fit values for the precise orbit arcs generated 16 shows the quality estimates from the overlapping arc comparison.
input
of the orbit
data seems
and
a more
intensive
to be accurate
data
because the arcs are not the same. But genhomogeneous and do not show large spikes handling.
to 50 to 60 cm.
1-31
up to When
The
most
interesting
radial
com-
Figure
15: PRC Orbital
Fits
(_)
F
i
i +
I
200
210
!
i
.....
220
230
240 DlyI
Figure
16: PRC
Precision
250
260
270
In 1991
280
q,_w_,_m._
Assessment
by Overlapping
Arc
,_e_,
Comparison
PRC Radial RMS Differences m)
r
18(
16(
-----
14(
/
12: 10(
---
,
:
_
I
2OO
210
220
230
PRC Cross-Track RMS Differences
_
200 (°m)
1_.
i
|
I
IR--
240
II
_! 250
260
270
PRO Along-Track RMS Differences SOo_orn)
.
O_m In 111_
_
1-32
270
6. Conclusion Soon
after
the ERS-1
launch
DGFI/D-PAF
ed its capability to generate good SLR stations have demonstrated tracking
there
preliminary and the SLR data.
and demonstrat-
quality orbits on an operational basis. On the other hand the their capability to track ERS-1 and provide high quality
to now
are
a few
precise
orbits
there
are only
things
that
is very
a few
could
much
stations
identified
Russia.
The temporal passes) were capability
coverage suffers from tracked by the stations.
of the station,
to the
ing periods information
data
partly
coverage
the fact A reason
tracking
spatial
hemisphere
accuracy and
of the
temporal
of which
generated
coverage
only
one
of
has a
only one tracking station can be found and the northern hemisphere some gaps can be
that mostly the for that is partly
restrictions
it is difficult
with high solar activity. derived from Spot2 Doris
The
by the
in the southern
record. On the African continent in North Africa (Helwan). On
over
be improved:
limited
good tracking that is located
Due
the orbit computations
data.
Nevertheless
Up
has started
to model
and partly large
ERS-1
ascending ERS-1 arcs (night the missing daylight tracking
man drag
power
problems.
perturbation,
Tests are initiated to improve this data or by using crossover altimeter
especially
by using data.
dur-
either
drag
References Bosch,
W.,
Flechtner,
F.,K_Snig,
Wilmes, H., 1990. ment. D-PAF/DGFI, K_Snig, R., Li, H., racy
Massmann,
of ERS-1
Orbit
Massmann, F.-H., Reigber, 1 Orbit Determination Symposium Zhu,
R.,
Massmann,
The German Document F.-H.,
F.-H.,
PAF for ERS-I: ERS-D-PSD-30000, Raimondo,
Predictions,
Positioning,
S.Y. and Reigber, Ch., D-PAF. D-PAF/DGFI,
1991. The Document
and
Reigber,
Ch.,
Schwintzer,
P.
Product Specification 1.1, Miinchen. Ch.,
1992.
On
and
Docu-
the
Accu-
this proceedings
Ch., Raimondo, at D-PAF,
on Satellite
J.C.
Reigber, RAT Issue
J.C. and Rajasenan, C., 1992. Operational ERSProceedings of the Sixth International Geodetic Columbus,
Ohio
r.-
German PAF for ERS-I: ERS-I ERS-D-STD-31101, Miinchen.
1-33
Standards
used
at
N94-15555 Laser
ranging
application
to time transfer
and to other Japanese Hiroo
KUNIMORI*,
" Commumcations
Research
Laboratory,
Safety
Academy,
satellite
space programs
Fujinobu TAKAHASHI*, and Atsushi YAMAMOTO**
Tokyo ""Maritime
using geodetic
Toshikazu
4-2-1 Nukui-kita,
ITABE*
Koganei-shi,
184 Japan
Wakaba-Cho
5-1 Kure-shi,
Hiroshima
737 Japan
ABSTRACT Communications Research Laboratory (CRL) has been developing a laser time transfer system using a satellite laser ranging (SLR) system. We propose Japanese geodetic satellite 'AJISAI', launched in 1986 as a target satellite. The surface is covered not only with comer cube reflectors but also with mirrors. The mirrors are originally designed for observation of flushing solar light _'eflected by the separate mirrors while the satellite is 'spinning. In the experiment, synchronized laser pulses are transferred via specified mirror from one station to another during the satellite is up on the horizon to both stations. The system is based on the epoch timing ranging system with 40 ps ranging precision, connected together with UTC(CRL). Simulation study indicates that two stations at thousands of km distance from each other can be linked
with
signal
from AJISAI AJISAI pass.
strength
mirrors
give
of more many
than
chances
10 photons
and
to two stations
the distributed to link each
images other
of laser during
In other topics on the application to Japanese space programs, Retro-reflector for Advanced Earth Observation Satellite (ADEOS) and RendDezVous docking Experimental Technology Satellite-VII (ETS-VII) are briefly presented.
1. Laser
Time
Transfer
via Geodetic
Satellite
beam
a single
In Space mission of
AJISAI
1.1 Introduction Users of time comparison techniques
and frequency standards have been able to take a variety of time even if they pursue the highest accuracy. The precision of GPS common
view observation, for example, have precision have been attained by radio (Ref.1). The requirement space geodesy, relativity
got to several few nano seconds techniques such as two way time
and 1 ns or higher transfer via satellite
of such an extremely high precision may exist in deep space navigation, physics and astronomy which always demand extreme precision and
accuracy in their measurements. In addition to the radio techniques, time transfer using optical pulses has recently been suggested as one of potential for giving precision of sub-nano or picosecond time transfer to overcome the maximum bandwidth of radio waves (Ref.2). Satellite laser ranging (SLR) have progressed as one of space geodetic techniques in the field of global geodesy and geophysics. Some SLR stations measure the range to as precise as 30 ps or higher (Refs. 3,4). Since the SLR system is essentially a highly precise epoch recorder transmitting and receiving of optical pulses, a combination of two or more SLR systems has potential as a highly precise time comparison and transfer system.
1-34
Illlqdlll_
m
¢_cit
(a) Fig.1
There
are
(b)
Configuration of Laser time transfer (a) One way uplink (LASSO) (b) Two
two
configurations
considered
way
for ground-based-laser
time
transfer
system
using a satellite (See Fig.l). The first is called the one-way up-link configuration. Both SLR stations transmit a laser pulse to the time interval unit (TIU) on the satellite and the TIU measures the interval between their arrival times. Such an optical time comparison has been performed in Europe in the LASSO experiment (Refs. 5,6). In the European phase, laser echoes were successfully received at Grasse, European laser ranging sites. The second is the two-way configuration. laser pulse to the other station via a satellite with mirror reflectors. The cube reflectors for conventional SLR, and they are used to determine station to the satellite'to give support to the time transfer solution. In the
two-way
configuration
concept, calibration system performance for two-way 1.2 Target
using
methods, is based
the Japanese
SLR
satellite
LASSO experiment of France and at other Each station transmits a satellite also has comer the distance from each this paper, we examines
AJISAI,
including
time
signal strength and spatial distribution of the reflected on the CRL SLR system (Refs. 7,8), including additions
time transfer. satellite
AJISAI Table
Launch
1 • Major
Date:
specifications
August,
1986
Configuration:
Polyhedron
Weight: Comer cubes:
685kg 1436 pieces,
Number
of mirrors
inscribed
:318 pieces,
40 rpm Altitude Inclination
in sphere
Effective
Reflective efficiency: 0.85, Duration of a flash :. 5 msec, Spin rate: Launch orbit:
of AJISAI
of diameter
2.15
area :91.2 cm 2
Curvature
of mirrors
Brightness
:
Rate of flashing
:8.4-9
1.5-3.5
1-35
Eccentricity
m
star mag.
: 2 Hz
1500 km, 50 deg,
m
0.001
transfer
beam. The to be made
z
•
•
Vlau_ sp_'.
,
Fig.2
w_h mirror1
Arrangement of mirrors on AJISAI Parts of an 8.5m radius virtual sphere (mirror) is placed on the surface of the i-m radius AJISAI maintaining their latitude angles.
AJISAI is the Japanese geodetic satellite launched in 1986 by the National Space Development Agency (NASDA). The major specifications of AJISAI are listed in Table 1. The satellite is a hollow sphere 2:15 m in diameter and weighs 685 kg. The surface is covered with mirrors
as well as corner
cube reflectors.
The orbit is a circular
with an inclination
of 50 degrees
and an altitude of 1500 km (Ref.9). The mirrors were originally designed for observing flashing solar light reflected by separate mirrors while the satellite is spinning at about 40 rpm. Each mirror is a piece of a surface with a radius of curvature of 8.5 m. Three elements from the same latitude of the 8.5-m sphere at longitudes of 0, 120 and 240 degrees areput on thesurface Of a 1-m radius satellite retaining the phase angle of the original sphere (See Fig.2). The latitudes from which every set of three is taken are uniformly selected from the original surface so that a distant observer rotation. 1.3 Two way
can observe
developed
1 is ahead
from
the front
surface
flashing
three
times
per
time transfer
The equation being
the light reflected
for two-way
in radio
of clock
frequency
2) between
dt2= (tertle+tl-t2)/2
time transfer band
the clocks
+ (RIe-R21)/2c
where
• (t;j =1, 2),
t,.
Epoch of pulse departure
via laser
pulse
is in principle
(Ref. 1). The time difference of stations
1 and
2 is given
the same
d_2 (: positive
as those
when
clock
by:
(1),
at station i measured by station clock i,
(i .NE.j_ Epoch of station i's pulse reflected station j measured by station clock j,
1-36
by a satellite
mirror
arriving
at
=
=
Re :
(i .NEd') One-way distance via the satellite, and
c:
speed
pulse to travel from station
to stationj
i
of light.
The last term (Rlz-Rzt)/2c travelling is related
of a laser
is expected
paths, but not negligible to the difference between
to be nearly zero because
of the good
symmetry
of
due to the effect on motions of both satellite and stations. It the satellite position at the times the two laser pulses arrive.
It approaches zero if the two pulses arrive at nearly the same time on the satellite. This is done by controlling the firing timing at both stations. Timing control within the precision of 1-ms is necessary to obtain a station to station link by a mirror of AJISAI with 20cm x 20cm size spinning at 40 rpm. If the laser fire timing is controllable to l_s, (RIz-Rz)/2c is down to a few ps on the assumption that both the predicted position of the satellite and the clock synchronization are known with the accuracy of less than 1 _ (300 m in distance) before the experiment. The Its firing control can be performed by a fully active mode-locked laser operation. In this observation mode, we can apply the geometric method rather than dynamical one to the orbit solution using SLR range data (Ref. 10). 1.4 Laser ranging system We use an active-passive
mode-locked
optical
pulses
100
ps
wide.
The
energy
is 100
mJ
per
pulse
and
repetition
rate
mode-locking firing
can
passive the
be controlled
by a saturable
Nd:YAG mode-locking
nominal
from
laser to generate is performed
repetition
7 to 14 pps
dye is replaced
by
by
with an active
real-time
nm wavelength
saturable
rate is 10 pulses
per
software.
component,
detector
can be also gated
temporarily
by the prediction
arrival
receiver,
The timing system consists of a high performance disciplined and a time interval unit (TIU). Either a GPS timing receiver
(CRL)
can keep
a resolution
the reference
to UTC.
Timing
epoch
is measured
is transmitted
to the SLR
we must
system
consider
If the
plate
in 20-ns
via a 500-m
optical
5-MHz
used
and
of UTC.
to the clock
long-term
of photo
efficiency The MCP time steps.
quartz oscillator, or cesium clock
via cables
and electronics.
signal
a GPS of UTC with
Furthermore, clock
of the atomic the laser
and the TIU
fiber.
signal
as the reference The
5-MHz
room. Then
monitored stability
Output
(50 MHz) of the quartz
frequency
and 1-pps delay
at the clock
in TIU.
signals
and phase room.
of the system.
1-37
1 pps signal
are combined
difference
It has
The
been
oscillator again
with respect installed
clock
transmitting
is monitored
an independent measurement system. Figure 3 is a block diagram of the monitoring in the experiment. The combined 5-MHz+l-pps signal from the cesium clock room
continuously
passive
for up to 4 stop events
that the reference
and receiving point is not at the telescope reference point. The cables and electronics delay between the atomic
back
The
of 40-ps.
Calibration system In the actual experiment,
reference
The
the synchronization
rise time, 8% quantum fraction discriminator.
of photons
dye.
second.
timing can be controlled on nanosecond level (Ref.11). The receiving telescope aperture has diameter of 1.5 m. A micro-channel
multiplier (MCP-PMT) is used for detector. It has a 300-ps and the transit time jitter of less than 30 ps with a constant
1.5.
532
by
system used is transmitted
is phase-locked
by the
is used
epoch
at SLR
for the
site
to the original
and are sent signals
to get the characteristics
are
of the
s
Optics[ Fiber (50O I)
5_z
$r.ar t T I Stop
IP_ > i
5 _z
C
_ I PPS
[-'-I TIC: T[ae cs:
Interval
Cesim
Co,rater
[
'
Standard
great tiniag Telescope _._z t.ro [ [J_ER flrs ti_ial
Fig.3
The epoch occurred target
latch point
at the telescope
its physical
distance
=(te;-tle+t;-t + {
signal
at each laser pulse point
moving
from reference
The time difference
d;2
Reference
reference
is put on the telescope
( intersection
clocks
including
in addition
Optical
path delay
tL_
Electronic
delay from firing
ti.y "
Electronic
delay from receiver
and
electronic
delay,
measurement temperature.
must
it will the
wotald
from
firing
axes).
The
events
calibration
of transmitting
beam
and
precisely. term
(d';2) is given
by:
in time
common
portable errors
defined input)
reference
point
in Eq. 1, point
point
unless
design
can
from
to receiver
be the
reference point
latch gate
is changed.
value
of parameter
two
dependence
on
signal
or
out
the
stations. strength
This and
1.6 Link budget ground
In the laser time transfer experiment, the number of photons station are calculated according to the following equation: Np=(E)Jhc)(Grer where
f ,2)'(16Ae4 JnZR,2ReZq,2q,2)
E" Energy h • Planck's !"1 •
in a pulse, constant,
Transmission
(Np) detected
at the remote
(3)
_ • Laser wavelength, c • Velocity of light, beam efficiency, 1-38
re • Receiving
beam
efficiency,
E
meter
To cancel
at
i,
i.
by a distance
collocated
at
i, and
at station
1 and 2, each
point
at station
at station
can be measured
optical
receiver coming
clock
delay
to telescope
latch gate
to stop-epoch
between
The optical
be stable
(2),
}/2
point to start-epoch
the time difference
have
r)
(laser
from telescope
be evaluated.
still
reflection
calibration
to the parameter
ti. b "
to calibrate
of two rotation
as if these
2 )/2 + (R,e-R21)/2C
path delay i,
by scales,
start and stop must be treated
point must be measured
between
system
axis, as it takes partial
Optical station
In order
monitoring
(tla-tlj,)-(t2_-tza,)+(tz._+t2.r)-(tL_+tx.
: (i=1,2),
in { } in the Eq.2
MONITOR
Target reflector reflectivity, Atmospheric transmission efficiency (one-way), Total reflector surface area, A r : Received aperture surface area, Station 1 to satellite distance, R2 : Station 2 to satellite distance, Transmission beam divergence, and Reflectors beam divergence for incident fight return
1"3:
r,: A, : R1 : qt : q, : Figure
4 shows
the expected
number
of photons
for AJISAI
mirror
reflection
and
the
satellite elevation from stations, assuming the parameters have the values listed in Table 2. We also assume the position of AJISAI is roughly in the middle of the two station's common sky. From stations 2500 km apart, AJISAI is observed at above 40 degrees and more than 10 photons are expected.
Table 2 • Parameters for estimating Satellite Energy
Altitude
: 1500km
of pulse
Wavelength Transmission
the number of ohotons
(E)
(AJISAI)
: 100 mJ
(1) efficiency
: 532 nm (r_) : 0.6
Target reflectivity (r 3) Atmospheric transmission
: 0.9 efficiency
Receiving (r 4)
efficiency
,: 0.6
Reflector
surface
area (A,)
: 0.04 m 2
Received
surface
area (A)
: 0.27 m 2 (60cm
Transmission
beam divergence
aperture)
(q,) : 5 arcsec
5O
10o N
_
=
Z
ELEVATION(DEG)
B0
,o
60
30
fON
=
G v
(r2): 0.3
o im
O ZO
10
ZO
•
0
w
DISTANCE
Fig .4
-
2000
!
i
/
4000 BI!I'WEI'.'H
gO00 S'I'ATIOHS
ttl
o 8OO0 (kin)
Elevation and Expected number of photon v.s. distance between stations in laser time transfer via AJISAI
1.7 Spatial distribution of laser reflection
1-39
We simulate the spatial distribution of laser reflection from possibility of an optical link for time synchronization between stations. rotation project
AJISAI to study the We calculate first the
phase and the incident angle of AJ'ISAI for a given transmitting station and epoch, then the image onto the ground from all mirrors visible to both stations. The calculation
continues
according
to the given
time step.
In Fig.5, each rectangle is the image of the instantaneous laser shot and the number by the rectangle In Fig.6,
three
steps of 50 msec (one AJISAI
START TIME TIME INTERVAL INITIAL PHASE
spin)
are illustrated
successively.
8TART TIME TIME INTERVAL INITIAL PHASE
1987.8.27 12:22:0 0.0 (INSTANTANEOUS) 0.000 (DIEG) -
tgR7.11.27 12:22:0 0.IS0 (S) 0.000 (O8(31
IIo
m
ad
laser reflection on the ground for an shows the reflector number on AJISAI.
...'_1_ 114 ""-
--'""" Z
"''"
'''"
°'"°
In''" .
-_
"
w"¢_
. AJISAI
",_l.I.o
_
EO-
,_,. '_"_.-,,.,_ _._._.
___-_.L_,_..__
"_
,t,,.
,¢_j,.__-4xIl.,i...._l,,
,s,.
J
.. ¢,,...dt,
:t 4o
,dl' f'"
,
•
---......._,,.
_'ll,:_..,.4j_.
" .... :IIL_/_', _ -"_';_" _'_"
.;
"'41,,. ,.
"1"-
,_._
o_lt...,,0t:"
40
_ ,°i._'. Reference
#"
10
Slsllon
°
"N
90 neference
St|il()r_
_pv.
z0 I10
Fig.5
110 Longitude
1.10 Essl
140
IiO
II;0
(dog)
Instantaneous spatial distribution of reflected images on the ground via AJISAI mirror reflector. (The number next to each image indicates the mirror number on AJISAI)
A several stations'
to get
percent the link
of East every
Jzo
i_
Longitude
Asia
AJISAI
Fig.6
can locate pass.
an image,
If the timing
to Japanese
_4o
Space
but there
of every once
shot
is a chance
for many
is as accurate
every
few
seconds
as the by
Program
Table 3 lists the satellite name and its launching schedule in Japanese program. The schedule is released before the H-II rocket engine explosion which least one year delay shift from original schedule. 2.1
t_o
(deg}
Spatial distribution of reflected images in three 50 msec steps. (The number next to each image indicates the mirror number on AJISAI)
prediction, time comparison can be performed on average simultaneously determining the rotation phase of AJISAI. 2. Application
El'It
R&D space will cause at
RIS
Retro-reflector Observing Satellite)
In Space (RIS) is one of missions on ADEOS (Advanced Earth satellite which is scheduled for launch in 1996. The orbit is a sun
synchronous sub-recurrent polar-orbit with an inclination of 98.6 deg. It has a period of 101 minutes and an altitude of approximately 800 km (Ref.12). RIS is a single element cube-corner
1-40
Table
3 R&D
Satellite
Schedule released Fiscal
Launching
(1992-
by NASDA
year/Satellite
...........
2001), Curved surface
in April 1992 name /_.,.
n .......................
1992
JERS-1,FMPT
1993
ETS-VI,
1994
IML-2,SFU
1995 1996
ADEOS cOMETS
1997
TRMM,
1998
JEM-1,2,
1999
JEM-n
2001
HOPE
__..
_lat_urface
SFU
ADEOS-II X: Direction of satellite movement Z: Nadir
Fig.7 Structure of RIS ( Effective diameter" 50cm
retro-reflector
with
a diameter
of
0.5 m designed
for
earth-satellite-earth
)
laser
long-path
absorption experiments. RIS is proposed by the National Institute for Environmental Studies collaborated with CRL. In the experiment, laser beam transmitted from a ground station is reflected by RIS and received at the ground station. The absorption of the intervening atmosphere is measured in the round-trip optical path. surface for one of three
Figure mirrors
7 shows the structure of RIS. We use a slightly curved mirror forming the retro-reflector, which diverges the reflected beam to
overcome
the velocity aberration caused by the satellite movement. We have proposed a simple spectroscopic method which utilizes the Doppler shift of the reflected beam resulting from the satellite movement for measuring the high resolution transmission spectrum of the atmosphere. The wider laser beam is used for illuminating satellite and for autonomous tracking the satellite by guiding camera. 2.2 ETS-VII NASDA
will
schedule
to launch
the Experimental
Technology
Satellite
(ETS-VII)
in
1998 whose objectives are development of space robotics and rendezvous control. It consists of two satellites, the chaser and the target, each has GPS receiver for orbit control of chaser. Tentative altitude is 550kin and communication to the ground will utilize the data relay satellite. We have proposed that each satellite should be loaded with corner of which is two-color sensitive and be monitored the rendezvous process will track the satellites with switching or simultaneously mode depending within
one beam
cube reflector set, one from the ground. We on two satellites being
or not. 3. CONCLUSION
We synchronization whose
timing
have
studied system
system
with
the
feasibility
a target
is connected
satellite
of
the
of
AJISAI
with UTC(CRL).
1-41
sub-nanosecond based
on CRL
precision laser
laser
ranging
time
system,
Simulation can be linked beam from chances
study
by laser
AJISAI
indicates
beam
mirrors
that two stations
with signal is uniformly
to link each other during a single
The system to the major determined
has been
geodetic
operating
satellites
with the precision
system space
from
AJISAI
in geodetic 1990.
of km distance
than 10 photons.
on the ground pass.
information
of several
has also for time program in future.
at thousands of more
distributed
timing, however, it bring on the precise satellite range data.
current Japanese
strength
from
The
each other
images
and two stations
It requires
of laser
have
the lasec control
many
of laser fire
of the orbit as well by using the self-returned mode
since
While global centimeters,
synchronization
CRL started the SLR observations
position
of the SLR station
we are re-designing mode
operation
has
our system
as well
as
been
so that
adapting
for
REFERENCES ,
2. .
4. 5. 6. 7. 8. 9. 10. 11. 12.
Kirchner D.,1991, Two-way Vol.79, No.7, pp.983-990 Leschiutta S.,1991, No.7, pp. 1001-1008.
Time
Time
Transfer
synchronization
via communication using
laser
Degnan JJ., 1985, Satellite Laser Ranging : Current Trans. Geosci. Remote Sensing. GE-23, 4, pp.398-4
satellites,
techniques, Status 13.
_,
and Future
Pearlman M., & al. 1989 , Ground-based laser ranging measurement technology, _g.09.13...QLC,,J_-COOLFONT, section2.1, pp. 1-26. Serene B. and Albertinoli P. 1979, The LASSO Experiment, Proc.PTI'I pp.145-167.
Vol.79, Prospects,
and
1 lth conference, D l[ i
Proc.7th
Kunimori H. & al. 1991, "Satellite ,pp.303-317.
of CRL.
ranging system",
IEEE
techniques
Veillet C. 1989, LASSO - the European Phase Aug.88-Sept.89, Workshop on Laser Ranging Instrumentation, Matera 2-6. Laser
_..Qg,_.L_,
International Z
Journal
Greene B.A. 1984, Epoch timing for laser ranging, Proc. 5th International Laser Ranging Inswumentation (Herstmoncex), pp.247-250.
Vol.38,
No.2
Workshop
on
Sasaki M.and Hashimoto H. 1987, Launch and observation program of the experimental geodetic satellite of Japan, IEEE Trans.Geo.Rem., GE-25, 5, pp.526-533. Yang F.M. 1986, The proposal of strictly simultaneous satellite laser ranging, The 6-th international workshop on laser ranging instrumentation, France, pp.549-557. Electro Optic Systems 1991, EOS-V1 Active/Active Laser Characterization. Sugirnoto,A., Minato A. and Sasano satellite, CREO'91 Baltimore,.
Y.,19_1,
1-42
Retro-reflector
in space
for the
ADEOS
N94-15556 APPLICATIONS
OF SLR
B.E. Schutz Center
For Space
Research
The University of Texas at Austin Austin, TX 78712, USA
INTRODUCTION Satellite
Laser
Ranging
10 meter-level
(SLR)
first generation
to the
began,
in part, as an interesting
science
systems
that
systems.
ments
component
has a rich
of modem,
now
history
These
produce space
systems
several
application
precision
of development evolved
which
began
with order
millimeter
single
of the new laser
geodesy,
which
in the
of magnitude
shot
range
technology
contributions
with
improve-
precisions.
has become
in turn enables
1960s
What
an essential to a variety
of
areas.
Modem
space
cision
geodesy
geodetic
Ranging butions
is the beneficiary
measurements.
Aside
of technological fro SLR
and
(LLR), Very Long Baseline Interferometry also. In recent years, the Global Positioning
developments
its closely
which
related
have
technique,
enabled Lunar
preLaser
(VLBI) has made prominent science contriSystem (GPS) has demonstrated a rapidly
growing popularity as the result of demonstrated low cost with high precision instrumentation. Other modem techniques such as DORIS have demonstrated the ability to make significant science contributions; furthermore, PRARE can be expected to contribute in its own right. An appropriate question is "why should are several answers, I offer the opinion
several techniques be financially supported"? that, in consideration of the broad science
the benefactors of space geodesy, no single tations of the science areas in which space ing. The more well-known rotation/orientation, gravity name
While there areas that are
technique can meet all the requirements geodesy contributes or has the potential
science areas include plate tectonics, (static and temporal), ocean circulation,
and/or expecfor contribut-
earthquake processes, Earth land and ice topography, to
a few applications.
It is unfortunate
that the modem
this view is usually diminishing reduce
the data
physical
encouraged
budgets.
The
space
by funding
techniques
to geodetic
techniques
competition,
are, for the
parameters
from
especially
most
several
are often part,
techniques
viewed
as competitive,
in an era of growing
complementary promotes
and
but
needs
the
but
ability
to
confidence
in the geo-
in the context
of the other
interpretations.
In the following
sections,
the current
techniques.
strengths
and
prospects
geodesy
The
SLR
limitations
applications of SLR
are reviewed
are reviewed
and
speculation
about
the
future
are offered.
SLR Summary Satellite transmitter
Laser
Ranging
to a target
measures and back.
the round-trip Current
time-of-flight
and near-term
1-43
satellite
for a laser targets
pulse
include
to travel
Starlette
from
(1000
a
km
altitude),
Ajisai
km).
Future
1992
launch).
lifetime offering
(1500
km),
satellites
include
The
measured a distinct
ERS-1
geodetic
(800
kin),
Lageos
TOPEX/POSEIDON satellites
(59000
(August
(Starlette,
Ajisai,
km)
1992
by the
extragalactic Precision
and
The
and
-2 (25000
and Lageos-2
(October
Etalon)
have
a long
orbital
in thousands of years to millions of years for the high altitude satellites, thereby advantage that the satellite will be available at no cost for a very long period of
on-board radio
Orbit
Etalon-1
launch)
Lageos
time. Only the ground segment requires operation and maintenance satellite techniques (GPS, DORIS, PRARE) rely on an active space mined
and
power
sources
system,
which
usually
several
will, presumably,
years.
support. segment
VLBI,
be available
By contrast, all other with a lifetime deter-
on the
other
hand,
uses
for a very long time.
Determination/Gravity
traditional
strength
of SLR
has been
in the ability
to determine
the orbits
of target
satellite
with high accuracy. In the case of TOPEX/POSEIDON, SLR is the primary means of precisely determining the orbit to the required 13 cm in the radial component in support of radar altimeter analyses. SLR tracking of NASA altimeter satellites has been an important element in the accomplishment dependency potentially SLR, tems.
of the respective on atmospheric able to provide
mission goals, SLR, however, has a distinct disadvantage transparency. Radiometric systems, such as GPS and essentially continuous tracking. Since TOPEX/POSEIDON
Created by DORIS, are includes
GPS and DORIS, it will provide a unique opportunity tO evaluate the performance of all sysThe focus of tracking systems on future satellites may be GPS with SLR as a backup. Nev-
ertheless,
it is important
to note
that
the passive
nature
of SLR
provides
an extremely
reliable
space segment--it simply will not fail except under catastrophic circumstances. A cautionary note for the future is in order. The risk of regarding SLR as a backup system encourages the reduction in operating systems for budgetary reasons, but as systems close, it becomes more difficult to reactivate them in the event that the backup mode must be initiated. Improvements
in the
gravity
field,
including
the gravitational
parameter
where SLR has made very significant contributions. The development tion for TOPEX/POSEIDON have benefitted from the SLR data base
GM,
are
other
areas
of new models in preparathat has been accumulated
over the years, some of which has been used in previous fields and some has not. Gravity fields used for GPS applications, such as the Department of Defense WGS-84, have used SLR data from Lageos gravity have
and Starlette coefficients. relied
which have particularly contributed to determination of low degree and order Current GPS applications use GEM-T3 or other, more recent fields, which
on SLR
data.
Furthermore,
the Etalon
satellites
effects that will be somewhat similar ular GPS effect of deep gravitational
to those influencing resonance.
SLR
to the study
has made
unique
contributions
tidal and non-tidal
variations.
These
studies
area-to-mass
satellites
(Lageos
and
the
opportunity
This
ratio
diminishment
effects. Furthermore, investigate the orbit years.
enhances
can be used
the GPS satellites,
of temporal
variations
have, in part, been Starlette),
which
to identify
the
gravitational
except
for the partic-
in the gravity
made possible
diminish
to study
by the nature
the nongravitationai
spectral
field,
content
both
of low forces.
of gravitational
the study of temporal changes in gravity has been enhanced by the ability evolution over long periods of time, spanning in some cases more than
to 15 i
| 1-44 E
Earth
Orientation/Reference
Frame
All satellite techniques are, conceptually, ter of mass. VLBI, by using extragalactic ever,
if VLBI
is used
to track
satellite techniques. The has been a consideration Rotation
Service
All space
artificial
satellites,
VLBI
would
have
with the cenof mass; how-
the sensitivity
of the
Reference
techniques
Frame.
have demonstrated
sensitivity
to polar
motion.
Current
comparisons
between polar motion series obtained from SLR and those obtained from VLBI show at the 0.5 milliarcsecond level. GPS developments are underway, including the proof International
other
SLR precision and long term continuity (Lageos was launched in 1976) in adopting the SLR origin to be the origin of the International Earth
Terrestrial
geodetic
able to define a reference frame coincident radio sources, is insensitive to the center
GPS Geodynamics
Service
(IGS)
slated
to begin
in June
agreement of concept
1992.
VLBI provides long term UT1 that cannot be matched by the satellite techniques at the present time. Lageos has been demonstrated to provide independent determinations of UT1 over a 50 day interval.
The
higher
altitude
of the Etalon
satellites
suggests
that a much
determination is possible, but the sparse SLR tracking of the Etalon limited demonstrations of the UT1 capability. It is worth emphasizing ratio of Lageos
and Etalon
The nongravitational satellites
to very
Comparisons ments, either
result
forces
in much
smaller
are a significant
short term UT1 (sub-daily
have been permanent
nongravitational
factor
longer
period
of UTI
satellites has allowed only that the low area to mass
forces
in the GPS satellites
than
the GPS satellites.
that limit the use of these
to a few days).
made between SLR and VLBI reference frames using collocated instruor mobile. These comparisons have shown agreement at the 2 cm level.
FUTURE With
the launch
years,
a second
of Lageos-2, Starlette
satellite
our knowledge
about
gravity
for science
models
lites,
for example,
only
high precision of the diverse
one satellite
process
variations
New
will be launched. in the gravity
improved
developments
quick-look constellation
can be ranged
of establishing
will be two Lageos
applications
will enable
tion of site positions. provide tracking
there
priorities
and two
Starlette
Etalon
and Lageos
satellites. have
field as well as contributing
and for precision Earth
rotation
in on-site
orbit
software
have
and enhanced
provided
much
Two Lageos more
rapid
the ability
data that can be used for science applications of satellites now avail,able for SLR tracking.
at a time and the involvement
a few
to the development
determination.
determination
Within
of the science
of of
satel-
determinaof SLR to
and to assure Nevertheless,
community
in the
is essential.
No single space geodetic technique can meet all of the application requirements of the science community. Each technique provides some unique contribution, though most of the techniques overlap in some areas. In an era of diminishing ance of techniques and the prospects of losing considered
as emphasis
budgets, the determination of the appropriate balor eliminating some science applications must be
is redistributed.
1-45
The
international
further
collaboration
collaboration
work, thereby understanding
in the
will enhance
assuring the continued of our planet.
SLR community
the prospects collection
1-46
has been
for long term
outstanding.
availability
of data for the purpose
The
promotion
of a global
of gaining
better
SLR
of net-
scientific
Timely
Issues
E
R_ B
zl m m_ E
N94Satellite
Signatures
in SLR
G.M. Royal
15557
Observations
Appleby
Greenwich Madingley
Cambridge
Observatory Road
CB3
0EZ,
UK
Abstract. We examine observations vation
the evidence for the detection of satellite-dependent obtained by the UK single-photon SLR system.
distributions
from
Ajisai
and Lageos
functions and from the characteristics tions. The effects of vamfing return mental
observations
photons
of Ajisai,
is achieved.
corrections
The
are developed
of the strengths
during
which
implications
s,ignatures in the laser range Models of the expected obser-
from
SLR system, are discused a range
of these
the published
for
spread
and compared with the observausing the models and by experi-
of return,
results
satellite
levels
from
single
system-dependent
to multiple-
centre
of mass
are discussed.
1. Introduction. The
UK SLR
system
sited
at Herstmonceux,
and
run
by the
Royal
routinely observes the primary tax'gets ERS-1, Lageos, Etalon-1 sai. The single-shot precision achieved by calibration ranging Tile detection and timing hardware has recently been upgraded Avalanche Epoch
Photodio(le
is derived
rangc return
(SPAD,
at present
Procha.zk_t
from
ctal,
a Maryland
1990), 4-stop
and event
Greenwich
Observatory,
and -2, Starlette and Ajiis close to 1 cm (1-sigma). to include a Single Photon
an HP 5370 timer,
time interred
which
is also
counter.
used
to make
measurements simultaneously and independently of the HP counter. Pass-averaged rates are in general fairly low, varying from a few percent from the Etalon satellites,
through
about
20%
fl'om
targets are deliberately ters in the laser path. return, carried becaxne
Lageos
kept Under
to up
to 50%
from
Ajisai.
Returns
from
to similarly low levels (about 10-15%) using such conditions we can describe the system
the
calibration
neutral density filas a single photorl
single photon detection system. A detailed study of the system error budget was out following the upgrade of the detector from a PMT. During this investigation it clear that the observational precision of in particular Lageos and Ajisai was consis-
tently worse than distribution of the
that of the retroreflector
calibration targets. It was considered arrays on the satellites would modify
likely that the the distribution
spacial of the
range residuals, when compared with those from the fiat calibration targets. In this paper we examine the evidence for detection of satellite signatures in our range observations, compare the observations with models of the expected distributions from a selection of those satellites
regularly
required 2. This
observed,
to reduce
the
and
discuss
observations
the
implications
to the
centres
in terms
of the
of mass
of the
range
residuals
appropriate
corrections
satellites
Observations. investigation
is based
upon
the
pass-by-pass
2-1
that
are
formed
during
the preprocessingstageto errors
in the
solves
for corrections
falling stage
predicted
outside
a 3-sigma
is fitted
shown
in Figure
cMibration values are
target plotted
distribution
Also
the
values
TaJICI[T
*
II)@Z
4
pass,
in the
Li
and
I, 11
1992,
these
residuals
iterative
•
distribution
the SLR Gaussian
system. The distributions,
600 m from of the fitted
•
kurtosis
would
be 0.0 and
:,%,..,,=. II
I_RS-
13@
?'.A) INI IIIg_
4 =
lai[lr=41.
,.
qla,
8
ZZ
1.1_6 IS
k'@rl_m,l.e7
I,_
-
- :--
' "
i
_|@1
g
rm
Ig
li|_
l@
ldt._l I_IGNAm
_lCVndl,f.4l
IKNi
]Ill 114
Zl
em
I_UIITI_43
Lageos
observed range which are also
l..II|
,_n- ,.,
1
to a
3.0 respectively.
-I@
IS
4 =
and
of ranges
li_-.tU.
i@e .58r.NA
bins.
_l?
j
lul
are used
in range
JIUIIIF=3.00
I@
•rao:igo
In a final
fitted distributions are shown, along and kurtosis. For a perfect Gaussian
•t
-I0
residuals
least-squares,
is a typical
11¢111|
.
to
iteratively
the residuals
the by
due
stage
proceedings).
performance,
by grouping
which
at each
@.34
x,,,._,
oil
this process,
rejecting
distribution
Figure
•-
=l
in the residuals
are used to make a final selection of the origin',.1 distributions and their fitted Gaussian distributions
i. I "*_1
•53.13'a
ra
Sinclair,
observed
about mean
of skewness
_lGllAi
ia
during
The standard deviations of the of the data, expressed as skewness
IINI
C lib
shown
board, distant relative to the
shown on each plot. with higher moments
and
for each to the
All trends
parameters,
che¢& on system
fitted Gaussian of the observed 1.
points.
are removed
(Appleby
as a useful
distribution
of the Examples
normal
of orbit-related
band and
distribution
the parameters observations.
on-site
of the satellite
a frequency
A normal
are
orbit
to a set
of pre-processing,
to form
compute
[email protected]
p*
Aj isa i
3..@ liT.
I;l;1¢ If ..e j..r.
r,l_
tu=r.=.jw Jill r
KInlT*3.S4
_Lolon-
l
_.
lIA m
d_lll
_,., p,
m
E_
k
-i@
g _10
•
I|
tm -I@
Figure
1. Observed
distributions
of range
2-2
residuals
from
calibration
•
and
satellite
IO
em
targets.
2.1
Discussion.
From
the
butions
distributions
of the
shown
calibration
in Figure
ranges
and
1, we make
those
the
following
fl-om Starlette
and
observations.
ERS-1
The
are clearly
distri-
symmetric
and well-fitted by the Gaussian distributions, but all have a significant 'tail' of observations outside the fitted curves. Skewness values for these 3 targets are between 0.05 and 0.1. The Lageos distribution is much less symmetric, and is less well fit by the Gaussian distribution. A chi-square goodness of fit test indicates significant departure, at a 5% level of significance, from the best-fit distribution shown in the plot. The results from Ajisai and Etalon 1 show large
asymmetry,
and
are
not
at all well
fit by the
Gaussian
distributions.
Of particular
significance to this investigation, are the 'widths' of the distributions, characterized by the standard deviations of the fitted distributions. Mean values of these standard deviations for a number of observations made during November and December 1991 arc given in the Table below. that
These the
largest,
mean
values
calibration the range
of standard
ranges
have
of standard
the
deviations smallest
deviations
confirm
scatter,
being
and
from
Target
the
impression
those
given
of Ajisai
and
in Figure Etalon-1
1, the
1.1 cm to 4.8 cm.
a llll-n
Calib
11
ERS-1
12
Starlette
16
LAGEOS
18
Ajisai Etalon
32 48
Before proceeding to investigate the hypothesis that satellite signatures arc present in our observations, we first consider the possible causes of the 'tail' in the distributions, particularly evident in the calibration and Starlette data. We remark here that the existence of this tail does
not
constitute
the
thrust
of our
argument
that
we are detecting
satellite
signatures
our observations, board. We must cause the SPAD
since the tail is also present in the calibration ranges from therefore rule out such a target-induced effect and consider or the laser. In an experiment primarily designed to quantify
time-walk
a large
using
under
neutral
density
filters
In this way the average shot, as deduced fl'om Figure
2, where
expected,
the
range
as the
are
in the
single-event
Prochazka
the
(1992,
displayed
standard
strengths,
average
detector
private
deviations
increasingly
of photons
form
of the
was carried
reaching
as before.
distributions
The with
the
out
detector.
photons
originating
plots
show,
increasing
expect the contribution number of photons
receives
as
signal
of the laser in the return nearer
to the
plots also demonstrate that the extent of the strength, suggesting an origin within the laser.
communication),
2-3
ranging
was varied from about 0.5 to 50 photons per rates. A selection of the results is given in
in histogram
pulse. The with signal
calibration
number
laser pulse-width we would to decrease with increasing
leading edge of the transmitted tail in the distributions decreases However
signal
number of photons the observed return
strength, since for a given to the observational jitter train,
to vary
results
a reduction
of return
in
a flat target as probable the system
points
out that
correct
optical
alignment
120
'
'
I
'
'
'
'
I
'
'
I
I
Illll
200
IOO
(a)
n = 0.5
(b)n = 6
= 12
a=
13mm
150 0
o
60 100
E z
40
50 20
I
I
[
I
|
I
L___-_.A_
20
_
__ __l____d--k__L__.L
30
d0
20
30
40
250
200
0
200 i
--
t[
it J
150
o
._
Z]
100 I00
_
-
]
--
5o
0 20 Range
Figure
30 Residual
2. Calibration
40
20
(cm)
distributions
Range
as a function
2-4
of average
numbers
30 Residual
40 (cm)
u of returning
photons.
of the
SPAD
Resolution 3.
detector
of this problem
Satellite
We now
take
strength
system
with
the
convolved
pulse,
from
system-signature
it models of Lageos
upon
within
the
chip.
that
effects
the
of Lageos.
of changing
and
not
In this
which
(Fitzmanrice
of a computer
diffraction
cross
satellite,
estimate
pattern
tests
in polar
of each
row of reflectors
section
of the
to caxry of the mainly
et al 1977.)
simulation
distribution
parameters give, for the particular cubes, in rows, contributing to the
distance
effective
of the
polarisation,
its shape
Ajisa_ we use the results
the
centre
calibration
satellite return signatures, by For Lageos, we take the model
far-field
is the optical
We use
from
the
of expected and Ajisai.
row-by-row
Also given
of gravity.
distances
signature
of non-uniformity
experimentation.
single-photon
based
signal.
centre
we ignore
effects
in Fitzmaurice et al (1977). The cross-section and number of corner
of returning of known
further
1, and develop from the spread functions
presented the lidar
spacecraft
rings,
standard,
para_neters
orientation, orientation,
possible
Models.
as our
of cross-section
to avoid
awaits
Signature
shown in Figure convolution with
the
is essential
out
shape affects
To model
carried
out
fl'om
cubes
in their
a convolution
of our
of the
returning
pulse
the
amplitude
the
return
signatures
and
Hashimoto
by Sasald
of the
(1987). They find that the number of retroreflector sets contributing to the return signal from a given single laser pulse can only be 1, 2 or 3.5, and give the computed pulse shape in each of these 3 cases. The laser used in their simulation is gaussian in profile, of standard deviation 33 ps. From cross-section's
the published profiles, we can infer the spread distributions, consisting of lidar and dista.nccs from spa.cecrMt ccntrc of grltvity. We now have the informa.tion
required to ca.rry out a convolution with our system signature, in the same way as for Lagcos. Wc assume that the rapid spin rate of Ajisai, of 40 rpm (Sasaki and H,'Lshimoto, 1987) will ensure
that
convolve
for cvcry
our
pass
system
all 3 possible
signature
with
orientations
each
of the slitellite
of the spread
will be sampled.
distributions,
and
sum
the
Wc thus resulting
3 distributions. The
results
of the simulations
3(a) and (b), where butions, also shown convolving
our
and
Ajisai
the quoted standard deviations on the plots. For completeness
system
o
for Lageos
scpaz'ately
60
_' --
'
with
I '
each
'
of the
'
'
are shown
in histogram
form
are those of the fitted Gaussian distriwc also present in Figure 3 the result of 3 orientations
I '
'
of Ajisai.
'
'
o" =
17
.__ I
I
I ' mrn
1
-
©
40
--
20
--
0 0
,_a _. --
0
__L_ Figure
3.
(a)
SimulaLcd
2-5
L_gcos
in Figures
rangc
residual
distributions.
of the
SPAD detector is essential to avoid Resolution of this problem awaits further 3.
Satellite
We now
Signature
take
as our
shown in Figure convolution with of cross-section
the rings,
standard,
paa'aaneters
spacecraft-centre of known
of non-uniformity
within
the
chip.
Models. single-photon
1, and develop from the spread functions
orientation, presented orientation, the lidar strength of returning
possible effects experimentation.
based
system-signature
it models of Lageos
upon
the
of expected and Ajisai.
row-by-row
fax-field
calibration
distribution
satellite return signatures, by For Lageos, we take the model diffraction
pattern
tests
in polar
in Fitzmaurice et al (1977). The parameters give, for the particula_ cross-section and number of corner cubes, in rows, contributing to the signal. Also given is the opticM distance of each row of reflectors from of gravity.
distances
from
We use the
centre
the
effective
of the
cross
satellite,
system signature with that of Lageos. In this estimate we ignore the effects of changing polarisation, which
section
to cazry
of the
cubes
in their
a convolution
of our
of the returning the amplitude
pulse of the
out
of the shape mainly affects
convolved pulse, and not its shape (Fitzmaurice et al 1977.) To model the return signatures from Ajisai we use the results of a computer simulation carried out by Sasaki and Hashimoto (1987). They a given single these 3 cases. 33 ps. From cross-sections
find that the number of retroreflector sets contributing to the return signal from laser pulse can only be 1, 2 or "1.5, and give the computed pulse shape in each of The laser used in their simulation is gaussian in profile, of standard deviation the published and distances
required to carry We assume that ensurc
that
convolve our 3 distributions. The 3(a)
profiles, we Call infer the spread distributions, from spacecraft centre of gravity, gTe now
consisting of lidar have the information
out a convolution with our system signature, in the same way as for Lageos. the rapid spin rate of Ajisai, of 40 rpm (Sasaki and Hashimoto, 1987) will
for every
pass
system
all 3 possible
signature
with
orientations
each
of the
results of the simulations for Lageos and (b), where the quoted standard
butions, also shown on the plots. convolving our system separately
of the satellite spread
mad Ajisai deviations
For completeness with each of the
will be sampled.
distributions,
axe shown are those
and
sum
in histogram of the fitted
we also present in Figure 3 orientations of Ajisai.
the
Wc thus resulting
form in Figures Gaussian distri3 the
result
of
01
o
60 a
=
17
mm
l> 0
z
4O o 0 I.-,
,.o
20
X; 0
-_
Figurc
3. (a) Simulated
2-6
I
I
]
I
Lagcos r,'mgc rcsidu'al distribution
I
5O
6o
=
(_)
23
(b)
mm
'u
=
30
5O 40
_, .o
4o 30
,> o
30
2O ,,D
E
10 lO
20
30
20
dO 140
5O
I
'
'
'
'
I
'
'
(c) II
' _r
' _
I
'
'
33
'
I
30
'
'
'
'
I
(a+b+c)
I
40
....
1 cr
=
20
120
40
I00
.2
30 0
O0
'
"5 GO ,-, 20 E
,10
1o 2O
20 Range
30 Residual
Figure
3.
20
40
Range
(cm)
(b)
Simulated
Ajisai
2-7
range
residual
distributions.
30 Residual
40 (cm)
'
3.1
Discussion.
The
standard
deviation
mean of 1.8 cm, The underestimate
neglect of atmospheric the satellite, and the Ajisai well
return with
of signature satellite
photon
data
deviations
results.
with
pass
orientation
Multi-photon
(1.7 cm)
is close
There
of between
is some
circumstances,
which
or orientations
2.3 and
evidence
discussion pulse
is based
upon
to be a random distribution
Observations
Experiments
and
were
in received levels was beam and
carried
may
for a given
with
return
event that
energies
be due
ground
to filter
observations
the experimental passes are shown in histogram Gaussian distributions. We calculate
the average
taken
out using
Ajisai
since
from a population response.
it is relatively
them to solve for corrections did not remove all trcnds biases which into a number
compare
observations
to the
dominance
of of a
of true
photon
level;
the detected
formed
by the convolution
We now consider
the effects
in order to quantify the variation of the mean
in each
easy
range
a large
to the predicted orbit. from the range residuals,
However, it was indicating the
segment
separately.
The
resulting
return
rates
at intervals
scatter
plot
each of the deviations
of 30 seconds
throughout
returns and the numbcrs of pre-rct_rn per second, the true percentage return
measurements*100)/(30*10
that such
in several of the 30-second intervals the calculated return levels we cannot reliably estimate the mean
may
be fax in excess
16 estimated
for
a near
used these 30-second mean values to estimate the mean the observations in our 6 segments, and these averages
2-8
for one
- number
of noise
return number 100%
rate.
of
six segments of the fitted
the noise rate in
events)
On the assumption that the quantum efficiency of the SPAD is 20%, we calculate corrected return rates the average numbers of photons in each return. However
of the
variation
from single photon to multiple photon by altering the divergence of the laser The observations wcre filtered in the
is shown in Figure 4. The residuals from form in Figure 5, along with the standard
percentage
to obtain
varied during the passes. We found that it was (G) of segments, and use the processing software
passes by counting the numbers of satcllite detections. Given that the laser fires 10 shots each 30-second interval is then (number
Ajisai
reduction.
of systematic range to divide each pass the
fading induced by The models of the
track.
at the single
of the satellite
encrgy from the large target. The variation achieved during the expcrimental passes hence the energy density at the satellite.
standard way, by using found that this process presence necessary
observational
3.3 cm, which
in the
of a larger number of photons reaching the single-photon detector, subsequent systematic effects caused by a signal-strength-dependent reflection distance to the satellite. 4.1
to our
and observed histograms is similar. may be attributed to various causes;
Returns.
is considered
of the laser
give standard
observational
particular
The foregoing
Lageos
turbulence (Gardner, 197G); neglect of coherency single satellite orientation chosen for the model.
signatures
the
variations
4.
of the simulated
and the appearance of the simulated of the observed scatter by our model
from these we found
rate was nearly 100%. At of returning photons, which Where
possible,
numbers of photons are shown in Figure
we have
contributing to 5. For those 2
m
1
I
r
(cuo)
l_np!so_l 2-9
a+u+_I
140 ....
I''
120
n
=
''1''''1
....
]''
6
o"
''1'''
=
20
F
mm
I00
I00
L20
n = 0
o = 20 mm
;
OO
• N 6O ,o
_
4o
40
m
2O
_
,I,,,,1 0 -1_
,
,
,
,
I
, .-
,
,
-5
-I0
0
[_ lO
0
15
__Ji--L-L_/_[_L
-15
140
• ,
-lO
-5
,
,
J ,
0
,5
I0
I ....
I ....
I'''
i
I
I 15
14Q
....
I ' ' ' ' I r'T-m_]_ ....
I ....
''''l
I ' ' °
....
I ....
J
P'O
I00
n _'[_
ll_ 1
a = 13
I00
(r = IG
O0
z
Jl /% IG
120
F--
40
2O
2O I--
60
o
0 -15
"-..- 10
-5
0
fi,
10
15
JJ-J-J_
-15
14OL_ 120 140f_
_Lj_j_I"
120L
J--LLLL -10
°
'
'
1_
I
=
-to
....
I
0
*
'
'
'
I
'
'
'
'
i
' In '
=I
' 15'
*
'
I
'
'
'
'
I'"_
'
'
'
it= I '
' 16'
'
I
'
'
'
'
'
t
'
'
'
"T
,]
=
18
--_
'
100
lO01--
00'
w o
'
15
fJ o"
'
LLLL_ lO
b
"
N
GO
_
4o
60
4O
2O
20
.... 0
,,,,1,,,,
0
-lg
iO -iO
Figurc
I,,,,i
,1,
5.
-5Range
0 Residual
15
-15
( cn5 0
Distribution of reazgc turning photons.
rcsiduMs
from
2-10
Ajisai
pass
-IO
as
-5 Raw8©
,_ functioll
0 Residual
of
5 (el
avcragc
,0 numbers
10
15
n of x','-
_=
segments
where
the
average
return
photons
as >16,
but
remark
that
4.2
Model
There
and
of the
satellite
variation
of histogram
signature
remains
resemble
results
ta_uce during corrections. change model
cannot
those
numbers
we have
could
asigned
be several
the
times
numbers
of
as large.
shape
and
single-shot
Starlette
to detect
precision
returns, 1). For and
or ERS-1
a systematic
the
change
the distribution the high return histograms
(Figure
variation
with
of signal
of residuals rates little
qualitatively
distance of the of the
50 ps, to represent a random number
and
1). of satellite
mean
reflection
the passes, because the method of reducing the observations absorbs However we can use models to predict both the increase of precision
by convolution
FWHM we use
100%,
in the distributions,
from
be used
of mean reflection the time-distribution
number,
true
near
At low return rates equivalent to single photon to the 'standard' Ajisa.i distribution (Figure
quantitatively These
the
were
Discussion.
is a clear
strength. is similar
rates
dis-
any such and this
as a function of numbers of photons in each return. We returning photons, from which we may sample a variable
Ajisai
spread
distributions
the laser. To model the effect generator to pick one 'photon'
with
a Gaussian
distribution
of n photons reaching the from our time-distribution
of
detector, of pho-
tons, then reco1"d its time-location within the distribution, and repeat the process n times. We then sort this sequence of n relative event times into chronological order of arrival at the detector. time dom event the
We model
the
20% efficiency
of the
detector
by stepping
through
the
n events
in
order, at each step generating an integer ran(lore number in the range 1-5. If the rannumber is 1, the event is accepted (detected). If the random number is not 1, the next is 'tested'. selection
In this way
of a single
wc generate
photon
from
a large
a series
number
of returns
The mean and standard deviation of these event in cm. The standard deviation values are added
of event containing
times
each
an average
resulting
from
of n photons.
times arc computed and converted to range quadratically to the estimated system jitter
(0.8 cm) to fully model the observations. The results of simulations of range precision and biases from Ajisai for values of n between 1 and 50 arc shown in Figures 6a and 6b, where the results hnye bccn joined by continuous lines. The 30-second aver_Lge observed values of precision, where they Ajisai passes, are shown predicted distance
range bias curve from the satellite
reaching the detector from the finite pulse strengths change 4.3
at the
in Figure 6b expresses the expected change centre of mass as a result of increasing the
in each laser return. Most length of the laser (FWHM
single
is predicted
Lageos
photon
with
level
increasing
Centre-of-mass
We can
use
Lageos,
in the
Figure number
can be reliably cstimated (see section 4.1) from our experimental as dots on the graph and agree well with those predicted. The
the
above context
of the change of the 1.3 cm for a variation
of about
of photons
40 photons
beyond
that
a contribution between signal
per
return.
Little
point.
correction.
techniques of worldwide
6 shows the results of photons reaching
of the bias, which contains 50ps), is seen to take effect
up to an average numbers
of mean reflection number of photons
to estim_Lte SLR
the
systems
magnitude working
of a systematic at different
range-bias
return-signal
of a computation of the rmlgc bias as a function the detector, for 2 modelled laser pulse-lengths. The
effective reflection distaalce from of return level fl'om single-photons
2-11
the
satellite centre to the 40 photon
for levels.
of avcragc magnitude
of mass is about level. This result
zl_'-'l--*l
I I
I
_I
l
I
I
I
l
I
l
i
i
i
i
i
I
i
i
i
i
i
i
i
i
I
3
•
++ b
a)
Ajisai
i
_(a)
Prcdictcd
lind obscrvcd
bcrs of photons |
0
l
'
J
I
variation
of Ajisai
range
prccision
as a function
of avcragc
num-
rcccivcd. ]
]
0
|
l
J
,
]
I0
, ....J
,
,
t
20
,
,
i
J
30
I .J
,
J__.a__
40
50
4
-
B v
(b)
Ajisni
2
o
o (.9
_eeith
)
munbcrs
of photons
for Ajis+d.
0
-1
, 0
',
,
,
J
"-+.
I
f
,
,
I0
I
,
j
,
,___]
,
,,
j
30
20
1
,
,
,
L+
40
50
2
I
B v
laser
50ps (c)
aageos
£
o
o ¢.) ,NmnV._. COUNTER COMPUIER
DELAY GENERATOR Figure 3 Portable Standard Hardware (SLR Configuration)
2.1 Frequency Source A Hewlett Packard Cesium beam standard with a high-performance option tube and an Austron disciplined oscillator provide the frequency source for the PS. The disciplined oscillator improves the short-term frequency stability an order of magnitude when compared with use of the Cesium standard alone. 2.2 Time Interval Measurement Several HP5370 (A & B) time interval counters and two Stanford SR620 time Interval counters are available to take range measurements. The time interval counters are arranged to take multiple measurements of the same event to Improve the data quality. These counters can also be configured to measure differential time (figure 4) between two return events or a combination of events depending on the application. For these first tests 4 HP5370 counters were used.
4-3
I,ll]ql
J
_ULEH(_II4
l
!
LMI_
OPTICAL DEIECTOR #1
WAVELENGTH SEPARATOR WAt_JE_alH
#1
I_ACNSTANT
"nON
I
I
CRIMINA'TOR ]_ I
I
"nuE IL. I I COUN R il I
VARIABLE
IN'IERVAL
OPTICAL DE'lECTOR #2
L
DIGITIZER
It°"
IN'IERVALcouN11ER I
PHOTODIODE IN'IERVAL ,=I> IFRACTION I [DISCRIMINATORJ PRIMARY START PULSE
ICONSTANT
I
COUNIER
IFRACTION I IDISCRIMINATOR j IDIFFERENTIAL IRANGE AND PULSE 'AMPUTUDE IMEASUREMENT
I
TIME TIME INTERVAL COUNTER
r EPOCH TIME-TAG -dl>
I I
INTERVAL COUNTER
]M]EASA_ ]lL,M_,ze
Figure 4 Differential
Range Configuration
(Two Color etc)
2.3 Signal Processing A Tennelec constant fraction discriminator (TC-454) is used to process the MCP-PMT detector output. The discriminator is calibrated to remove systematic amplitude-dependent errors (time-walk). For these first tests the MOBLAS-7 discriminator was used and no amplitude measurement was made using the PS. 2.4 Optical Detection The PS features a detector package which can accommodate several detectors. These may be directly coupled to the optics, or indirectly using fiber-optics. During two-color ranging experiments two MCP-PMT's may be used to separate the wavelenths for differential time measurement. Other types of detectors (PMT, APD, Photodiode) can be used depending on the application, or simultaneously for detection Intercomparison. During the first series of passes the MOBLAS-7 MCP-PMT detector was used. 2.5 Amplitude/Waveform Measurement The output of the MCP-PMT may be digitized using a Tektronix 7912HB (1 GHz bandwidth) digitizer from which amplitude information is extracted. This information can be applied to the range measurements to correct for discriminator time-walk. The digitizer can also be configured to measure the differential time between two pulses while the entire waveform record of each shot is stored on disk. During the TOPEX measurements, a 4.5 GHz bandwidth digitizer coupled to a 60 GHz bandwidth photodiode was substituted for the normal digitizer to map the optical response of the TOPEX array segments.
4-4
2.6 Environmental Instrumentation The thermal environment of the PS instrumentation is monitored and stabilized using microprocessor controlled fans. Thermal sensors are arranged to measure the temperature of the air discharged by the instruments. Thermal stability can be maintained better than 1 degree Centigrade depending on the airconditioning system available. Thermal stability is essential to maintain high data quality. 2.7 Calibration Optical calibration provides a means to model Time Interval Meter non-linearities for limited dynamic range measurements such as satellite laboratory characterization and two-color differential time interval measurement. The optical calibration mechanism (figure 5) consists of a diode laser, optics and a computer-controlled microposltioner with ~ 2 _m precision. A pulse emitted by the diode laser is split into two pulses, one pulse travels a fixed distance while the second pulse traverses a known but variable range. The two pulses are each detected by a common detector and the signal processed using a common discrlmlnator. The calibration mechanism may be used two ways. For discriminator (amplitude-dependent error) calibration the separation between the pulses is held constant, while the amplitude of one of the pulses isvaried using a neutral density filter wheel. A real-time histogram of the varied pulse height is displayed on the computer CRT assuring that a good distribution of data is collected to determine the CFD time-walk curve. For range-dependent error, the amplitude of each pulse is maintained at a constant value, while the pulse-pair separation iSvaried. A number of data values are collected at each range Interval. The variation in separation step size and number of points per position is selectable and Is dependent on the desired accuracy. For LAGEOS-2 measurements 0.25 mm instrumental accuracy was desired so an appropriate step size and data volume (500 measurements/position) were used. DIODE LASER
LASER PULSE
CUBE CORNER
DIODE LASER PULSE PAIR
,2)-f (Xl)
O-R(X1)+
Ob-T(X1,)_2)
(2)
Where -_ T(X2)-T(X1)
5T(X1,X2)
2 (3)
°o'-r 0,_,>,2) = i=1
AT (X i) nph(Xi)
• T/qE(), i )
Absolute
range
sweep
to the satellite
RO R(X)
= =
f(X)
=
Dispersion
TO
=
Absolute
time
T(X)
=
Increase
in time
Measured
" A
range
at wavelength
),
factor
at wavelength
of flight of flight
s(x)
=
r/ph
=
_QE
=
Pulse profile factor Number of photons Photocathode quantum
A
=
Microchannel
5T
=
(7
=
Differential time of flight Standard deviation
AT(X)
=
Pulse
width
5-39
through
),
coupling
at X
efficiency factor
atmosphere
DATA ANALYSIS
SMOOTHING
TECHNIQUES
(3 POINT) ALGORITHM
( a(m-l)+ b(m-1)+ ¢(m-1) ) (m-=)
(4)
( a + b + c )
I b(m-1)+
(m) =
c(m-1)l
(s)
(b+c)
I a(m-l)
(m) =
.
b(m-1)
) (6)
(a+b)
m
Mean intensity "m" iterations
a,b,c
Weighting
of the pixel at location
coefficients
DETECTION:
Peak Half Maximum Centroid
(Mean Value)
5-40
p after
ORIGINAL BLACK
AND
WHITE
PAGE PHOTOGRAPH
LLI I--" Cf) >-U3 LLI > LL] (._) LLI (3£ rY _J CO CD LL] U3 CIJ < (3£ L_J r_ W W
n-uj 13_ n," (__ WO')
_w ,_.J
oN rY w I--m_
0 Lh
O_ w
w_ (.)Z w __1 0 i_. I--
o_ 5-42
5-43
l,
o rY i__jo _o,J
D_
5-44
|
m_
C
+++ ++ I.,x+Oo_.
+g
o
i
i'
i
o
:
0
:m--+++,+,_,_+,_ ('13XId/Sd)
a33dCj
d3"-JMS
("FIXId/Sd) a:13clScl33MS
5-45
SUMMARY Single photoelectron sensitive streak camera SLR receive system has been configured with a resolution approaching 250 fs/pixel for high accuracy atmospheric dispersion measurements. It has been verified that the streak camera timing characteristics are profoundly impacted by the sweep voltage. The sweep voltage is intrinsically nonlinear in the leading and trailing edges and must be corrected using optical calibration to achieve picosecond timing accuracy, centroid and half maxima (mean) analyses were found to be superior to peak detection. Real-time calibration has been found to be very effective in monitoring the timing performance and would be very advantageous for critical timing measurements.
5-46
N94-15574 THE
FIRST
SATELLITE
RECORDED
ON
THE
K.Hamal, Faculty
of Nuclear
Phone/fax
+42
Science Brehova
2 848840,
LASER
ECHOES
STREAK
CAMERA
I.Proch_ka
and Physical Engineering, Czech 7,115 19 Prague l,Czechoslovakia,
telex
121254
fjfi c, E-mail
G.Kirchner, Austrian Academy A-8042 Graz,
Technical
University
[email protected]
F.Koidl
of Sciences,Lustbuenel Austria, Phone +43
Observatory 316 472231
ABSTRACT The application is described. The integrated ranging ed.
of the streak camera with the circular sweep for the satellite laser ranging Modular Streak Camera system employing the circular sweep option was
into the conventional has been
Satellite
performed.
The
Laser
System.
first satellite
The experimental
laser
echo
streak
satellite
tracking
records
are present-
camera
and
GENERAL The laser
ranging
is an attractive
and
is gradually requested accuracy.
at 532
unit
between
reaching
millimeter the
wavelength
The
laser
level
and the long ground
ranging
precision
at present.
The
baselines
and
accuracy
for
nineties,
goal
that
is the
millimeter goals
to predict
ranging
propagation accuracy.
main
However,
to
The on
two
obtain must
the
camera
detectors 5--47
the
time interval
centimeter
to
meters
and
time interval error
and hence
models
with centimeter and
atmospheric valuable
electronic
from
atmospheric delay
wavelength
be measured
as a return
_.
to the systematic
optical
the existing
An
improvement
existing
millimeter of 20-200
photomultiplier
to determine
and discriminators,
of a streak
of the existing
detection
accuracy
the atmospheric
delay
is used
contributors
atmosphere.
simultaneously
of the implementation
: the replacement
The
time difference,
the two wavelength
signal
systems
used detectors
itself.
plate
photodiode
of 30 picoseconds.
picoseconds
and echo
microchannel
or an avalanche
resolution
of 20-35
for the current
accuracy
the fast
discriminator
interval
transmittion
factor
data permit
improvement, first
fi time
of the target final
It is expected,
The
the Moon
centimeter
as a transmitter, electric
level are the currently
meteorological
The
satellites,
technique.
one
a resolution
pulse
limiting
the contribution
to
nanometers
having
the laser
The
limiting
developing
it reaches
with an appropriate
detector
interval
Earth
by the data users, is the satellite laser ranging to artificial satellites with The existing pulsed laser ranging systems are using short pulse lasers
along
signal
rapidly
increasing,
picoseconds tube
of the artificial
data
determining
models for
into a laser
on
the
two
will be improved atmospheric
with picosecond
and discriminators
based accuracy.
ranging
model
accuracy system
by the streak
2 . : camera
with and appropriate readout and data processing system. This will increase the time interval resolution of the radar detection chain several times, the echo pulses distortion by the target geometry may be monitored and compensated. The second : the streak camera will be used for two wavelength laser ranging echo signals detection, the two wavelength range delay may be determined with the picosecond accuracy. The third : along with the detector, the streak camera may be integrated into the time interval unit. The picosecond time resolution and a high overall timing accuracy is expected I. THE STREAI_
CAMERA
CONSTRUCTION
Designing the streak camera for satellite laser ranging purpose several key problems to be solved: energy budget of the ranging chain, closely connected to the photocathode and sweep used, camera configuration, the type of deflection, input optics configuration, readout system and the output data processing. Completing the series of indoor and ground target ranging experiments, we have chosen the $25 photocathode, the circular sweep camera setup and a two dimensional TV readout system with a full frame image processing. "l'be linear sweep tube setup reaches higher limiting temporal resolution. However, the necessity of a trigger signal appearing 1030 nanoseconds prior to the photons to be detected with a subnanosecond jitter and the angular/temporal relation may cause serious difficulties when ranging to satellites. Using the circular sweep tube setup, the trigger signal requirements are moderate : the trigger signal must appear 10-20 microseconds before the optical signal, the jitter of several microseconds is acceptable. The temporal/angular dependence may be monitored, software modelled and compensated. The PV-006 streak tube having the $25 photocathode and the microchannel plate image intensifier fiber optically coupled together have been used. The streak tube is equipped with two pairs of deflecting plates acting in the mutually perpendicular direction. Applying the RF signal phase shifted to both deflection plate pairs, the circular sweep may be obtained. The 320 MHz signal, 13 Watts of pulsed RF power is used. The maximal RF power applicable on the deflection system is limited by the internal ionization inside the tube. The diameter of the circle was about 6 mm resulting in 155 psec/mm sweep speed. Due to the imperfect impedance matching of the RF driving circuit to the tube deflection system, the deflection is not perfectly circular. Nevertheless, the complex streak image processing and calibration package is able to compensate for these effects. The temporal resolution of 30-35 psec and the range difference jitter 6 psec have been achieved. The application of the streak camera for ranging purposes is accomplished by the timing and gating circuitry. The deflection signal is ON for only few microseconds before laser transmittion and again few microseconds before expected arrival of the satellite echo. All the remaining time the camera is working in the static image mode and may be used for guiding / alignment purposes, as well. The 320MHz deflection signal is produced by multiplication of the 5 MHz sine wave output of the station Cs beam frequency standard, which is simultaneously acting as an master oscillator for all the station timing electronics. This way, the precise phase synchronism of the radar electronics and the camera circular deflection is maintained. In fact, the camera may be used as a vernier to the time interval unit, rough time interval is derived from the integer number of periods from Start to Stop event, the fraction of the period may be determined from the phase difference of the Start and Stop even_. The microchannel plate intensifier gain is controlled in three steps. During the laser have - the speed - the - the
5-48
transmittion,
the
atmospheric
is set
backscattered
photocathode promise
gain
is used.
between
minimum
light.
Most
the static
to avoid
Optionally,
of the time image
expected echo arrival time, achieve maximum detection To readout
to
the
the
mechanical
mode
plate
system of
by
a com-
contribution.
for 300
Intensified
the
the input
is set to 100,
noise
of 10,000
we use the Silicon
the
in front
gain
gain and the background
image
of
shutter
the microchannel
the gain is set to maximum sensitivity.
the tube screen
blinding
At the
microseconds Target
to
(SIT)
tube
made by Haimann. The output signal was fed to the Visionetics Frame Grabber card (512x512x8bits) inserted in the IBM PC. To solve the problem of a deflection nonsymetry, the software
package
3 allows
the full frame
image
processing
and
accomplishes
the software
modelling of the image distortion, the sweep nonlinearity, the gain nonuniformity etc. On the end of the image processing procedure the temporal curve consisting of 1000 channels, 8 bits each
is generated.
satellite
image
Once
to install
SATELLITE
Lustbuehel laser,
design
streak
RANGING
Observatory,
passively
mode
locked
been Austria.
NdYAG
The
in green.
containing
60
may
milliJoules
returned
photons
package
based
ranging
on a single
hard/software
photon
remained
+ 5 C what
system
using the
compensated.
with its low
mass
telescope.
Ranging
consists
harmonic
be transmitted.
the The
System
of a modified
generator, semitrain
the
Quantel
delivering
pulses
of 5 - 7 such pulses
telescope
is a Contraves
laser
ISIT camera attached to the telescope and dielectric mirror is directing 99% of the
the remaining
avalanche
unchanged.
photons
photodiode. Thanks
enter
All the
the standard
rest
to the photodiode
of the
in significant
dark
noise
detector
satellite
single photon
ranging capability has been preserved, although system timing and gating logic has been added. image intensifier and the readout have been
resulted
of
by a 10 cm diameter Galileo telescope, the 0.5 for both return photons collection and visual
photocathode
capability, the satellite routine return rate. The streak camera The streak tube, the temperature
ranging
replaced an original visual tracking. The
on the streak
along
Satellite
Alternatively
tracking type. The laser output is transmitted meter diameter Cassegrain optics is used The streak camera for faint objects
to the
with the second
35 picoseconds
guiding. dedicated
may be software
construction
part of the tracking
integrated
of 10 milliJoules, totally
for example
SYSTEM
has Graz,
is identified,
effecP
its rugged
on the moving
camera
circle
the temporal/angular
of the camera,
it directly
LASER
The
of the deflection
in the static mode,
The compact permitted
the center
laser
response
with
reduced
kept
at
the
reduction.
RESULTS The have
been
been km,
retroreflectors ranged.
obtained see Figure
The
January
equipped first
satellite
18,1991
1. In this stage,
satellites laser
at 21:37
at the distances
ranging UT from
the semitrain
echoes
of
the AJISAI
of pulses
1,000
recorded
satellite
separated
is near
the
center
of the pattern
displayed
in the
static
kilometers camera
have
at the distance
2000
by 8.557
been transmitted. On the image the time interval of 40 milliseconds transmittion to echo detection is integrated. The transmitted laser image
to 2,300
by a streak
nanoseconds
has
covering the laser beam backscattered
pulse light
image.
moment
the
was not illuminated by the Sun. On Figure satellite echo obtained transmitting single
energy. camera
The temporal profile of the firs part of the trace is included. Please, note the streak receiver system saturation by the strong echo signal coming from the first rows of the 5-49
2 there is a streak picosecond pulse
At this
satellite AJISAI
camera record of the containing 10 mJ of
corner
reflectors.
retroreflectors.
The
the time interval echoes
coming
nonlinearity
about one nanosecond
depending
backscattered
light
satellite
echo
record
satellite
is a sphere
detector
various
illuminated
comparison
retroreflectors
compensated
has been covered
3. The
satellite.
may be seen.
response
from
be clearly
time
profile
temporal
corner
sweep
speed
spot is an static image
of
The atmospheric The
of about
STARLE-TFE
transmitted.
The
25 centimeters
is significantly
of the echo
resolution
reflector
The separate
The
has been
spread
with
orientation.
shutter.
pulse
covered
be spread over
of the sweep.
mechanical
signal
The temporal
a single
central
of the diameter
echo
The system
The
the center the
meters should
distinguished.
picosecond
with retroreflectors
kilometers.
to the AJISAI
out by Single
two pulse
on the satellite
may
thus marking
blocked
is on Figure
exceeding
the returned
on this display.
by the Sun,
1,000
saturation
not saturated
of diameter
simulations,
from
about
is a sphere
to numerical
has not been
the satellite
distance
satellite
According
is included,
as well.
may be demonstrated
resulting
in a pulse
on the streak
camera
at a
smaller
width
in The
on the of 25-30
picoseconds. CONCLUSION The first satellite for
the
circular camera ranging
first
time.
sweep
laser The
for satellite
has been
echoes laser
confirmed
employing
have been
applicability
recorded
of a Modular
Streak
has been
demonstrated.
ranging
to be satisfactory
available
laser
ranging
Camera
to our knowledge
system
employing
The sensitivity
for the purpose
: for standard
the
of the streak
geodetic
satellite
technology.
REFERENCES
1. J.J.Degnan, "Satellite Trans.on Geoscience and 2. J.Abshire, 3.
Applied
P.Valach,"
Laser Remote
Optics,
Streak
Limitations", Antibes,
Sept. 1986,
5. K.Hamal, for Ranging", Photonies,
proc.
edited
presented Cambridge,
Frame
Ranging
"Streak
of the Sixth
I.Prochazka,
Full
on Laser
K.Hamal,
Current Status and Future Vol. GE-23,pp.398-413,July
Vol. 19, No 20,pp.3436-3440,
Camera
International Workshop C.Veilet,CERGA,France 4. I.Prochazka,
Ranging: Sensing,
Camera
Image
International
Radar
Workshop
V.Lozovoi,
at the 19th International UK,Sept.
proc.of
17-21,1991,
5-50
the
Oct.1989,
Receiver,
on Laser
by J.Gaignebet,Cerga,France, M.Schelev,
IEEE
1980 Processing",
Instrumentation,Matera, as a Laser
Prospects', 1985
Seventh edited
its Performance
Ranging
by and
Instrumentation,
1987 V.Postovalov,
Congress published
" Modular
on High
in SPIE
Speed
1358-55
Streak
Camera
Photography
and
SATELLITE
LASER
FIRST STREAK
AJISAI
satellite,
RANGING
RECORDS
diameter
2.,
meters
range 1 500 km January 19, 1991 , UT 21:37 0
v
C= O
% an
sweep
dk
period 3.125
nsec, displayed
part 1 nsec
Fig.
5-51
1
...... r
"_
q
•
fiJI_lI
satellite
" q, lb
• •
IN
Q
picosecondlaser pulse response on streak
i88
?5
58
25
8
t
1
!
188 24B 68 128 fine [ 5 psec/pixel : 1,5 nsec/screen ] 5-52
Fig.
2
SATELLITE
L,_ SER RANGING
FIRST STREAK
STARLETTE
satellite,
RECORDS
diameter
0.3
meter
range 1 000 km January 24, 1991 , UT 21:59
100 psec 15 mm range
t -_.J
n --
•-41.
r_ _
_
.,11...,113__
.,S'Cn r'__
,.r-,..,n_r_ .IL,qn_
echo signal temporal
profile
8 psec / pixel
Fig. 5-53
3
Calibration Techniques/Targets
N94-15575 Experience
and
Results
of
the
1991
P. INSTITUT
MTLRS_I
Campaign
SPERBER
FUR ANGEWANDTE
FUNDAMENTALSTATION DER
USSR
FORSCHUNGSGRUPPE D-8493
GEODASIE
WETTZELL SATELLITENGEOD,_SIE
K()TZTING
H. HAUCK INSTITUT
FUR ANGEANDTE
RICHARD-STRAUSS D-6000
GEODASIE
ALLEE
II
FRANKFURT/MAIN
70
Abstract. In the fall 1991 the Modular, Transportable Laser Ranging System MTLRS#I was operating in the USSR for collocation of the SLR systems in Riga, Simeiz and Kazivelli. In this paper we will summarize the results of the collocation experiments and we will show our (positive and negative) experiences,
1.
we got during this campaign
in the USSR).
Introduction
The
year
upgrades
1991
Germany)
and
MEDLAS
nor
After
MTLRS#2
MTLRS#I)
upgrade
was
and
by
operated
the
OSG
to
(about
in the first
Due
half
out
SLR
system,
two
fixed
SLR
scheduled
by the IfAG,
neither
(P. Sperber
sites in
the
a WEGENER-
in 1991.
of 1991
at two
to
(operated
Netherlands) carried
fixed
the
3 km
was
systems. MTLRS#1
Kootwijk,
maesurements
the
to collocate
ranging
Systems
campaign
to make close
laser
Ranging
of MTLRS#I
choosen
Kasivelli
mobile
Laser Project
in August
we
pad
for the
(operated Dynamics
Wettzell
Riga/Latvia
year
Transportable
a Crustal
from
MTLRS#1
2.
a special
the successful
departed In
was
of the Modular
in the
et al.)
Simeiz/Ucrainea
station
the system
USSR. the
in Simeiz
(300
place
for
m distance
to
distance).
Results An
overview
about
system
arrived
the
number
and
quality
of the
MTLRS#1
passes
is shown
in Fig.
1 and
Fig.
2. The new
parts
first
data
In
of the were
week
army
34
During
the
All
this
the
quantity
completely After sytem
faced
against
rest
with
(number
Because during
a problem,
our
we
Due
observations
of measurements are
32.
installed
gorbatchov.
to stop
problems
week
were
the the
crew
was
upgrade,
it
took
not
yet
before:
In
moscow
familiar
some
with
days,
some
before
the
successfully.
we were
we had
during
which
collected
putsched
situation
in Riga
system,
to again
in Riga
showing
in an
of passes
per
for nearly faced
poor
nor
had
unclear
we were
unusual
week)
never
the
the
and one with
dangereous
of the and
soviet
military
week. extremely
performance quality
parts
political
of
(number
bad
weather
MTLRS#
1 in
conditions.
Riga.
of normalpoints
per
Neither pass)
was
moved
the
satisfying. 43
Lageos
passes
we stopped
the
observations
in Riga
on
October
3 rd
and
to Simeiz. Typeset
6-1
by .AA,t-q-TEX
Here the system was able to show its habitual performance. After 53 Lageos passes with more than eleven normalpoints per pass in average the campaign was finished on November 23 rd. The computation of the collocation was performed by the computing Frankfurt/Main. The results are summarized in Fig. 3 - Fig. 5.
center
of the
IfAG
in
Fig. 3 shows the results of the Riga collocation. We got 16 simuitaneos Lageos passes with a R.M.S. of 20 cm at the Riga system and 1 cm or 2 cm at MTLBS#I depending whether a PMT or a single photon avalanche diode (I. Prochaska et al., P. Sperber et al.) was used as receiver. Out of this 16 passes six passes with good residual overlap (for example: Fig. 4) were selected to calculate the range and epoch bias of the Riga SLR system. There is a small negative tendency in both biases, but compared to the error values and the R.M.S. of the Riga system we can't find a significant bias. Fig. 5 summarizes the results of the collocation in Simeiz. Because of problems, the fixed stations only were able to observe few passes during the collocation, but all of the passes were simultaneous with MTLRS# 1. The data of the fixed stations was not possible. 3.
are not yet delivered
to the network,
so until now a computation
Experience
In this chapter we will summarize our experience of a dedicated geodetic system in the USSR. 2.2.
Operation
during the on-site
operartion
and the transport
on stations
From the operational point of view there were no problems as long as the system was working near stations. All our requirements concerning electrical power, safety, infrastructure, etc. were fullfilled. In Riga also the supply of fuel and the hotel accomodation were satisfying. On all stations an independent communication facility like Inmarsat is necessary. The only local data channnel is a very unreliable telex line. In Simeiz,
the hotel,
food and fuelsituation
•
A hotel near the station km away.
•
For fuel a big spare
•
As there
Additionally
is far under western
tank is necessary,
are no restaurants
most of the people
is very inconvenient:
because
near the station, only speak
russian
standard,
an acceptable
fuel is not always facalities
Transport
During compared
between
than 40
available.
are needed
to prepare
own food
language.
In spite of this problems, the operation of a sir system near fixed stations some preparations are made to facilitate the life of the crew members. 2.2.
one is more
is always
possible,
if
stations
the transport of a system from one station to the operation on stations. channels
to foreign
are not available
in short
becomes
very bad
•
Communication
•
Hotels only exist in big cities. Sleeping facilities for all persons in cars (caravans) are strongly recommended because most of the hotels are full without reservation four weeks in advance.
6-2
countries
to the other the situation
time
•
Food is only available
•
Security
•
Fuel is not always availble,
•
Car repair is possible,
The poeple
is a big problem,
only speak
to help if there 3.
in hotels,
so there are facilities
day and night guards therefor
necessary
are absolutely
big fuel tanks are needed
but takes a lot of time and you should
russian
(or sometimes
german),
to cook in the cars. necessary. in the ears. have all spare
but are very friendly
parts with you.
and will always try
are problems.
Summary In the
second
half of 1991 the
collocate the fixed laser ranging The results of the collocation collocation in To operate regions of the from the local
MTLRS#I
was operating
stations on this places. shows no significant problem
successfully at the Riga
Simeiz is not yet computed. and transport a dedicated geodetic system like MTLRS#I USSR big efforts and preparations are necessary to become infrastructure.
6-3
in Riga fixed
and
Simeiz
slr station.
to The
in in the underdeveloped as independent as possible
REFERENCES
P. Sperber, L. Amberg, Upgrscle, 199t. I. Prochazka,
K.
Instrument&tion P. Sperber,
L. Beyer,
Kamal,
B.
S. 219,
U. Hessels,
R.
G. Blenski,
Sopko,
Proceedings
PAotodiode Motz
U. Hessels,
Bazed
in this
6-4
Detector
Proceedings,
11. Motz,
of
the
seventh
PackaEe The
in this Proceedings,
new
]or
international CentimeLer
MTLRS#1
Remlhj
Workshop Satellite
Receiver
ol the MTLR5#1
on
Ranglug Pscka#e
Laser , 1989.
199t.
Ranging
NUMBER
OF TRACKED
PASSES
14 LIGHT 12
!_
i-i
NIGHT
....n-m
_
ALL
II II
II
.... mm--
-
II
_
]
4
_1
10 8 6
J
1
30
32
34
36 WEEK
Fig.
1
Number
NORMALPOINTS
15
Lageos
40
42
44
46
48
IN 1991 Passes
in
Riga
and
Simeiz
PER PASS
LIGHT
I
of
38
E_J NIGHT
ii
ALL ]
36
38
10
oi i 0
I
i
1
t
30
_
_
32
34
WEEK Fig.
2
Number in Riga
-7-
40
42
44
46
IN 1991
of Normalpoints and Simeiz 6-5
per
Lageos
pass
48
Results
Riga
MTLRS#1
(1884)
15868
27166
Returns
R.M.S.
1 cm
20 cm Aug.
15 - Oct.
16 Simultaneous
Range in cm
Bias
7560-1884
Fig.
Returns (SPAD)
(43
Passes)
- 2 cm
(PMT)
10 Passes
Epoch Bias in microsec
7560-1884
-24 -30 -58 -23 -4 +66
-6.1 -2.5 -5.1 -16.3 -0.4 -8.4
-6.5
(7560)
cm +- 5 cm
3
Results
-12 microsec
of
the
6-6
collocation
in
Riga
+- 30
RANGE 030 .'"'1
....
I ....
RESIDUALS
I""1""1'"'1''"I'"'1
....
I ....
1'"'1
....
I ....
I ....
I'"'1
....
t'"'1
....
t ....
I .... -
r.
025 o
020
!!;,t T= tz rv bJ _J Lg Z H
z >
Ra
MILLIMETER SATELLITE
Figure 3: variables
Diagram used in
6 SATELLITE
of a spherical the analysis.
IMPULSE
RESPONSE
AND
geodetic
TARGET
satellite
the
SPECKLE
An individual retroreflector responds as a point does not spread the laser pulse in time. However, array of retroreflectors, the laser pulse arrives tion center" of each retroreflector at a slightly leading to a broadening of the received location of the "reflection center" for corner reflector is given by [Fitzmaurice
defining
source and hence with a typical at the "reflecdifferent time
pulse [Degnan, an individual et al, 1977;
1985]. The solid cube Arnold,
1978] si AR(Oi.c)=
nL
1-
_,c = nLcosOre/
(6.1)
where AR(0i,c) is measured from the center of the front face of the cube corner to the reflection point, L is the vertex to front face dimension, n is the refractive index of the corner cube material,
0_.c is
the
sponding
refraction
angle angle.
of
incidence,
From 7 -44
Figure
and 3,
it
0re/ is can
be
the
corre-
seen
that
a
cube at relative
an angle to the
station
(0inc =
0i,c to surface
0),
the of
given
incident wave the satellite
Rs
is
the
a time delay, to the ranging
by
At(0inc)=_{R-[Rs-_R(Oinc)]cosOinc}= C s
where
produces closest
l--c0s0in
satellite
radius.
It
should
e
l--EC0S0re
also
be
I
noted
(6.2)
that
the differential delay between target reflection points also introduces a random phase delay between individual reflectors. Thus, if the temporal profiles from multiple cubes overlap at the range receiver, the electric fields will interfere with each other in a random way from shot to shot resulting in target "speckle". On average, however, the return waveform from the satellite should behave as if each of the retroreflectors is an incoherent source. This was an implicit assumption in our derivation of target optical cross-section in Section 5. In the same spirit, the time-averaged satellite impulse response can be estimated by summing the weighted (incoherent) returns from each of the retroreflectors. Using the simple model for a spherical satellite introduced in Section 5, the impulse response can be shown to be
where
the
dO,._ sin
O,..q2 (O,._)6[t
geometric
weighting
(5.3),A/(0_,c)
is
given
by
5[t-_/(0Lnc) ] represents incident function
on is
factor
is
given
by
and
the
delta
function
(6.2),
an
the satellite. nonzero only
(6 3)
- At(O,._)]
infinitely
short
From (6.2), we when the condition
laser see
(2.4)
or
pulse
that
waveform
the
delta
I-T
cosO( , ,n)
(6.4)
= 1 -_+,
1 -6 holds
where
we
have
[co,oc. c,°,]2
defined
the
new
variables
ct 6 < T < T max
T --
2Rs
nL 6 -- R s
1 T max
The variable • is roundtrip transit center cube
and to
the
back,
= I-
C0S0ma
x
i-6
+
COS
a normalized time, expressed time from the surface of the and
satellite
e is
the
radius.
ratio
of
The
minimum
7-45
max
(6.5)
I -_
the
in units satellite
optical and
of the to the
depth
maximum
of
values
the of
are
determined
(6.4) the
and
by
solving
baseline,
From
setting for
is
(5.3)
and
expressed
as
_.
given
equal
The
by
(6.3), a
8
total
of
the
lite
diameters
defined
by
(6 _ 0),
impulse
0('_, 1
is
8ma × respectively
duration,
variables
[
l('_'6'n'Oma×)=°cc-2sinO(_'6'n)L 8(T.6.n)
and
pulse
satellite
N
where
zero
in
measured
at
At=tmax-6.
the
function
to
_,
e,
n,
can
and
now
@max,
be
i.e.
6,n)72
0--m_x
(6.4).
(6.4)
response
In
reduces
(6.6)
J the
to
limit
the
of
simple
large
satel-
form
l
O(_,O,n)=cos-l(1-_) and
(6.7)
(6.6)
becomes
2'(T,0,/'_,0max)
= 0ceNt/2(1
The quantity'e (6.4) can be point,
-_)[
1 -
is typically easily solved
cos-'(1-,)] Omax
2
small and, by iteration
(6.8)
for nonzero values using (6.7) as a
of e, starting
i.e. I-T (6.9)
[COS0(T'6'/_)]i÷I
= ]-6_
until
it
As
illustration,
an
response silica), value use
converges.
of L= 6 =
a
l-nzl--+[[c°se(x'E'n)]J]2--n
value
let
the LAGEOS 1.905 cm,
.093. 0ma
We x
=
us
(6.6)
satellite. and Rs =
recall .75
use
rad.
29.8
that,
to
Substituting cm into
for
Now,
estimate
solid
using
n = (6.5b),
cube
(6.6)
the
and
impulse 1.455 (fused we obtain a
corners, (6.9),
we we
can obtain
the plot of the LAGEOS impulse response shown in Figure 4(a). The profile shows the characteristic fast rise and long tail of the LAGEOS response. Furthermore, if we compute a center-of-mass correction from the centroid of this impulse response profile, we obtain a value of 250.2 mm which is in excellent agreement with the accepted 1977].
LAGEOS
value
of
249
±
1.7
mm
[Fitzmaurice
et
al,
The impulse response in the large satellite limit, given by (6.8), is shown in figure 4(b) for the case of solid quartz and hollow cubes. Note that both the temporal width of the reflected pulse and the target optical crossection is smaller for the hollow cubes than for the solid cubes because of their smaller field of view.
7-46
1.0
I
08
N_
I
I
I
I
I
_
06
0.4 0.2
L_
0
J 100
0
I
200
300
400
500
_d_-600
700
t (PICOSECONDS)
0.06
uJ o9 z O O..
o9
i
I
i
I
i
_OUAR_cuBE_ 0.04 0.03
W
nr" w o9 ....I
0.02 0.01
O..
--
0
i
I_l
0
I
0.1
0.2 Z=_
Figure puted large 7
4: (a) Impulse response by our simple analytical satellite limit for both
FEASIBILITY
OF
MILLIMETER
2R
of the model. hollow
ACCURACY
0.3
LAGEOS satellite as com(b) Impulse response in the and solid quartz cubes. SATELLITES
We will now demonstrate that, in order to achieve high optical cross-section simultaneously with minimal pulse spreading with a spherical satellite, we must increase the satellite diameter and/or retroreflector density and simultaneously restrict the response to retroreflectors within a relatively small solid angle on the satellite surface about the station line o5 sight. 7-47
The total time duration of the sity points) can be determined
At = --('_max=C which,
in
-R'0
the
_
t2sin
limit
of
--+62 small
maximum
Eq.
(5.4)
for
n2
incidence
0%
inten-
1 angles,
(7 .1) reduces
to
the
satellite
optical
cross-
N
O _,,,
(7.3)
As mentioned earlier, the angular recessing the retroreflectors in (7.2) into (7.3) yields OccN
response can their holders.
be restricted Substituting
CAtmax
24 We
to
(7.2)
same limit, reduces to
o'- -_-
0 =
1
COS Omax
(0% e.
e(l+
[-
In the section 0"co
E)
reflected pulse from (6.5), i.
by
(7.4)
R,[1-"_(I+_)]
can
now 8
express
the
total
number
of
retroreflectors
as
2
(7.5)
N=4p_ where sents faces. 0_
_ is a "packing density" ( = .435 for LAGEOS) which reprethe fraction of total surface area occupied by the cube Substituting (7.5) into (7.4) yields our final result [3R_cAt
(7.6)
6Ri The
product
_RscAt
that, if we wish some factor (via we must increase radius get 8
product
in
(7.6)
quantifies
our
earlier
statement
to reduce the amount of pulse-spreading At by reduction of the retroreflector field-of-view), the retroreflector packing density -satellite
(_Rs)
by
the
same
factor
to
retain
a
similar
tar-
cross-section.
CONCLUSION
As mentioned previously, the principal technical challenge in designing a millimeter accuracy satellite to support two color observations at high altitudes is to provide high optical crosssection simultaneously with minimal pulse spreading. Increasing the satellite diameter provides: (i) a larger surface area for additional cube mounting thereby leading to higher crosssections; and (2) makes the satellite surface a better match for
7-48
the incoming Simultaneously by recessing fraction of phasefront For
planar phasefront of the laser beam as in Figure 3. restricting the retroreflector field of view (e.g. it in its holder) limits the target response to the the satellite surface which best matches the optical thereby
near
term
reducing
experiments,
the the
amount small
of
pulse
radius
of
spreading. STARLETTE
makes
it
an attractive target for testing and.evaluating two color systems or for testing atmospheric models. Furthermore, its low altitude (960 Km) and moderate target cross section results in relatively high received signal levels. AJISAI, also in a relatively low 1375 Km orbit, consists of small clusters of retroreflectors separated by large reflecting panels and has comparable signal strength to STARLETTE. Unfortunately, the satellite is quite large and simultaneous returns from several retro clusters results in a complicated satellite signature [Prochazka et al, 1991]. seconds
From FWHM
although, individual certain
Figure 4, LAGEOS spreading is in agreement with [Fitzmaurice
in
excess et al,
of 150 1977]
pico-
with sufficiently short laser pulses ( co
0
0 L.O 0
_D
I
0
o O0
0 0 4.
I::::1
I
0 L._ o
C_ O0 I---
.,:-I CO
LLI .._1
o
!%0
8-14
!
N94-15587 GEOMETRIC
ANALYSIS
B.
OF
CONKLIN,
S.
Bendix
SATELLITE
BUCEY,
Field
LASER
V.
HUSSON,
Engineering
J.
The the
analysis
method
of
presented use
with
of
has
a
potential
In centimeters
_he
and was
community substantially.
Most
shot
data
has
single
During
shot the
satellite
positions
term
for
used
the of
on
that
trilateration analyzing
lower
other
The
major
the
station
determined
from to Our
or
steps
that
starts the
must
fullrate as
written
data the to
data
tape.
simultaneous pass
of
for
4 each
After data
the
more
pass. file. of
points
solution,
has
These
Poorly
The the
polynomials
are
created
fitted
although
for
this
are
rarely
8-15
not
allow
been
removed occurs.
for
can
be
is
also
data. data
The
observations
second
for
from
preprocessing process selects
during
a polynomial
30
need
Software
and
means
to
biases
that
analysis. tape.
have
passes
does
several
continues
at
the range
simultaneous
meteorological
process
as
determination
precision
polynomials, and
way
Trilateration
release
of a
radiation
method
are
found
a
orbit
low
have
The
provides
information
and
data
It
include
the
There
been
that
advantage
separating
other
stations
a
of
improved.
drag,
process.
the
with
determine
such
the
requires
statistics
all
polynomials.
corrupt
or
timeframe
output
that
fullrate
ranging
much
primary
in
in
ratio
prepare
to
orbit.
in
and
stations.
LAGEOS
polynomial an
fact
field
- 15
improved data
were
satellite
difficulty
the
has
and
trilateration
trilateration
to
produce
of
used
determination
ranging
which a
as
signal-to-noise
occur
Once
the and
orbit
now
quality
are to
gravity
a monthly in
timeframe.
such
an low
laser
with
passes
the
method
more
such that
10
ranging
laser
data
The
data
monthly
about
laser
analysis
independent and
was
the
trilateration. is
data,
data
methods
data
disadvantages
height, of
susceptible
is
with
centimeter.
mathematical
models
ranging
extraction
four
geometric
influences
methods.
the
the
outside gravity
from
1970s
1
the
Trilateration
studies
centimeters
below
is The
demonstrate
international
2
1992
positions.
satellite
stations
precision
to
using
to
millimeters.
of
below
positions
and
simultaneous
ranging
technique
pressure,
the
1987
station
laser of
time
using
station
of
investigated
provide.
- 12
precision
LAGEOS
method
and
deformation 3
precision
the
laser
precision
a
regional
that
and
is from
simulated
distribution
Since
expanded
data data
satellites
between
the
global
poor.
has
single
1970s
the
is
these
for
of
rates
data
solutions
Center
laser
baseline
Etalon
Project
Flight
Analysis
coverage
American
Dynamics Space
simultaneous
selected
global
great
LAGEOS
stations
of
simultaneous
additional
DEGNAN
Goddard
trilateration.
DECKER
MD
901/Crustial
NASA
W.
DATA
Corporation
Seabrook,
Code
RANGING
is
the
fit
other
to
information
information, through
same
the
the
are entire
determined, intervals so Any
that time
from
the
they
don't
intervals
within A
the
selected
summary
produced
at
of
this
separated
into
Commonwealth Americas,
of Easter
To
station
velocities
to is
step.
is
the
the data. started.
position position.
with
and
edits.
A
epochs. 4
P
the
is
the
repeated
than
of
the
This
database
observations
in
for
a
solution
by
and
Figure
contains the
European
2.
point
linear
weighting
the
month.
term
solutions.
The
high
stations
of at
rates
are
of
each
of
rates
of
trilateration
this
method are
requirement
for
satellites. high time.
The altitude However,
lends
8-16
of
data
offer to
one
which
a
satellites
month of
is
shown
and is
a
computed
observations
which
satellites Etalon
a
in
during
Figures
to
doing
3-5.
long
stationposition
method
ranging
the
for
by-product
itself
area,
visibility
simultaneous
for
database.
baselines
of
and
of
illustrated
over
Etalon
x,y,z
a
the
number
simultaneous
and
The
combinations
initial
a broad
is
in
of
from
This
are
determined
sample
station
the
determined.
coverage
a
are
O-Cs process
both
A
are
iterations
are
1.
and
analysis
from in
have
is
4
still
stations
turn
great
larger
to
the
reached.
summary
plot,
the
these
number
Figure
also
both
satellite
saved
in
the
with
corrections
for
sample
generated
baseline
In
one
shown
baseline
method
their
is
These
lengths
the
A
sample
geographic
altitude
because
and
distribution
fit
the station velocities under development.
requires
month
stations.
respect
consecutive
and
inverted,
with
average
been
the
times
by
determined
solution
monthly
Some
The
is
of 12
then
O-Cs
iterative
have
baseline
all
(ie.
Again
between
by
multiplied of
This
O-Cs
The
the two
set
iterations
the
then
along of
elements
for
and
the
determined.
position
solution
Baseline
that
six
in
also
new
done
vector
coordinate
of
summary
file
number
is
O-Cs
computed.
a
the
height.
between
least-squares
then
and
of
station
the
is
A
the
generated
are
reiterated.
or
involved
is
O-Cs
O-Cs
percent,
stations
The
and rms
the
is
new
delta
longitude
only
the
the
each
derivatives
a matrix
and
for
P matrix
positions
P matrix
one
change
latitude,
period
the
until
less
and
computed
by
performed
partial
and
the
average editing
summary
This on
applied process
an
6-sigma
position
has
each
and
with
run
station
station
for
the
iterative from each
a
and
at
recomputed.
the
generated.
the offset
transpose of
station
are
multiplied
then of
position.
partials to
positions
total
P
matrix
per
LAGEOS
positions
computed
along
is to
of
position
using
position
the
determined
epoch
is
Africa,
for
station
are
edited
written
each
is
station
resulting
is
A
the
adjusted
applied
effect
procedure
stations).
where
is
each
is
corrected an values (O-Cs)
each
then
observations
to
what
for
are
matrix
offsets
This
rms
of
sensitivity small
has been computed
data
North
section
is
deleted.
also
tracking
stations
corrections
satellite
and
number
determining
for
average mean
each
position
is
Europe,
Apriori each
are
yield
section
satellite
are
for
other
dependent
O-Cs
stations
LAGEOS
is
The
compute
determined
The
the
total
applying and
are
stations
the
to
4 data
remaining
section
software.
Once all the data The observed minus
satelllte each
used
angle
than and
geometrically, the
The
that
satellite
of
the
States. Huahine.
and
by
are
fewer
stations
One
data
in
month.
so
criterion
the
read
have
Finally,
sections.
analyze
observation
that
available
Independent Island,
data
of
the
two
ranging
middle
passes
output
requires potential
number had
of a
low
global
ranging
stations during be
at May
used
priority any
and
for
data launch
3
simultaneous
about
65
period
from of
a
velocities. expected biases
the
the
include individual
on
the
we
will
these
4
and
In
that
accurately
and
the
8-17
and 2,
at
an
only
1
scheduled
to
obtain
for a
inclination
obtain
of
simultaneous
satellite.
geometric
Etalon
analysis
2,
spread
baselines
and
geometric
determination
sets.
the'campaign
addition,
SLR
can
analysis.
opportunity
determine to
satellites
stations
to
two
performed
data
simultaneous
Etalonl
than
was
LAGEOS
best
priority
expect
additional data
from
opportunity
a high
modifications the
next
an
more
priorities,
sets
set.
be
LAGEOS2,
well
geometric
simultaneously.
data will
Etalon
by
campaign
how and
data
offers
future,
days,
low
ranged
Etalon
determine
ranged
sets
rarely
research
ranging
LAGEOS, few
to
ranging
there
Future to
from
of
1992,
data
In data
1992
station
degrees,
trans-atlantic
of
of
are intense
Dynamics
October
large
they An
simultaneous
where
in
June
because
no set
so
time.
Crustal
Unfortunately, yielded
one
analysis of
range
over
software and
time
a
are
II
II
tl
II
II
II
II
II
@@
UUUUUUUU
8-18
Z
0._
x
MXXUxX
xI xu I
(.0 0 [.J
xxx
.,-I
'_
(]Z
xxxu
GO GO
mini
[J
Nx Wx Uw Xw XN Xw Xx x M
f
UXMW XN
I
IXXxzxxx
I
_z xz
•
-:r t._ CO
C_
O) _r q
"*
% *-'4
"_
o
8-19
• /\
x
Lt_
8
Lt_
Q Lt_
II
a--
"'Z r.1
X \ #
i
X X X
x >< 0
0
X X X 0
0
0
0
0
0
d
0
CWW)
8-20
3NIq_S_8
"(._
n_
"'Z
I • t
| II
B
0
.
° 0
0
0 UI
(NNI 8-21
_NI_SUg
8-22
8 th International Session:
Workshop
Mobile
on SLR Instrumentation
System
Upgrades
/ Developments
N94-15588
IMPROVEMENT M. KASSER,
OF SLR ACCURACY,
ESGT,
18 All6e
J. Rostand,
A POSSIBLE BP 77,
NEW
91 002
STEP
EVRY
France
Abstract
s .....
The SLR technology experienced I..... i,, 1970 les, leading now
Presently it apl_ears as the atmospheric
as useless propagation
proposed since many years considerable technological delayed
such
a large number to a millimetric
to increase these delay suffers
of technical improvements instrumental accuracy.
instrumental performances as long its actual imprecision. It has been
to work in multiwavelength difficulties of subptcosecond
mode. but up to now the timing have seriously
an approach.
Then a new possibility is proposed, using a device which is not optimized now for SLR but has already given good results in the lower troposphere for wind measurement: the association of a radar mad a sodar. While waiting for the 2-k methodology, this one could provide an atmospheric propagation delay at the millimetre level during a few years with only little technological investment.
I/ INTRODUCTION It has been pointed out since a long time that all space geodesy techniques have to deal with the same general problem, i. e. the crossing of the atmosphere reach either an artificial satellite, or the moon, or a star, or a quasar, etc... Nevertheless,
if it is the
same
atmosphere
known to be quite different for radiowave ones suffering more than the other ones is corrected classically by two-frequencies transit (because of the atmospheric
for every
techniques,
the
effect
to
is
and for optical methodologies, the first from the crossing of ionosphere (but this methods) and from the troposphere water vapor content which is quite
unpredictable and has a strong impact on propagation of radio waves optical ones). Considering these aspects, the general advantages of radio compared with optical ones in geodesy are their aU-weather capabilities, drawbacks are linked with their poor tropospheric correction quality.
and not on techniques and their
As long as the instrumental accuracies were at a few centimeters level, this meteorological aspects were of secondary concern. This is no longer the case since many years with VLBI, who had to use costly water vapor radiometers to upgrade the tropospheric correction to an excellent level (and since this period, VLBI has got the best positioning precision among all space geodesy techniques). Since a few years
too
it is no
longer
the
case
with
satellite
8-23
laser
ranging,
which
is able
of an
internal instrumental positioning accuracy only problems SLR stations),
precision of a few millimeters, to be compared with the final ! of 2-3 cm. Of course the tropospheric corrections are not the
biasing the results (consider but significant improvements
for example the poor world coverage of of this parameter must be researched.
Many teams have pointed out that multiwavelength methodology required amelioration. Anyway it is quite clear that this will ask
could p_vlde this for a tremendous
technological effort and will probably not be operational since some years. For that reason we have looked for a new solution, able to give better tropospheric correction with up-to-date' techniques, even if probably not as efficient as 2-colour method, but immediately available.
II/THE
and
ATMOSPHERIC
CORRECTION
If n is the Index of refraction, c in the atmosphere). Classically
we define
and
for optical
wavelengths,
N=A_(P.
/T).{
SLR
n = c o / c (c o is the light
the co-index N=
FOR
(nusing
of refraction 1).10
celerity
In vacuum
as
6
for example
Essen's
I ÷ (a-b.t).P.}-B
x(Pv
formula: /T)
where P. is the atmospheric pressure, Pv is the water vapor pressure. T is the absolute temperature and t is the centigrade temperature. Ax and B x are _.dependant parameters, and a and b are constants. With a I0 -7 precision it is acceptable to use the simplified formulation: N=A'_tP.
/T)-B_(p_
/ T)
We define also the geometric length of the optical ray Lg, the optical path Lo, and the geometric distance L between two points s o and s t being one at the ground level and the other beyond the atmosphere, at the satellite level:
$1
$1
,, = fa,
L. = f,(,).d,
so
the
so
If we call AL = L o - L. it is a function of tile angle direction of the satellite. We notice that: AL= L ± _2± i:
:
tL o-Lg)
a between
the
vertical
and
+ (L z-L)
::
As the Curvature
of the ray pa{i_ ]glow.
and
as this
curvature
only on a small range (a few tens of kilometersL the difference considered as negligible. On another hand. AL can be expressed AL = f(a) . AL,,_tl_ t
8-24
IS experienced
Lg - L IS generally as:
And the function f(a) may be found in (Berrada-Baby et al., 1987 or Akhundov et Stoskii, 1992). We have now to deal with AL for _ = 0. h o being the elevation of the SLR station above "sea level",
w
AL = f N(h).dh ko
for these
Considering the very optical wavelengths,
low dependance we will focus
of the result regarding on the "dry" part of this
the water expression
vapor AI d :
m
AL,: f A P--'.dh T ho
And. p(h) being atmospheric pressure h. with R = 287 J.kg/°K
the and
* P. = p(h). * d P(h)
air density. T(h) the absolute temperature, g(h) the acceleration of the pesanteur at the
R.
P(h) the elevation
T(h)
= p(h).
g(h).
dh
so that.
AL d = f
dP(h).A.R
ho g(h)
At this
level
we may
have
different
assumptions:
I 't hyp.
g(h)
= go = constant.
2"
g(h)
- go / ( 1 + 2.h/r
hyp.
aLd-
And
gradient
the difference
AId = A'R'Po
o ) closer
to the
/ go reality.
We find
then:
A.R.P o I
+
ro -p- (go ÷ R. "to
8o
( _ is the
Then
of T ). For Po = I000 between
these
mbar,
two models
- 2.go
we find is below
]
ALd -_ 2,3 I cm
meters
: various
studies
show (Berrada-Baby. 1987) that this discrepancy is around 5 mm. and is quite stable and thus easy to model. On another hand, the differences between the second model and real data deduced from (Cira 1965) campaigns are quite small (I mm
typically).
8-25
So excellent And one
we conclude that it is extremely important to measure I% with an precision (1 mbar of error induces 2.3 mm on the atmospheric correction). must take into account the fact that the function f(a) (that is the air-mass
number) will measurements.
multiply
these
If the temperature is fig. 2, we observe that half the upper layers are quite compare these facts with around 1-2 mm, multiplied it is clear will leave
values
by
numbers
up
to 2.5
in operationnal
SLR
measured in the first 5 kilometers, looking at fig. 1 and the total correction is already acquired (fig. I), and that well defined by the profile in the troposphere. If we the abovementionned value of 5 mm. whose noise is by the air-mass value (I to 2.5), i. e. less than 5 mm,,
that any temperature profile of good a residual error on the atmospheric
precision correction
acquired at the
in the troposphere millimeter level.
1.0C ff Jf
3.gc
J
3.8C
J /
).7C 3.6C 3.50 /
3.40 ).30 ).20 3'.10 ).00 0
10000 5000
20000 15000
30000 25000
Fig. I: Fraction (Y-axls) of the total atmospheric correction for a vertical transit of a laser pulse, from the ground level up to a given altitude (X-axis, in meters). Computed from an observed radio-profile in Greece, 1990.
8-26
Z[_a! J
\
_\
6C
/ /
/
I I I
/ 1963
temperature Avenge standard
20 ¸ II
II
_emperat'ure 1961
1963
BCA-60
!
i I
\
0
2o0
15o -150
-]00
250 -50
3or, 0
T[CK ] 40
T[ c
'
Fig. 2: Typical temperature profiles (from CIRA 1965)• If the possible variations are quite large, it is also noticeable that the profiles have the same topological aspects and are quite "parallel", with no intersection from one to another.
8-27
HI/PROPOSITIONS The first one is obviously to measure Po quite carefully. calibrate often the barometers employed, to measure preferably to the level of the axes intersection of the telescope (it is generally
It is necessary to the pressure close the case). It must
be posslble
< 0.2
to measure
the pressure
with
an absolute
precision
mbar.
Considering the efficiency ofbarometric levelling, whose precision may reacll one meter, we observe that it means that constant pressure surfaces are quite horizontal, so that it is useless to measure the horizontal gradient of Po in order to correct its effect in the direction of the sight, provided the weather is reasonably quiet. Anyway, it seems mostly advisable to improve the correction by a good measurement of T(h) in the direction of the satellite, at the O. I°C level, up to an elevation' of 3 to 10 km. In these
conditions,
one
may
be sure
to get
an atmospheric
than 1 mm. It is easy to notice that such a precision require a 20 times better precision on the differential between the two colors (i. e. 0.5 picosecond), which
correction
better
with 2-wavelength SLR will time-of-flight measurement is quite uneasy to reach.
The solution we propose for an easy measurement of the temperature profile along the llne of sight is a SODAR (Acoustic LIDAR) associated with a RADAR, the acoustic and the radio wave having the same wavelength. The radar is used to track the acoustic wave, so it allows to measure the speed of the sound in the atmosphere, which in turn provides an excellent temperature profile (at the 0. I °C level). Such instruments (e. g. Remtech) are now used close to airports, in order to measure winds and wind shears, and this technology is already available. The common
ranges
are
3 to 5 km,
but
large
8-28
instruments
may
reach
I0 km.
IV/
close that
CONCLUSIONS We propose that an experiment be carried with a radar/sodar equipment to an up-to-date SLR station in order to check the possible improvements such data could provide to the laser data. This solution is probably an
excellent stations.
alternative
allowing
to wait
for
On barometric
another hand. we insist on the equipments used in SLR stations,
important
to perform
a good
atmospheric
the
2-wavelength
necessity as the
generation
to check P, parameter
of SLR
quite carefully is by far the
the most
correction.
BIBLIOGRAPHY
H. BERRADA-BABY.
P. GOLE
& J. LAVERGNAT
Effets de la troposphere sur les mesures de distance Terre-Satelllte. Application au proJet DORIS. CRPE/158 Technical note. June 1987 RPE/ETP, 38-40 rue du G6ndral LECLERC. 92 131 ISSY-LES-MOULINEAUX, France
CIRA
1965
North-Holland
T. A. AKHUNDOV,
Publishing
Company.
Amsterdam
Edition,
1965
A. A. STOTSKII
Zenith angle dependance of path length through the troposphere Proceedings of the symposium "Refraction of transatmospheric Den Haag, 19-22 May 1992, pp 37-41
signals
REMTECH Company, technical papers on acoustic wind profilers. Remtech Inc., 1,040 Townley Circle, Long_ont, CO 80 50 I, USA
8-29
in geodesy".
Operational
Software
Developments
N94-15589 On the Accuracy
8th International
of ERS-1
Workshop
Orbit
Predictions
presented at on Laser Ranging
Annapolis, May
MD
18-22,
Instrumentation
USA 1992
by R. Kt_nig, H. Li, F.-H. Massmann, J.C. Raimondo, Deutsches Geodiitisches Forschungsinstitut, German
Processing
C. Rajasenan, Abt.I (DGFI)
and Archiving Facility MiJnchner Str. 20
D-8031
Ch. Reigber and
(D-PAl)
Oberpfaffenhofen Germany
Summary Since
the launch
cessing
and
of ERS-1
Archiving
(first European
Facility)
provides
Remote
Sensing
regularly
orbit
predictions
The weekly The tuning
distributed procedure,
(Satellite Laser Ranging) tracking network. called tuned IRVs and tuned SAO-elements.
Satellite)
the D-PAF for
the
(German worldwide
orbital elements are designed to improve
accuracy of the recovery of the orbit at the stations, is discussed based on numerical This shows that tuning of elements is essential for ERS-1 with the currently applied
ProSLR sothe
results. tracking
procedures. The the bias
orbital time
piled and
bias
function
Finally
elements
the for
are updated
function increases
quality
about
250
has considerably
by daily
distributed
is explained.
Problems
the prediction
accuracy
assessment days
since
of ERS-1 launch.
and
bias
numerical
functions.
results
The generation
are presented.
The
of time
considerably.
orbit The
iime
predictions
average
improved.
9-1
is described.
accuracy
lies
in the
The
accuracy
range
is com-
of 50-100
ms
1. Background Since
and
the very
Introduction
first days
when
ERS-1
predictions to the SLR community. tablished IRVs and SAO-elements. elements are very compressed the orbit. The trick to achieve luminated Very
from
soon
the numerical
after
launch
forms of complicated this is called tuning
The
it became
clear
extremly such
high
solar
the D-PAF
is sending
orbit
in form of the well es2. Though these orbital
orbit trajectories, they of elements. In chapter
that the ERS-1
orbit predictions the time bias
Meanwhile the time bias function features of the time bias function
events
in space,
optimally represent 3 the problem is il-
point of view.
and geomagnetic activities. The The D-PAF therefore introduced daily. Some
began his mission
The orbit predictions are produced The procedure is given in chapter
activity
as a geomagnetic
is extremely
affected
has become an accepted tool in the SLR and related topics are explained in chapter
in the
storm
trajectory
first
of nearly
by solar
lost accuracy mainly in along-track direction. function which is generated and disseminated
months
of
singular
the
type.
mission
Though
brought
SLR
community. 4. extraordinary
tracking
was
almost
lost for two days, the D-PAF orbit prediction system (and the SLR community in turn) gained at the end. The software system got more backup solutions and the quality checks were largely extended.
Chapter
Finally the orbit becomes obvious the more
prediction from the
detailed
2. Generation In a first
analysis
of Orbit
step
DOGS-OC
5 tells more
the
system course
quality
assessment
has developed of the average
in chapter
and quality
checks.
to a reliable system in SLR tracking. This. accuracy of the orbit predictions shown in
5.
Predictions
orbital
(DGFI
about
Orbit
parameters and
are estimated
Geodetic
parameter
by differential estimation
orbit
System
correction
- Orbit
with
the
Computation)
software. Laser ranges are mainly used as observations for the least squares procedure few cases also RA FD data (Radar Altimeter Fast Delivery) ( Massmann, F.-H. et.al.,
and in 1992 ).
The use launch.
prior
Orbit
of PRARE
data
perturbation
represented by non-gravitational OC adopts!a Earth's high activity
models
(Precise
used
the GRIM4-S2 perturbations
Range
are
And
state
gravity of the
Range
of the
rate Equipment)
art ones.
field model low altitude
The
( Schwintzer, orbit stemm
was
also planned
gravitational
forces
are mainly
P. et.al., 1992 ). The major from surface forces. DOGS-
macro modell of the surface of ERS-1 for albedo, direct solar radiation and drag. atmosphere is represented by the CIRA'86 model where solar and geomagnetic
is needed
as input.
In a second ters derived
step the orbit is integrated forward by the DOGS-OC software with the paramebefore. Adopted are the same perturbation models but now solar and geomagnetic
activity
predicted
that
are
degrades
to
for the respectiv
the accuracy
of ERS-1
time period. orbit
predictions.
And
this indeed
Also
the ERPs
ters) are predicted for the time period of the forward integration. tions is quite good for the lifetime of ERS-1 orbit predictions, neglected. 9-2
is the major (Earth
error
rotation
source parame-
The accuracy of ERP predicthe effect can therefore be
In the third step DOGS-PD (PD for Predictions) compresses the orbit to dedicated forms and formats of orbital elements which can easily be disseminated worldwide via various telecommunication channels. In addition these elements are tuned so that the user will recover the orbit in an optimal (Smithsonian elements
way.
So-called
Astrophysical
to the PRARE
tuned
IRVs
Observatory)
(Inter-Range
are
Vectors)
delivered
to
the
and
tuned
SLR
SAO-elements
community,
PRARE-
system.
3. Tuning The orbit
is recovered
computers.
These
nongravitational starts cover
at the SLR
programs forces
sites by simple
adopt
as drag.
low The
degree
and
IRVINT
of these
despite
severe
of simple
optimum
neglections,
perturbation
is a minimum
program
D-PAF
modelling
difference
tunes
onsite
IRVs
squares
orbit. The IRVINT assumes for IRVINT
GEM10N
up
gravity
should run coefficients.
field
in the
RGO
coefficients version
to degree
(Royal
Fig. 1 shows the along-track error if an un-tuned holds in general. Due to the missing drag forces ca. 1400m ;in along-track the satellite.
position
and
Greenwich
or ca. 200ms
gravity
fields at the
and
and
do
orbit
SAO-elements.
consider of Texas
theory
18. The
orbit
to re-
means
that
way.
The
in an optimal
and AIMLASER a 60s integration
Obse_atory)
not
This
of the recovered
order
capacity
university
analytical
is recovered
sense
perturbation model orbit or reference run then in a defined mode. D-PAF
for use on low
written applies
the orbit
in the least
intended
order
integrator
from the IRVs. The ancient AIMLASER the orbit from the SAO-elements.
Because
programs
to the full
programs step size
have to and the
AIMLASER
program
dedicated
GEM10B.
with
IRV is integrated by IRVINT. The example modelling the error grows during the day to in time
bias
which
would
prevent
tracking
of
Fig. 2 displays the error after tuning. Maxima are now ca. 20ms around midnight and around noon. The remaining along-track errors are similar day by day, the maxima are dependent on the
solar
a day.
The
remaining
activity. more errors
They
could
proper
way
are in a range
be accounted of course
for by a function
would
be to model
that can be accepted
9-3
giving
drag
for tracking.
the error
in the integrator.
for 24 hours Anyway
of the
[ m ]
ALONG-TRACK ERROR
1200
1oo0
800
6O0
400
200
DGFI 2
4
6
Figure
8
10
12
1 Along-track
"
'14
"
1.8
1.8
20
error from un-tuned IRVs
ALONG-TRACK ERROR
[m]
[h]
22
J
150
1oo
5O
-5O
-DGFI -lO0 o
2'
4
6
8
I0
12
Figure 2 Along-track
9-4
14
1"6
18
error from tuned IRVs
20
2"2
[h]
The accuracy
of tuning,
that is the difference
of the recovered
orbit to the reference
orbit, can
be seen in Table I where the typical differences are given as RMS-values in meters for both types of prediction elements. Again the values are largely dependent on the solar activity.
Table
IRYs
SAO-elements
ld
lOd
radial
3-5
10-20
across-track
3
10
along-track
20-60
20-100
1: Tuning
The
accuracy
SAO-elements
(in m)
show
less
accurate
recovery
period (normally 10d) whereas the IRVs
because
they
represent
the whole
prediction
are given each day. All values are within a range
thatcan be accepted for tracking. 4
4. Time
Bias
D-PAF Due
generates
to the
curacy
and disseminates
sensitivity
mainly
bias provides Therefore Look)
D-PAF
prediction
to variations
direction.
and simple
generates
ranges.
relative
and
For every to the
update
pass
IRVs
is also rises
known
the predictions
to the
too early.
stations
The
function.
over
A typical
example
removing
the outliers
The time
bias
of time
function
is capable
of predicting
The
(European
EDC
problem. Currently in real-time
The function
bias
daily a time all stations
set.
A third
fits to the time
values
bias function
having order
Data
Center)
available
to other
values
from
observed function
bias values
in Fig.3. check
the time bias
the along-track
actime
of the time
Fig.4
new
ERS-1, in time
Q/L
a time is fitted
(Quick bias
is
by LS
the time bias values are ,leading all in all to a best within
shows
1ms
for up to four
the fitted
function
after
of the parameters. of the last few days.
More
important
it
error. provides
Stations can store the observed Graz, Potsdam, RGO, Santiago
own computations to more confidence
is given
and after the significance represents
loose
as so-called
determination
(Least Squares) to these time bias values. In the LS procedure checked for outliers and the parameters are checked for significance approximating days.
and SAO-elements.
of the orbit predictions.
disseminates
last prediction
sets containing
of the high atmosphere
This
rises too late or the satellite
a quick
Laser
computed
of ERS-1
in along-track
bias i.e. the satellite
weekly
stations.
another
important
time bias immediately de Cuba and WettzeU The
stations
can
and with the D-PAF time bias function. in the time bias that is going to be used
9-5
then
tool
to handle
the
time
bias
after the pass in the data base. do so. This time bias is nearly compare
the
results
This all this together for the next upcoming
with should pass.
their yield
Time Bias
[ms] .0
-5O
-100
-150
DGFI 0.0
0,5
1.0
1.5
Figure
2.0
3 Time
2.5
3.0
3.5
4.o[_]
bias values
Time Bias
[ms]
-50
-IOO
-150
-200
0.0
0.5
1.0
1.5
Figure
2.0
4 Time bias
9-6
2.5
function
3.0
3.5
4.0[ d]
5. Quality The quality of the ERS-1 prediction products is indicated to the users by a quality flag. In case of orbit predictions the quality flag is computed from the fit of observations in the orbit analysis (step 1 in chapter 2), from the comparison of overlapping arcs and from the tuning accuracy. The quality of the time bias function is assessed from the approximation error of the function and the dam coverage. Of course the quality flag gives only an idea on how the quality of the products can be. By nature predictions go into the future and nobody can determine what will be. Particularly the accuracy of ERS-1 orbit predictions is heavily influenced by unpredictable solar activity. Anyway the quality flag shows the current knowledge of the quality. It convinces the generator that he did a good job and it gives a first indication to the user in case he has problems. All prediction products are subject to permanent quality checks. Dally the time bias of newly incoming Q/L Laser passes are determined relative to the actual prediction orbit which leads to the time bias function. The prediction orbit is also compared to the MMCC orbit (Mission and Management Control Center). The MMCC orbit is generated by an independent group in ESOC (European Space Operation Center), Darmstadt, from S-band observations and radar altimeter fast delivery ranges. The comparison with such a completely external source provides more confidence in the results. On a weekly basis when new orbit predictions are generated the new prediction orbit is compared to the old one. The differences in along-track direction should exactly reflect the old time bias function. The differences in radial and across-track direction normally stay within a few meters. The internal quality checks proceed in a closed loop from prediction set to prediction set. The external checks give an independent judgement. So the reliability of the orbit prediction system has reached a quite high level. Fig.5 displays the along-track errors of ERS-1 orbit predictions since launch. The first 100d are clearly affected by large solar activities. In addition a manoeuvre was missed. Meanwhile these cases are taken care of. In the right half of Fig.5 it can be seen that the mean accuracy steadily improves, but is clearly degraded by the frequent manoeuvres.
9-7
[ms]
Along-track
Errors
(7 days
moving
!t!
4OO
mean)
i!
i !i! i!
",i n°'uvi
so,or _u_i
•
! i!i!i ! i !i! ! i!i!i i, ii! i! ! •
ii!
i
.3OO
i'
i •
i
200
°
i DOFI
°
i !i!
i!
i !i!
i!
i
i !i!
i!
i
,!;i
;!
i_
i!
.
ii!
_i
iii
iil
! i!i!i
100
ii
0
i
i •
50
0
100
Figure
°
150
5 Accuracy
of ERS-1
.
200
orbit
[d]
250
predictions
6. Conclusions It has been ly time
bias
shown
that
functions
ERS-1 prediction manently checked since launch.
tuning
of orbit predictions
that account
products internally
is essential
for the along-track
for ERS-1.
D-PAF
error of the predictions.
provides The
is assessed and indicated to the users. The predictions and externally. The average accuracy has considerably
dai-
quality
of
are perimproved
7. Literature Massmann, Laser
F.-H.,
Reigber,
Ranging
Ch., Li, H., Ktinig,
Network
Performance
R., Raimondo, and
Routine
J.C.,
Orbit
Rajasenan,
Determination
C. and M. Vei: at D-PAF,
this
proceedings Schwintzer,
P., et.
sungswesen
14 al.:
GRIM4
117, pp. 227-247,
- Globale 1992
9-8
Erdschwerefeldmodelle,
Zeitschrift
£dr Vermes-
N94-15590
COMPENSATION FOR PRED%CTIONS
THE DUE
DISTORTION TO VARYING
Matti Finnish
IN SATELLITE PULSE TRAVEL
LASER TIMES
RANGE
Paunonen
Geodetic Ilmalankatu
SF-00240 Helsinki, Telefax:358-0-264995
Institute IA Finland
ABSTRACT A method for compensating for the effect of the varying travel time of a transmitted laser pulse to a satellite is described. The "observed minus predicted" range differences then appear to be linear, which makes data screening or use in range gating more effective.
I.
INTRODUCTION
Accurate range predictions are necessary in satellite laser range measurements when the operation takes place in daylight. Then the range gate, where the return pulse detector is active, can be set very narrow to effectively discriminate against noise. Data screening of the observations is often done using ',observed minus predicted" (O-C) range differences. The predicted satellite times are generally equally spaced, as are the transmit times. But the true hitting times are not equally spaced because of the varying pulse travel times. This leads to distortion of the O-C differences which can be as high as 10-20 m. A polynomial of suitable degree is used in screening. It is well known that the polynomial should be of low degree so as to avoid an artificially good fit or end effects. If the travel time distortion is removed, the O-C deviations are nearly constant with time for high quality orbit predictions. This paper describes and tests a simple correction method.
9-9
2.
METHOD
The
OF
range
RANGE
from
CORRECTION
the
laser
station
to
the
satellite
varies
approximately parabolically with time, Fig. i. When the satellite is passing the closest point, a small time change does not affect the range much. At the far end of the pass the range changes several kilometers per second.
\
P /
\ \
%
\
A Ri/_'
TRUE POSITION
Rmin
Ri_/
Ri
o
CALCULATED ....
/ _/
Fig.l
LASER STATION
Conceptual scheme for the time distortion in ranges.
origin
ot
the
travel
This rate , vi , can be calculated together with ranges, or it can be approximated from the change the successive predicted ranges Ri_ ] and R i vi = where The
T
is
travel
Rmi n
, and
the
time
step
rection
c
difference
the
instantaneous
is
the
_R i to
speed be AR
Ri_] ) / T
(often
time
Zit i = where
( Ri -
between range
the
Minimum
_
is
light.
Then
to
the
predicted
i = vi
*
At i
•
range
(2)
,
added
9-10
(1)
,
1 s).
(R i - Rmi n ) / c of
the between
the
travel range
time
cor-
is
(3)
3.
RESULTS
AND
A test involved
with
program /i/. A
used 220 ms
DISCUSSION
real data relatively
is few
shown in Fig. observations
highly accurate time correction
long-term was used
12 EIO
o
"_°.o. 8
o
a)
\
o
@
°
6
,.ul
o o
,,,
4
"_
2
IRV predictions the calculation.
-o. o
F--
_
in
METSAHOVI 1990-12-4 LAGEOS O-C DEVIATIONS
_..
z
2. This LAGEOS pass (21). The prediction
o\
,_
KEPLER-ORBIT 0
_
0 !
I
|
I
|
I
I
0
2
4
6
8
10
12
TIME(min)
z o
_-
8
o
6
>
'-'
METS_HOVI 1990-12-4 LAGEOS TRAVEL-TIME CORRECTED O-C DEVIATIONS
b)
E
I
16
FROM 15h57mo0 s
lO v
i
14
°o °'-°°°
--o __._°o o-
4
o
0 !
OO
(D
LI-NORM
0
I
I
i
I
I
I
I
I
2
4
6
8
lO
12
14
16
TIME(min)
Fig.
2.
FROM 15h57mo0 s
a) 'Observed-predicted' measured LAGEOS pass. b) O-C linear
FIT
deviations median fit
A
(O-C) Kepler
after the is shown.
9-11
deviations orbit fit travel
time
of a is also correction.
shown. A
The time error varies slowly known from earlier observations.
with
time, and is normally The O-C deviations are
shown in Fig. 2a. A simple Kepler orbit vations quite well, and only one outlier In polynomial fitting determination of easy. The first point would be rejected
/2/ is the in
fits the obserindicated. order is not a linear fit.
The situation becomes considerably clearer after application of the travel time correction method described (Fig.2b). The fit using the linear Ll-norm /3/ eliminated the last point as well as the known outlier. Because the model is now linear, it is not necessary to use higher order polynomials. This example possible in to 7.5 m of implementing As has been
shows that a very narrow range window is ranging to LAGEOS. A 50 ns window corresponds range. This would help considerably in daylight satellite laser range-finding. seen, the method can also help resolve difficult
data are
screening essential
tasks. Good orbit for this method.
elements
and
Note the O-C
that recalculation of the orbit after satellite hit times, produces approximately deviations as the method described.
the
a
good
orbit
pass, using the same
REFERENCES
.
The
Texas
University,
long
term
IRV-
predictions
for
LAGEOS satellite; a satellite prediction program developed at the Royal Greenwich Observatory, Herstmonceaux, England. .
.
J_ Kakkuri, O. of the Finnish Reports of the Helsinki 1978,
Ojanen, satellite Finnish ii p.
M. Paunonen, Use range observations cosmos Symposium Observations 1989, Cracow, of Artificial Polish Academy
ORBIT
M.
Paunonen, Ranging precision laser range finder. Geodetic Institute 78:8,
of
the Ll-norm to satellites. on the Use of
in
screening laser Proc. 18th InterArtificial Satellite
for Geodesy and Geophysics, June Poland (Ed. WI. Goral, Observations satellites of of Sciences,
9-12
12-17,
the Earth, No 27, 1989, Warsaw 1990),pp.359-362.
94-15591 Timebias
corrections Roger
Wood
and
to Philip
predictions Gibbs
Satellite Laser IL_nger Group Herstmonceux Castle, Ha_lsham East Sussex, BN27 IILP, UK
Abstract This talk aims to highlight the importance to an SLR observer of an accurate knowledge of the timebias "corrections to predicted orbits, especially for low satellites. Sources of timebias values and the optimum strategy for extrapolation are discussed from the viewpoint of the observer wishing to maximise the chances of getting returns from the next pass. What is said may be seen as a commercial data centres for
encouraging wider mutually beneficial
and speedier use of existing exchange of timebias data.
Introduction The real behaviour of low satellites is never in exact agreement The principal reasons axe that modelling the effect of atmospheric
with even the best predictions. drag is difficult, and the pertur-
bations due to solar radiation pressure are not predictable in advance. EI'tS-1 is much larger and somewhat lower than either Staxlctte or Ajisai and consequently presents the biggest headaches in making_predictions. Dcspitc the problcms, dctailed elscwhcre in these proceedings, the prediction teams do an excellent job in providing orbits and thereby chance of tracking the satellites succcssfully. Fortunately, orbit appears as an along-track crror and can be corrected predictions (as has been done 'very successfully for Lageos set of predictions observing stations can, for each satellite,
give observing stations the best possible most of the deviation from the predicted by applying a suitable timebias to the for many years now). For a particular model the history of the behaviour of
the timebias with time and extrapolate to predict the timebias at the time of observation of the next pass. At Herstmonceux we have been working to improve the accuracy of our extrapolation of timebias values. This talk outlines our findings, indicates the benefits to be gained from increased use of the data centres and shows how helpful good timebiases can be if you have English weather and are trying to keep us with Grasse! Why
do
we
We see three
need distinct
accurate
timebiases?
advantages:
Ease of satellite acquisition. This is always important, at whatever stage of the pass the satellite is first acquired. But it is especially important at the very beginning of a pass, necessarily at low elevation_ whcn accurate pointing helps to minimise the time spent returns. Ease of acquisition is also importaz_t when there has been a break
in searching for of a few days in
the scquencc of observations, because of cloud or technical downtime, where accurate knowledge of the timebias correction can lead to immediate recovery of the satellite. This second point emphasises the usefullness of having access to continuous records of timebias data in order to base any extrapolation on the best available data set.
9-13
Improved
telescope
tracking.
If an incorrect
timebias
is used
to compute
the telescope
position during a pass, the offsets from the reference time and the observer will have to insert ever-changing
position on the detector will depend on manual corrections in order to keep the
satellite
i_ [|ttle
image.
pointing Better
By contrast
a correct
model for the telescope noise
elimination.
timebias
results
or no guiding,
provided
that the
is weU-determined.
When
the timebias
is exactly
right the returns
from the satellite
always appear at the same place in the range window. This means that the window can be made very small and so the amount of noise reaching the detector can be drastically reduced. This improvement The second
in the ratio of signal
and
third advantages
to noise is particularly
can still be gained
valuable
for daylight
(even in cases where
ranging.
an accurate
timebias
is
not available beforehand) if the first few good returns from the satellite are used in real time to convert a range offset into a timebias correction. This technique is routinely applied for multiphoton detection systems where the identity of true returns is not in doubt. But for single photon detection in daylight, or using an intrinsically noisy detector such as a SPAD, it is not always easy for the software to pick out the track, and some form of manual intervention may be required. Where
can
Originally
we
get
timebiases?
we used only our own history
of passes to make extrapolations
to current
behaviour:
Tl_is
was quite satisfactory during periods of continuous good weather, but was often very frustrating when trying to recover satellites _ter a break of two or three days due to cloud or instrumental problems. Then, for Ajisai and Starlette, we tried using Bendix's timebias data from many stations in addition to our own. We immediately found a great improvement in the quality of our extrapolation and could use narrower range windows right at the start of the pass. We also found that the change from using elements to using IRVs gave better consistency in the timebias histories. When EILS-1 was launched we, like everyone else, had mixed success in finding
it.
When we
had a reasonable history and the solar activity was not too wild, we got good passes. But at other times, once we had failed to get passes for a day or two, it became increasingly difficult to recover the satellite. We were very pleased when DGFI _reed to use the pass data that they receive from many stations to produce timebias functions for EILS-1. This gave, and continues to give, valuable additional
weight
to timebias
trends,
,il,001
v
[-.
87 g_
I
!
I
i
I
_
[]
RGO
x
Potsdam
•
Santiago
0
de
Cuba
Graz
o o I
I
i
48720
i
i 48722 Julian
48724 Date
48728
Figure 1: ERS-I timebiasesfrom EDC
9-14
for IRV setA920,_07 and symbol key
Since
then, following
the
establishment
of the European
Data
Centre
(EDC),
a small
stations have begun to make regular deposits of their timebias data for ERS-1 observations. We often get EDC data from Graz and Potsdam--and occasionally
number
of
soon after the from %Vettzell
and Santiago de Cuba. Figure 1 shows a plot of the data deposited for IR.V set A920407 at the beginning of 1992 April. The interagreement between the values from different stations is striking and gives great confidence that all timebiases have been reduced to a common system. But, with all the stations close together in Europe, it is clear that the data are clumped together in time: indeed, sometimes they are all clouded out simultaneously! The addition of more data points from other stations
at other longitudes
How
can
we
best
use
around
the world would give mucll better
timebias
"round
the clock" coverage.
histories?
1
EB.S-1 timebias
Over the last two or three months we have been investigating how best to predict future values from whatever timebias history we ha_l available on a particular day. This usually
consisted of a small number of values covering a few days. First we looked at the timebiases shown in Figure 1 which cover a period of about a week and are all referred to the same IRV set from DGFI. Our approach was to see, in retrospect, how well the observed values available up to a certain day could be used as predictors for the points which followed. The results of our trial fits are shown in Figure 2. First we fitted to data for the first two days only; next we used data for the first three days; then the first four days and
__'-_A.'
O
'
'
I '
'
' /II'
II[I_
O O
O
O O
•....
I
:S
7 $ 7 $ T
,
E O I
-,
I ,
,
48720
I,
,
,,
48722
°,
_ tXl
48724
48726
I,
For each
O
O
E
v
so on.
i
"'-
, I , 48720
, , , , , I , 48722 48724 Julian Date
Julian Date
°
48726
°:,
r_.l
, '
,
I
' '
' I
'
'
'
I ' -
O
o
7
'_,.
:
I
i-r.
,;._.
i
-
{W I O O iv) I O O
O I
O
-,
I , 48720
, i I , _ I , I , 48722 48724 48726 Julian Date
Figure
2: Successive
fits to ERS-I 9-15
I
t
48720
timcbiases
48722 48724 Julian Date
from
EDC
_,.
kxj 48726
--
trial we fitted
the data
with functions
of three different
orders--linear
(represented
by a solid line
in Figure 2), quadratic (dotted line) and cubic (dashed line). Only points to the left of the vertical arrow at the bottom of each plot wcre included in the fit. We then looked at the next few points to the right of the arrow to see how well, or how badly, each of the attempted data which followcd. From this examination we drew a number of preliminary • Use the simplest fit)--it
function
will generally
• Use only linear
wlfich gives
be better
a reasonable
fit to the data
for extrapolationthan
fits for the first 2 or 3 days--there
a higher
(even
order
are too few data
fits represented conclusions:
the
if it is not the
best
function;
points
to justify
anything
fancy; • It would coverage.
be helpful This
to have
quick
o fill the gaps in the Europema o add data o provide
timebias
deposits
by all stations
points
longitude
actual
timebias
the fit;
values
closer to the time of observation
in the Bendix
timebiases
use in revealing a week in early
than
are avMlable
now.
based on normal point data for EKS-1 passes extracted to give timebiases. [We had hoped to use directly the
Bendix values, but there are currently unexplained discrepancies between tlmebias and ours, so we have worked entirely from the normal point data. prevent their which covers
better
data;
to strengthen
More recently we tried a new experiment from the CDDIS database and reduced
to exist
and
would:
for Ajisai
and
Starlette,
but
their derived values of This effect also appears
to a lesser extent
which
does not
long-term trends]. In this case we took the data set shown in Figure 3 May and is referred to IRV set A920505 from DGFI. It is clear that _---]-_--iiiiiiiII1'""'1111_ O O B
t_
E
B
v
oo E 0 O
48748
Pigure the longitude is a drawback
3:ERS-1
48750 48752 Julian Date
timebiases
from
CDDIS
48754
normal
points
coverage is more uniform and the daily density of points is higher. However, there as far as immediacy is concerned in that the turn round time for data input can
be longer than for EDC, so procedure that we used for well the extrapolated curves Figure 4 again show that the
that some of the data are relatively old. We then followed the same the EDC data and made trial fits to subsets of the data to see how acted as predictors for what was subsequently observed. The plots in higher order fits are wildly ineffective for the first few days, and only
begin to make more sense later. But around day 48752 the data take a wholly unexpected turn towards large positive values and the trends evident in the early points are no longer relcvant. This sudden change of behaviour is probably due to solar activity, andin such circumstances it is wise to abandon the early points of the data set and start the fit again from part way through.
9-16
'
oo
I '_
(w
'
'
I
i
.
I _ ° ° I ' J ' '-[] I in
-4 []
-I
I
, I, g
oo
I
,
,
,
I
,
[]
, j 11
I
I A
I
E
!
\
o_
o
I
I
[]
o
48748
48750 Julian
48752 Date
48754
48748
4{]750 Ju]ian
48752 Date
48754
o O O3
.--.
E
_-' I
'
'
'
I
'
'
'_/'
'
' '[]I
_
v
J
[]
/--
/
o-_
/
4
/
E []
[] / /
.. 13
o
./'"
0
48748
48750
48752
...*''"
48754
48748
Julian Date
Figure
Our
_:dditional
4: Successive
fits
as a result
of this
conclusions
•
For El%S-1 it is necessary to examine pected trends in good time;
•
Better
•
Access to the any functions!
Ajisai
and
longitude
coverage raw
data
Starlette
is essential is very
Generally
exercise the
data
from
48752 Date
48754
CDDIS
were: functions
warning
for making
prediction
timcbiases
and
for early
useful
the
to ERS-1
48750 Julian
value
d'aily
in order
of departures
from
judgements
of timebiases
for
on
these
the
to pick
previous quality
satellites
up
unex-
behaviour; of the
is much
fit of
more
straightforward than for EllS-1 since they are relatively unaffected by atmospheric drag and solar radiation pressure. Indeed orbit predictions can run quite satisfactorily for several weeks so that a long timebias history can be established for one II%V set. Over such an interval timebias corrections usually to one What
behave sensibly and, even when the corrections get quite large, a good set of IllVs allows meaningful extrapolation to get accurate values. can
We think trends in possible
be
done
to
that all stations timebiases for after
the
pass
with
respect
improve?
can EllS-1
has
history
share the clear by depositing
ended.
Then,
benefits to be gained their timebias values
by retrieving
9117
a comprehensive
from with
the daily examination data centres as soon set
of timebiases
of as
obtained
==
worldwide, and using itas the basisforextrapolation, the "hitrate" can be significantly improved. Alternatively, but probably with greaterdelay,stationscan retrievenormal point data and derive timebiasesfrom .them. Itwould be very worthwhile to extend the system to includeAjisaiand Starlette; and to make sure that provisionismade forrapid feedbackof Topex/Poseidon data. Finallythe proper commercial: we think that timebiasesarejustlikewashing powdcr--use the rightone and your whole lifeis transformedforthe better!
Figure
5: "Net# improved
Timebias _
Acknowledgements We
wish to thank the staffof the predictionand data archiving centresfor advice and data.
Specialthanks go to Brion Conklin of Bendix forhis speedy and cheerfulresponsesto our many requests.We greatlyappreciateassistancefrom Rolf Koenig of DGFI and Wolfgang SeemiiUcr of the European Data Centre.
9-18
N94-15592 Formation
of on-site
Normal
Points
G.M. Appleby and A.T. Sinclair Royal Greenwich Observatory Madingley Cambridge
Road
CB3
0EZ,
UK
Abstract. We
describe
from
our
methods
a predicted
directions.
orbit,
The
predicted
orbits
analytically
of fittin 9 a smoothin by deducing
method
has
computed
from
been
9 function
corrections used
on
elements.
The
to the
orbit
observations
both by numerical
orbital
to observational in the
of a variety
integration
along-track
differences
and
along-track
radial
of satellites,
usin 9 [RVs
corrections
range
and
as startin
to the
using
9 values
and
orbit
have
predicted
been succesfully used in the form of time biases to improve subsequent predictions, and a statistical test has been devised to ensure that the range residuals may be used to form unbiased quicklook
normal
points.
1. Introduction. It was
recommended
at the
Fifth
International
Laser
Ranging
Instrumentation
Workshop
held at Herstmonceux, UK, that laser range normal points should be formed by the stations shortly after each satellite pass and transmitted as quicklook data (Gaignebet, 1985). The final
version
of the
the CSTG The
quicklook
and published
process
of forming
normal
to the observational order to form a flat
range track
mean
accepted
values
smoothing
of the function
normal
point
in the April
and
points
differences of residuals,
consists
predicted
orbit
of the bin are then added points are then virtually
of the
orbit.
In this report we detail for rejecting noise and (these 2.
by the
Ranging (a)
SLR
Subcommission
Newsletter fitting
spread
at the
through epoch
to the mean independent
the
(Schutz,
a smoothing
pass.
of an actual
of 1990).
function
the function and forming The
values
observation
of the nearest
value of the residuals in the bin. of both the smoothing function
the processes adopted to carry forming unbiased normal point
in the
The and
out stage (a) of the process; methods bin means are developed by Sinclair
proceedings)
Development
of the
During the observation for all events detected appearing example gross
Laser
of 2 stages;
in bins
the mean epoch resulting normal predicted
was agreed
from a predicted orbit and subtracting and (b) rejecting noise and outliers
residuals
the
format
1990 Satellite
as a track of such
noise
events
Smoothing
Function.
of a satellite pass, differences from within the range gate and displayed I
of correlated
a plot
is given
is carried
out
values in Figure visually
among
the
1, which using 9-19 '
the
the predicted in realtime,
randomly shows plot,
distributed
a pass and
range are computed true satellite returns
the
of ERS-1. subsequent
noise
events.
The
rejection
set
An
of satellite
of
range
measurements
At an early to use
the
stage
and
events
are passed
development
of the
observations
to s61ve
the
along-track
to orbits
similarly
to the
preprocessing for
error,
next
stage
software,
corrections
in order
of processing.
the
to the
to improve
decision
was
predicted
orbit,
subsequent
correction
computed
corrections
orbit
during
can be expressed
by numerical
to the
IRVs
integration
would
not
the
solution
as an orbital
iteration
and
using
be applicable
time-bias
process,
computed and stored. For each observational tion to compute the instantaneous position
and
for improving
the prediction process an orbit in the form and velocities at 1-minute time intervals
generated
by numerical
respect to the true analytically-derived equinox station the
equator orbit,
IRVs
as starting
to orbits
computed
the
derived
subsequent
of geocentric and in units
along-track predictions.
rectangular of Mm and
satellite Mm/day,
epoch, we use 8th order Lagrangean r and velocity v of the satellite. Let
predicted
topocentric
predicted range of the observed
predicted
orbit and
2.2
Derivatives.
Partial
(a) Let Then
radial
the along-track the
displaced
using
IRVs,
the
coordinates
partial
components
of this range,
interpolar = (x,y,z),
are
given
=OR v_(x
+ v_AT-
ZT = z -- Zs
,
topocentric vector. We thus form and in order to solve for corrections
of range
with
respect
of the predicted
to the
along-track,
orbit.
be AT.
by
xs) 2 + (y + v_AT-
xs) + v_(y
or approximately
9-20
with
epoch of the IRVs. For an to the mean equator and
ys) 2 + (z + vzAT--
Zs) 2
Then
R.._-_-_
The for
are
displacement
or time-bias
R is given
R 2 = (x + vzAT-
satellite
derivatives of the
cois
we compute the coordinates of the observing station coordinates be s = (zs, y,, z,). Then
YT = Y - Ys,
is the magnitude from the predicted
displacement range
of the
= X '--:-Xs,
we require
across-track
and
epoch, Let the
coordinates XT
the
integration
and mean equinox at 0hrs UT of the the coordinates are given with respect
of date. At the observational in the same reference frame.
and the difference
and
prediction
and v = (v,, vu, vz), and let the magnitudes of these vectors be r and v respectively. reference frame used is different depending upon the source of the orbit being considered; an orbit
taken
Thus it was decided to express orbital corrections as along-track, across-track displa_:ements to the predicted position. Such corlections are then readily applied
geocentric
During ordinates
noise
the possible use of an arbitrary polynomial for the smoothing function was However, corrections to the predicted orbital elements of the satellite would
to apply
analytically. and radial to the
of the
to monitor
accuracy. Thus not considered. values,
some
pass-by-pass
in particular
be difficult
and
+ vyAT-
y,) + v_(z
+ vzAT-
z,),
the to
OR OAT (b) Let The
the
across-track
across-track
= (V=ZT + vyyT
displacement
direction
+ VzZT)/R
be A Q
is rXV
= (l,m,n)
, say.
r-v
So_
l = (yvz- zv_)/r_
n = (xv v - yvx)/rv So the
displaced
range
R is given
n 2 = (x + IAQ
-
by
z,) 2 + (y + mZlQ
-
y,)2
+ (z + nAQ
-
z,) 2
So_
OR RcOAQ
= l(x + lAQ-
z,)
+ m(y
+ ,nAQ
- y,) + n(z
+ nAQ
-
or approximately OR OAQ (c) Let
the
radial
displacement
So the
displaced
coordinates
So the
displaced
range
-
(l XT + m YT A- n ZT)/R
be Ar of the
R is given
satellite
are
x + zAr/r,
etc.
by zAr
R2 = (_ + _____5_ _ x_)_+ (y + yAr __ _ y,12+ (z + --r r
Then
as before
we calculate
r
the
approximate
partial
derivative
OR
o3r = (__r + yyr + z zr)/(_R) 9-21
-
z,) 2
z,)),
2.3
Solutions.
In practice the radial not
it was found that the across-track correction was always highly correlated correction, and in many cases the solution was indeterminate. Hence both
be solved-for,
for a radial found
and
that
simple
in general
decided
which
to suppress
would
along-track
all the error
derivatives
parameters
only,
constant
absorb
for a particular pass time rates of change partial
so it was
correction
and
of range
with
and
solution the
corrections that
to the
rates
of the constant
to the predicted
of change
terms
necessary
were
to solve
required
for only
to remove
4 of the
all trends
from
possible
the
Initially a scheme was devised to automatically among the 4 unknowns _h, _,/_,/_, and to supress determinate
solution,
consistent
with obtaining
their The
of these
by t and
but
t 2, where
occasionally
all six
residuals.
check for very high (>0.999) correlations any one or two of them in order to obtain a flat
track
of residuals.
accelerations. parameters,
imposed a-priori standard errors of these the program to solve for all six unknowns.
In order satellite
did not
accelerations
six parameters,
determined for 2h and
We thus allowed
also
of the pass. Such a definition the unknowns. It was usually
showed that the values order of 0.1 ms/minute and
orbit
displacements.and T, T, T, R, R,/_.
and
solve
It was
to be determined
by mutiplication
observational
and
error.
the set of parameters
time t is the epoch of each observation relative to the mid-tlme for the origin of t is optimum in reducing correlations between found
for across-track,
across-track
from along-track and radial We denote these parameters
respect
from those
the
absorb
radial
in the orbits,
should be selected and accelerations.
were formed
thus
with could
for these 4 parameters 1.0 cm/minute for R,
However
were always and of similar
a
experience
quite small, of the magnitude for the
magnitudes
to iterate the solution, at each stage we replace the predicted by the displaced coordinates as determined from the previous
upon
coordinates solution.
the
4
of the So for
example
x = x + vzAT and
similarly
outliers
for y and
of magnitude
A selection
of some
z.
It was
greater plots
than
check
a single-factor
that
the
analysis
that
these
track
removed
residuals
residuals
test
is indeed
on
the
were
at each
is given
are readily
of residuals
of variance
+ xAr/r
4 or 5 iterations
3 x rms were
of observational
all trends have been removed; the Herstmonceux algorithm. As a final
found
+ IAQ
usually
2, where
to form
statistically
residuals.
This
where
stage.
in Figure used
sufficient,
flat, test
it is clear
that
points
using
normal
we have checks
introduced
for significant
differences between the means of residuals grouped into normal point bins; any differences indicate that not all trends have been removed from the residuals, and a warning is given that
normal
anticipated during
points that
this
should test
not may
be formed prove
useful
until
the
for the
a pass.
9-22
cause detection
of the
problem
of system
is traced.
calibration
It is changes
3. The
Conclusion. scheme
was
found
to be determinate
for a wide
range
of satellites
and
pass
durations
and quality of predictions, and has been adopted at Herstmonceux. An earlier version of the software is also in use at several European SLR stations. The deduced values of time bias are used has been
to good effect for improving subsequent used to generate time bias values from
stations,
as described
4.
by Wood
and
Gibbs
(these
predictions, the quicklook
and additionally the software observations from other SLR
proceedings).
References.
Gaignebet, on Laser Schutz, University
J. (Ed) Ranging B.E.
(Ed)
of Texas
1985.
Recommendation
Instrumentation. 1990,
84A,
CERGA,
April
Satellite
at Austin,
USA.
Laser
9-23
Normal
Points,
in Proc.
5th Int.
Workshop
Center
for Space
Research,
France. Ranging
Newsletter,
-
0 0
la0 °,,q
!
°
•
0 0 0
0 0
(su)
0
I_?npTsa_ 9-24
0 O.
a_ue_
i
0 0 O_ I
.4
.2 _° o" .
o
.
° o.
"..
.
° .
•
•
....
•
o
.°
.
o
".•
•
°* • °. °
•
.
°
.
• ° .:
°.
.°
• .,'._
"t......°
• ::.-...._.-., ... • .......
o : ...
•
• °
.-._ .'...
• ...
". ° .° o ° °° %. ; ; ° ..
.
...
•
° .o
.
•
.
:'." . .'_ ., ...; ...
.
• °
. o.." •
0 .. - .....
,..°_
": _ '.:. -'°.."..'.°.. • " "." :: • '
w
""
o°
o_
.o
.L•
. •
.."
.'...._
-"'.A,
t*
.:-_ .°
•
-°.':.
.° •
D •
'
"."
" °"
'T"x;
".'" o"._ _ .,_''_." q : "_'.. "."::°._ ": ."....'" .'...,."t ..... "' " " ". " • "" '" ." -" %'.-"F" :_
•
"
•
"
•
•
•
..o:
' "'" .:" •
°
i
"
-.2
-.4
I
I
,
I
I
I
3550
I
I
I
3600
,
,
I
,
3650 (secs) ERA
Time
,
,
,
1 i
j
,
281.
I ,._____
3750
' I''
r-
4
_ I
3'700 (SPAD+HP)
'-]_--_-_-_j
i
7/
i
2
_, -r.
-..
=
..
°
.
,.
•
. •-
,
•
°o
°
•
.
°°
•
. o.,:..-'.:.'o:::.-.[...:..¢ ;.... • :; _._,.._; • ...I.._...: -..-,..
•
:.....
* o
.
,
•
......-.. ."....
..
_ ,'" ". "".-.:_'",'>'.."_"_,(,:. ':,;')!.'.'._",'L_ e"7"" _._ ;'.:.:.
I
°
•
,
_%.e**• •• . * •.
_
•°
"_
*" • "° . • .. •
•.'-";'": :,.4 *."
_0 •
.
;
t
"
°..
•
w,.,
.,...
s,
*t:..'_*-.%.:.'e?_._
.-;_..2.._._. "'" * _l"
.. ."
"%*¢'*
;_¢_:.*..o::_,..*-.
.,. r.. ,':>_.,-,_,._:._j,-_-.'_.._?; -,__,._.#T_, _._'£_':."",_,_".;:.:."_ L: .,".-_,• • .._.::,." "*'-(': .V :"' ":". _:'._-;",,.:;_'. • • ' "2_
|
-_
__.
-.4
_.o_,.... .,
i
,
•
• °
•
•
•
,,. ."
* .,..' . _
,
s
,.-.o.,
*
•
.
"
,r
°
.%
•
.
,T
•
°
m!
•
'.L"..,,
_' • _
:* "" • "...
;'_.. " _. "
. "
",._ ":
""
• _ _.:; ;.,
.'.V:2.• " ".
•
*,
' "
: i ij
4200
Figure
4400
2. _ange
i ,_'_ 4600
residuals
4800 Time
from
: ,I ; ,. _ i ____1 , 5000 5200 5400 (s) L-_G 236
a pass 9-25
of ERS-1
l
I
"
(b) :.L_J
t
••" •
(a)
_ i 5600
,. ; ;
,_,.__
5800
a x/d Lageos
6000
(b).
Poisson
Filtering
of
Laser
Ranging
Data
by
McDonald
R. L Ricklefs and P. J. Shelus Observatory, University of Texas, Austin, TX 78712
The filtering of data in a high noise, low signal strengthenvironment is a situation encountered routinely in lunar laser ranging (LLR) and, to a lesser extent, in artificial satellite laser ranging (SLR). The use of Poisson statistics as one of the tools for filteringLLR data is described first in a historical context. The more recent application of this statistical technique to noisy SLR data is also described.
Introduction Routine LLR operations began at McDonald Observatory in August, 1969 as a part of the NASA Apollo Lunar Ranging Experiment (LURE), using the newly-commissioned 2.7-m astronomical telescope to range to the retro-reflector array placed upon the lunar surface by the Apollo 11 astronauts. During the next several years, additional arrays were left on the moon during the Apollo 14 and Apollo 15 missions, and by two Soviet unmanned soft landing vehicles. Routine LLR operations continued on the 2.7-m telescope until the mid-1980's when these operations were transferred to.the dedicated 0.76-m aperture McDonald Laser Ranging Station (MLRS). It is important to realize that the return signal strength ratio, neglecting all parameters except distance, for a near-Earth artificial satellite and the Moon is something like 3 x 1012. Thus, it is more than a trillion times more difficult to range to the Moon than it is to range to, say, Ajisai. In the extremely low signal strength environment of LLR it was (and continues to be) necessary to operate largely at the single photon-electron level. However, this means that a very large number of "volunteer" photons from any number of background noise sources may trigger the detection electronics, even though very narrow spatial, spectral and temporal f'flters are routinely employed in the receive package. Since all incoming photons are indistinguishable from one another, identifying the valid returns from the moon has been a difficult task. From this experiment's inception, the reliance on statistical f'fltering methods, in addition to the physical ones, had been always assumed. The application of Poisson statistics to the LLR data filtering problem provided an effective tool for dealing with high-noise, low signal data. The technique has now been expanded and adapted to handle marginal SLR data as well and has proven to be especially effective when applied to data from single or low-multiple photo-electron systems during daylight passes and data from all stations when they are ranging more difficult targets like Etalon- 1, Etalon-2, and MP-2. Figures 1 and 2 show samples of noisy data, displayed by MLRS onsite software, for which the Poisson technique is required.
Background Let us consider the mathematical concept of the Poisson distribution, which gives the probability that a certain integer number, k, of unit rate random events from a population, n, will occur in a given interval of time, x, within some total interval of time. The operative equation is: 9-26
P(k) -
x[k] e-X [k]!
where [k] is the largest integer less than k. For x large enough, this function has a bell shape comprised of many rectangular steps. Multiplying the computed probability by the number of bins in the entire sample time gives the number of bins which contain exactly k events. In a descriptivesense,Poisson statistics statesthatffone has "n" observationsof some independent variabledefined over some range of "m" bins of uniform width, and ifthose observationsarc random, one can compute, in a statistical sense,how many of those bins will contain exactly k observations. For example, for some specificexperiment of,say, 16 independent observationsof some value,one might compute from theabove equation that 3 of the bins will be empty, 4 of them will contain exactly 1 observation,3 of them willcontain exactly 2 observations,2 of them willcontain exactly3 observations,and no bins will contain 4 or more observations. Then, ifone looks at the actualhistogram of measurements and findsthatone of the bins contains8 of the 16 observations,one might safelyassume thatthose observationsare indeed not from a random distribution and that something systematic has occurred. In the case of LLR or SLR observations,where the measurement is an (o-c)range residual,itis assumed thatthe bin (or bins) containing a statistical excess of observationsarc probably valid returnsfrom the targetor theresultof some systematiceffectin theranging equipment. As another example, figure3 represents the statistics from the lunar data in figure I. The predictionsindicatethatthere should be no bins with more than 21 points. One bins has 22 points, which is probably not significant, but thereis another bin with 47 points,which issignificant. That bin contains the lunardata. This technique is routinely applied to thc filtering of McDonald Observatory LLR data and is fully described in "Laser observations of the Moon: Identification and construction of normal points for 1969-1971 by Abbot, Shclus, Mulholland and Silverberg (Astron. J., Vol. 78, No. 8, pp 784-793, October, 1973).
Current
state
of
affairs
In the routine application of the Poisson technique to data filterin.g it must be noted that, in order to have the best possible chance of isolating signal from norse, one should use the narrowest bin width possible, keeping in mind at all times, of course, the quantity being measured. Narrow bins will maximize the signal to noise ratio since, in a narrow-bin environment, a relatively small number of noise photons will be found in any one bin. Further, it is absolutely required that the data be flattened before a histogram is formed, i.e., trends must be removed from the data as much as is possible, so that signal will not "spill over" into many adjacent bins and, again, be lost in the "noise". This problem has been addressed in a straightforward way in the current data screening implementation at the MI_S, as shown in figure 4. All bins are scanned sequentially through a predetermined range of slopes, the plan being that the signal will appear at a significant peak at a slope that matches the inherent slope of the data. This technique is especially important for LLR data when signal strength is low and for SLR data when orbits arc not well known. Of course, in altering the slope of the data, one must take care to exclude, or compensate for, those bins which will be incomplete due to clipping. In its present implementation at the MLRS, the Poisson screening software also allows multiple segments of a pass, or a run, to be treated separately. This handles the natural change in residual slope over an extended observation session. 9-27
Although personnel atthe MLRS arc now applying the Poisson filtering technique for both lunar and artificial satellite data,the LLR and SLR screeningsystems are somewhat different. Both systems provide user interactionto allow the selectionof the parameters of the Poisson fit,placement of the time bins, maximum and minimum slopes, and a maximum 8nd minimum residualfor data to be accepted as "real'_.For lunar data, wc employ fairlystrict limitson acceptableslopesand allowable residuals.Earth rotationand polar motion are major contributorsto slope and residualfor lunar data, so the earth orientationpredictionsarekept as freshas possible.Further,thereisconsiderablelatitude in selectingtime bins to reflecttheobserved clumping of NR,RS LLR data. Ultimately,the Poisson filteris reliedon to provide the LLR data compression, i.e.,normal pointing, softwarewith a setof acceptabledata. For the SLR case, the Poisson algorithms serve as a preliminary filter and suggest to the polynomial fitting algorithms in the normal pointing packages a set of data with which to start. The polynomial fit, in its job, can then return previously rejected data back into the fit or remove data suggested to it by the Poisson filter, if either of these tasks arc warranted. Also, the polynomial fit, working on the entire pass, can pull in data that might be missed or misinterpreted when the Poisson filter was working on only shorter segments of a pass. The independent time segments, into which an SLR pass is broken, allow the software to follow changes in slope during a pass and minimize the effect of anomalous distributions of data in short segments. We are examining the desirability of having several software checks that require the slopes and average O-C residuals to be smoothly varying over the pass. However, in the cases where there are breaks in the data and other unusual distributions, this may not be practical.
Results In the case of LLR data,the presentlyimplemented Poisson filtering technique works well,especiallywith a bitof interactivehelp from the user,although,in marginal cases,it would be preferableto use allruns taken over a lunar pass to aid in the filtering.This particularextension isnow being examined. As time permits we arc alsopursuing more elaboratefiltering techniques such as jack-knifingand bootstrappingto see ifthey hold merit. In the case of SLR, the technique has been used successfully at MLRS for about a year now. In that time our experience has been that the combination of the Poisson filter and the polynomial fit produces good results virtually all of the time. The marginal cases can usually be satisfactorily processed, after the fact, by altering some of the parameter of the Poisson fit or by eliminating from consideration extremely noisy parts of the pass. Of course, most of the anomalies usually occur with weak passes, especially Etalon- 1, Etalon2 and ERS-1. The Poisson filter algorithms are being upgraded so that each satellite uses a parameter set tailored to it. Tests indicate that this will allow successful batch processing of virtually all passes that previously required special handling. Also, an interactive tool similar to the Lunar Data Editor is being developed to help the observing crews to quickly recover passes that were improperly processed. The Laser Tracking Network operated by the Bendix Field Engineering Corporation will soon install the MLRS "batch" Poisson code into their processing software.
9-28
Conclusion The Poisson filtering technique has proven itself to be an extremely valuable tool for both LLR and SLR operations at the MLRS. This technique is being optimized for each ranging target, and in the future provision will be made for routine, near-real-time observing crew interaction with the filter. In addition, new filtering techniques such as jack-knifing and bootstrapping will be evaluated as to suitability for laser ranging data filtering.
9-29
rd.p File
Edit
Graph
Iot
Enlarge
Help
OC Residuals O-C
(rmc>x
x
x
1,4_ x
x 1._
x
x
1._.
x
X
i_
X X
1.0_
X
x _x x_ xX Xx
x x
x
1.1'.
T_ x
>:_
)4,x x
_x
_< xx
x
X x
X
)4z_xX
X xx
.
x
_< x x
x
_x_
x
x
x
_
x
x x
X
0._
x
X
X X x
x
x_x x x
X
XKX
X
x
x
x XX
XXx
_x
X
x
x
X X
xx
X X
x
X
X
X
xx
x
x
x
x
xx
X
X xx
xxxXx
x xX
0.R
X
XX
X>
X
X
X
X
X_x
_
x
x
X xKX
x>:
x
XX
x X
X
X
XX
X
0.4_
X _
XXxX
x
0._
x
X
x x
_
x
x x
x
xX
x
0.05 -0._
>o
10
W
L..
I1)
E = z
5
0 0
10
Figure 1: Histogram of the 'semitrain 1991. The session lasted 15 minutes
20
30
Range
Residuals
ranges'
to APOLLO
10-16
40
50
60
the night
of Nov. 25th
[ns]
15 during
Fixed Station Upgrades/Developments
N94"15601 MATERA
LASER
RANGING
OBSERVATORY
Thomas
Varghese,
Winfield
(MLRO),
Decker,
AN
Henry
OVERVIEW
Crooks
Allied-Signal Aerospace Company Bendix/CDSLR Network Seabrook,
Maryland U.S.A.
Giuseppe Agenzia
Spaziale
20706
Bianco
Italiana/Centro Matera,
di Geodesia
Spaziale
Italy
Abstracl;: The
Agenzia
Bendix Company Centro
Italiana
Engineering
(ASAC)
telescope
future,
with
with
a specialized
on a 1.5
multiple
dome
which
The
fixed
locating
the
following:
and the operations concrete
for
pad for
minimizing power
the
laser
fitting
The
is currently
scaling
or changes
system
with
system.
Provisions
with
Signal
a variety
for the
calls
for
the
astronomical
of experiments
Three
the
Aerospace
observatory
contract
Cassegrain
ranging.
console. added of
The
EMI,
transmit
focal
planes,
for viz.
the
be highly
It is conceived specifications
also made
to adapt
course
for
areas
for
telescope/dome and mount
Provisions maximum
providing
rest on will be in
cleanliness
an ergonomic
laboratory.
modular
and
adaptable
to be a highly to any currently
and accommodate
of design
ii-i
tables
obtaining and
to be provided
into four
stability.
multipurpose to
facilities optics,
optical
for
optics,
designed
performance are
building
be partitioned
mechanical
in technology.
during
will
transmit/receive
to a state-of-the-art
superior
are of significance
facility
effects
and
environment system
to support
on laser
laser,
a common high
The
afocal
will be part of the
observatory
enclosure, place
negotiation
Allied
laser ranging Italy.
meter
ports
emphasis
under
of the
and Nasmyth will be available for these experiments. system will be protected from dust and turbulence using
by ASI.
for
(BFEC)
in Matera,
based
primary
Cassegrain, Coude, The open,telescope
is currently
a state-of-the-art
Spaziale,
of a system
quality
(ASI)
Corporation
to build
di Geodesia
delivery the
Spaziale
Field
and integration.
for
automated operational
changes
that
MLRO Objective:
:An Overview
Build a state-of-the-art, multi-purpose, observatory in Matera, Italy
laser ranging
General Features I
Day and night automated
ranging
capability
on all CCR-equipped
satellites
(> 400 km) and the moon •
Application
of state-of-the-art
•
Real time calibration
•
Multicolor
ranging
•
Advanced
computing
•
Computerized
documentation,
expert
and hypermedia
system
technology
and interleaved
in all sub-systems
multi-satellite
tracking
and data analysis
tools
capability environment
with features
such as relational
text
System Specifications LAGEOS
ranging" Single
shot precision
• --5 mm
.Normal point precision Low orbit satellite
(ERS-1,
Single Lunar ranging
• Single shot precision
Single
i
Range
Starlette,
shot precision
Real time calibration/ground
accuracy:
• < 1 mm
• 3 - 5 mm
• -1 cm
ranging
shot precision
etc.) •
•
• =10 Hz
Computer
controlled
Modularity
seeding
for energy
Laser firing stability
beam divergence scaling
/ multi-wavelength
: better than 20 nsec
11-3
generation
MLRO
:An Overview Control
D
Software
D
Automatic
recording
Automated
star calibration,
in high level languages
Computer-assisted t
Distributed
D
Advanced
System
Automated
of all operational
optical
parameters
mount modelling alignment
data acquisition,
and verification
processing,
computing/control
environment
system/sub-system
simulation
Transmit/Receive D
Detection"
and debugging
Electronics
High Q.E, high speed MCP-PMT/APD
Signal processing
:
Speed
: 1 - 5 GHz
Dynamic Jitter Event
and control
range
: 20
:
ca
1 ,//
/ !
co t'i__J l--
t..la
o 0
.la o
._I ,-4 u c _0 o
......
k
O*J u_
12-23
Decrease
of MTLR,C #1
r.m.s
r.m.s in ns
r.m.s
in cm 10
0,5
[]
r,m.s in n8
I
9
r.m.s in cm
I
8
0,4
7 6
0,3
5 4
0,2 []
3
[]
2
0,1
1 I
old
I
new Laser
Fig. 4: Decrease
R.M.S, r.m,_,
new Start
of the
single
0
I
Receiverpa(-k
shot
r.m.s,
of MTLRS#1
during
SPAD
upgrade
Components
ps
In
I I 400
300
100 200
65 i
3O
lO0 20 0
0
I
La=er
Fig. 5. Single
START
shot
.....
_
I
Recelverpack.
r.m.s
before 12-24
STOP
and after
Counter
upgrading
typical
Lageos
nighttime
pass
(PMT)
before
upgrading
_.._
"T
_-- -.q8._._4
ns
Pre Calibration
Post Calibration •
I_V_.._._.
_"
typical
--
Fig.
....
• • ._
:.
-,
Lageos
.._
_:,_:_,.
':_,-. - _ L,-_.
_.'.v.,_-:,-
_ "...:
.
•
:
day/nighttime
_
_:_]
,.
.
pass
.,..,
Lageos
Pass
before
and
after 12-25
_._:_.-.
(SPAD)
-e@eS@@r,s
-
..
upgrading
after
upgrading
N94-15611 The
new P.
MTLRS_I
SPERBER,
INSTITUT
Receiving
U.
FI_R
HESSELS,
R.
ANGEWANDTE
MOTZ,
GEODASIE
FUNDAMENTALSTATION DER
System
WETTZELL
FORSCHUNGSGRUPPE
SATELLITENGEODASIE
D-8493
K()TZTING
H.-M. GI.iTHER HOECHST AG, MATERIALFORSCHUNG D-6230 FRANKFURT AM MAIN 80
Abstract. In this
report
Transportable
we are giving Laser
and
a Single
and
night
Photon
ranging
a detailed
Ranging
System
Avalanche
capability
description
Diode to all
of the
MTLRS_I (SPAD)
satellltes
new receiving
consisting aa single
with
cm
system
of a spectral photon
of the
time
detector.
and
The
German field
system
Modular
of view gives
filter
full
day
accuracy.
1. Introduction In order to improve the ranging accuracy and the sensitivity of the German Modular Transportable Laser Ranging System MTLRS-1 a major system upgrade was scheduled and performed from Dec. 1990 to July 1991 (P. Sperber et.al•). mitting part (Laser and Start Diode) (P. Sperber was the main point of the upgrade. The receiving
2.
system
•
Filter
(Frequency,
•
Single
Photon
Receiving To extract
mainly
has two parts, Range,
Together with the exchange of the whole transet.al.) the installation of a new receiving system
which will be shown
in detail
Field of View)
Detector.
System reflected
in daylight,
This filtering
photons
fr6m the satellite
from noise photons
which are entering
filter eqmpment
has to be installed
in SLR systems.
a powerful
in modern
systems
is realized
the telescope
in three steps
•
Range (time interval) filter: A rotating shutter is commonly used to supress straylight during laser firing and to open the detector at the time, the echo from the satellite is expected.
•
Field of View: A pinhole ensures, telescope axis can hit the detector.
•
Spectral just
Filter:
The most
effective
light of the well defined
that
only light
filtering
laserwavelength
process
coming
from a small
is the filtering
angle
in frequency
the
which allows
to propagate• Typeset
12-26
around
by .AA45-TEX
The new receiver package of MTLRS#1 requests, deliverd by Technisch Physische The setup is shown
is a very compact, field qualified realization Dienste (TPD), Delft, Netherlands.
of this three
in Fig. 1.
The light from the telescope is focussed to a field of view pinhole, which a motor driven micrometer from 0 to about 30 millidegrees. Connected there is a rotating shutter, synchronized to the predicted system 10 times per second for about 3 ms and mainly straylight during laser firing. The spectral filtering is done by an echelle
grating
is remote adjustable to the field of view
with filter
range window, which opens the receiving protects the single photon detector from
(efficiency:
55 %) used in 7 th order,
which
gives a bandwidth of 0.2 - 0.65 nm depending on the opening of the filed of view pinhole. The grating has a surface of almost 100 mm top-top in air, therefore the range difference of the beams over the grating surface is not neglegible. To compensate this range difference the grating is used a second time in opposite order. At the end of the receiving package a lens is generating a 8 mm diameter, 3.
Single
parallel
beam
with excellent
optical
quality.
PhotonDetector
To see the full advantage
of the short
photon detector with high accuracy receivers are used in the moment: •
Microchannel
•
Avalanche
laser pulses
is necessary.
and of the errorfree
In the world
of SLR
receiving two types
package of high
a single accuracy
Plates Diodes.
We decided to install a single photon avalanche by the Czech Technical University in our system. •
High ruggedness
under
•
High Quantum
•
Low jitter
•
Low operating
voltage
•
High dynamic
range and
neglectable
•
No additional
electronics
(CFD)
diode (SPAD) (I. Prochazka The reasons for this decision
et al.) were:
developed
field conditions,
Efficiency
(20 %)
(35 ps) (25 V) influence
between
of signal
detector
strength
to the range
measurement
and counter.
!
The housing
for the diode
•
Adjustable
•
Possihlity
•
Protection
•
Flexible
has to meet some demands:
in three dimensions to cool the diode against
humidity
in the pm
below
range.
-10 ° C.
(condensation).
for usage of different
types
of diodes.
The cooling of the diode is necessary because of the high termal noise (some 100 kHz) at room temperature. The temperature of-30°C, which is possible with this setup will decrease the noise far below 100 kHz (Fig. 2) and therefor make the search for satellites at night more easy. To meet •
all this points,
adjustement
we designed
accuracy
a new housing
in each dimension:
12-27
(Fig.
5 - 10pro
3) with the following
specifications:
•
input
beam:
5-10 mm diameter,
•
optics:
•
field of view in our system
•
copling:
•
good
effective
focal length:
to -30°C
mechanical
with stability
parallel
11 mm
(100 pm diode):
peltier under
The housing is made from aluminium, of the diode to the housing is DELRIN.
cooler
and
30 mrad water
field conditions
(5°C) (temperature
the inner moving
part
change,
which
makes
humidity) the
termal
isolation
For the fixing of the diode a very special material with high mechanical stability, high thermal conductivity and good electrical isolation was necessary. To get a thermal equilibrium even at high outside temperatures we decided not only to cool the diode, but the whole fixing plate with powerful peltiers (the hot side of the peltier is water cooled). As some diodes (mainly the diode we use) needs an electrical isolator around it, a material with the mentioned specifications was necessary. In cooperation with the Material Research D,epartement of Hoechst AG, a new ceramic materialAluminium Nitride- was selected. The important properties of this are its high thermal conductivity of 170 W/ink (comparable to pure Aluminium) and its dielectric constant of about 8.5 (good insulator). The powder, together with a sintering aid, are prepared for pressing. The cold isostatic pressed parts, in the form of rough discs, are then turned to improve their finish and a hole is bored in the centre. The binder is then burned out. The samples are sintered at 1840°C for 3 h under a nitrogen atmosphere in a special graphite crucible. After the heat treatment the ceramic parts were finished. They were grond with diamond wheels in all directions to get the high dimensional accuracy and surface smoothness for installation of the measuring diode and for the mounting of the peltier elements. The specifications of the material are given in table 1. Due to the flexibility and the good experience now also used at the new Wettzeli Laser Ranging 3.
with this housing in the last field campaign it is System (WLRS) for the tests of different diodes.
Summary
The new receiving system of MTLRS# 1, consisting of a filter package for field of view, time and spectral filtering and a single photon avalanche diode as detector gives the possibility of SLR with cm accuracy during night and day. The whole system is build very modular and flexible, so easy exchange or usage in other SLR systems is possible. All parts are designed and changes in field an adjustement In the last field campaign
manufactured in a way, is not necessary.
the new receiver
12-28
proved
that
even
to work very
under
reliable
extreme
environmental
and satisfactory.
REFERENCES
P. Sperber, Upgrade,
L. Amberg, 199_.
L. Beyer,
G. Blensid,
U. Hessels,
P. Sperber,
U.
R.
Motz,
W. Beck,
in this
B. Sopko,
S. 219,
Pl_otodlode
I. Prochazka,
Hessels, K.
Kamal,
12-29
R. Motz,
Proceedings, Based
in this
The
Detector
Proceedings,
_ew P*ekage
MTLR5 for
Res_lta
TranJmltting Centimeter
o] the
MTl,
,.qyetem, Sstellite
qstltl
1992.
Ran#iBg,.
@
C_ CO L_ r_
(1) >
U _J ri-
ft _.I l--
r
4_ 0
I--
o_ z
0 _0 _,J
_0 0 C 0 .C 0
O_ LL
12-30
SPAD Dark Count Rate versus Temperature Dark
Count
Rate
[kHz]
1000
3O
Centigrades Fig.
-
Density Termal Specific Flexural Electrical Dielectric
Table
1
2
SPAD Dark Temperature
Count (2.5
Rate versus V above Break)
3,3 glcm 3 170 W/m" K 738 Jlkg K 300 - 400 MPa > 1014 Ohm cm
Conductivity Heat Strength Resistivity Constant
Specification
8,5
of
Aluminium
12-31
Nitride
-
9
tl
'r.-,: , C"
i,.
i r i
'
I t_
_t
_"0 0 -r-I tm
.C 0 C
C 0 0 rO-
C_O C 09
if
.C _a 4-I 0 O% C \
"\
"c
T_I
0 mr-
q
CO
_, =
12-32
0% -H LL
N94-15612 The new MTLRS
Transmitting
System
P. SPERBER, U. HESSELS, R. MOTZ INSTITUT FOR ANGEWANDTE GEOD)_SIE FUNDAMENTALSTATION WETTZELL D-8493 K6TZTING GERMANY W. BEEK, J.W. OFFIERSKI, C. VAN Es DELFT UNIVERSITY OF TECHNOLOGY KOOTWIJK OBSERVATORY FOR SATELLITE GEODESY POSTBOX 581, 7300 AN APELDOORN THE NETHERLANDS
Abstract This paper presents a detailed description about the new transmitting system of the Modular Transportable Laser Ranging Systems MTLRS-1/2. A simplified theory of the Self Filtering Unstable Resonator (SFUR) is explaned. Laser design details are discussed concerning the extreme environmental conditions in which these mobile systems are operating. Details are given concerning the detector are necessary
new avalanche parts in order
START detector. The new SFUR laser and START to bring both mobile systems towards 1 cm ranging
accuracy. 1. Introduction Since
1984
the
two
European
Modular
Transportable
Laser
Ranging
Systems
MTLRS-1,
operated by the Institute for Applied Geodesy (IfAG, Germany), and MTLRS-2, operated by the Delft University of Technology (DUT, The Netherlands), have supplied the international network with laser ranging data from sites in Europe, CIS (former USSR) and North America. To improve the carded out a major upgrade transmitting system also 2. The
ranging accuracy from 5 cm to the 1 cm level, both systems in 1991. The main part of this upgrade was the exchange of the
system consisting of the Laser and upgraded the receiver package [1].
the
Start
Detector
(The
German
MTLRS-1
Laser
The accuracy and the number of returns produced by a satellite laser ranging system is mainly influenced by the duration and energy of the emitted laser pulses. To improve these two points, the original Nd:YAP laser (370 ps FWHM pulse-duration, 10 mJ pulse-energy at 539 nm) was exchanged for a new Nd:YAG laser (30 ps FWHM pulse-duration, 30 mJ pulse-energy at 532 nm). To realize this high demands with a simple and reliable optical configuration, a new resonator setup, the Self Filtering Unstable Resonator (SFUR) [2,3] was used. Together with a simple optical setup, this resonator has the advantage to be less sensitive to optical adjustments and operates minimizing the danger of destroying optical levels. 12-33
with a very components
homogeneous spatial pulse-shape, at high resonator energy output
2.1 Simplified SFUR Theory Fig.
1 shows
the principle
[4]
of the SFUR
M2
resonator.
S.F.U.R.
RESONATOR
aperture
Fth
R2-"
M1 R1
d L
L1
/.2 LO
Fig. Two
mirrors
1
M 1 and M2 are
forming
an instable,
confocal
resonator:
R l + R 2 = 2 "Lo
RI and
R 2 are
the
(concave)
radii
of the
mirrors
and
Lo the
optical'
resonator
length.
This
resonator configuration generates a spot in the resonator, which usually destroys optical elements. If a small pinhole is placed in this focal point this problem disappears and some major advantages can be seen. The diameter d of the aperture has to be chosen in a way, that only the central lobe of the Airy pattern (generated by mirror M2) propagates to M t.
d=
(/2."focal The
length
mode,
Gaussian
of M 2, X: laser
generated
shape,
with
by zero
x/ 2.44
"f
maximum
of
" _.
wavelength)
the
central
intensity
at radius
the
Airy
pattern
has
a smooth,
nearly
ro where
R 1
ro = -
M
• d-
(M
2
= -
--
)
,R2
If the parameters of the resonator are correct, the mode is exactly filling the whole of the active medium. Therefore nearly all the energy stored in the rod is converted laser pulse. configurations.
The outcoupled The aperture
volume into the
pulse-energy is much higher compared to usual resonator (typical diameter d< 1 mm) gives a strong spatial filtering at
12-34
each round trip smoothing the energy distribution in the beam and avoiding exact analysis of the SFUR configuration the influence of the thermal lens in the laser rod has to be taken into account.
hot spots. In an (7"u,: focal length)
Lo = L l +/,2
gl
Rl L0
LI
&=l
g
= 2 "gl
M
(L 1 and
L 2 are
optimum diameter
the
distances
= g
of M1 and
position Lp (distance D of the laser beam
I
-
1
M 2 to the virtual
_
Lp
D
_[g2
-
position
from M_) of the aperture, are given by:
1
d
-
"g2
:
--- 1.5
4.88
.M
1
÷
/?2
• Lp
_/g2
the
-
2 "gl
• _. "(
The laser electronics,
lens).
The
d of the aperture
and
1
1
R'z )
"d" .
Technical
diameter
thermal
"Lo
2
2.2
of the
u
.
--
-i -L"
Realization
system consists of four separate units, the laser an external dye-cooling unit and the control panel.
12-35
head,
the
power
supply
with
A schematicdrawing
of
the
laser
head
is shown
Resonator MI - M2 is folded over a prism PR. acousto-optic modulator AML and a bleachable (PML). The intense 30 ps long pulse is cavity dumped by the pockelscell LASER PC and two polarizers PO. Because of the high energy of the output pulse of a SFUR resonator a single stage amplification (AMPL) is sufficient to get 100 mJ per pulse in the infrared. The second Harmonic Generator SHG converts about 40%
E E
Picosecond dye (Kodak
To
HEAD OPTICAL
place,
the
SFUR
are generated with an in 1,2 Dichloroethane)
CONFIGURATION
I
*
the dust of the - Camera. controlled,
save
pulses 9740
1200
of
POWER
2.
I
0 0
of the energy into green light at 532 nm. The two wavelengths are separated by the dichroic mirror M_. The excessive use of diagnostic diodes and motor driven micrometers allows the fine adjustment laser without opening the cover. Even the spatial shape pulse is monitored by a CCD head is built on a temperature
in Fig.
- MOTOR
mm
MIKES
PCT
- POCKELS CELL TRIGGER
SD
- START
DETECTOR Fig.
For maximum mechanical reinforced invar plate.
SUPPLY
stability,
the
whole
2
laser
CONFIGURATION HIGH
COOUNG
U an < O
ELECTRONICS
VOLTAGE
I I lip08 ,. IIIII ]
[--
]
Fig.
0
.£1_1"1
0
3 3
SMPS
1100
",4
mm
3
Fig. 3 shows an inside picture of the power supply. The power supply and control electronics are also built in an isolated, temperature stabilized housing. The laser switches automatically between 380 V/50 Hz and 460V/60 Hz input, and the 3 phase power consumption is 5 KVA. Two independent control panels for the laser can be used; one for the Cabin, in use during ranging, and another one in the Cart for maintenance purposes.
12-36
Fig. 4 shows the laser temperature built in the Cart which is located
control system. The telescope together with the laser are in full sunshine in the middle of the concrete platform
(Pad). During satellite tracking this Cart is open and TEMPERATURE CONTROL SYSTEM because of extreme environ• BEAM mental conditions (-20°C to +40°C), considerable attention is given to the stability and reliability of the laser (komacel-isolation of the head Ko_,c_ ,so.so. __ _fi, -II and power supply, excellent \ _o_. soPP.v I ..,oo I mechanical stability of all optical components). The heat generated by the flashtubes in \ ELEGTRONIGS _J the secondary cooling system is exchanged to the primary cooling system by means of an internal water to water heat exchanger connected to an external water flow with Fig. 4 temperatures between 5-16°C. The laser was first tested under field conditions during the campaign of MTLRS-I in CIS (Common wealth of lndependant States - the former USSR). The experiences were excellent. /
t ,.,,.cL
The specifications
of the laser are summarized
LASER
in Fig. 5.
SPECIFICATIONS 532 nm 30 mJ 30 ps 20 pps (max) 0.4 mrad
Wavelength Pulse energy Pulse width Rep. rate Divergence Mode locking SHG Beam diameter Environment Power Voltage
active + passive KD*P 7 mm -20 °C to +40 °C 5 kVA 380/4605Nph.
Fig. 5
12-37
3. Start
Detector
To start the time interval counter with high accuracy, the optical output signal of the laser has to be converted with minimum jitter to an electrical pulse, which is used in the start channel of the counter. Until 1990 this problem was solved in the MTLRS in the conventional way: a part .of the green pulse was sent electrical pulse with an amplitude corresponding fluctuating from shot fraction discriminator. this setup To
caused
minimize
to shot. These amplitude Changes in the temporal
errors
these
in the start-channel
errors,
an optically
to a fast photo diode to the energy of the
fluctuations pulse shape
which generates laser pulse which
were compensated and strong energy
an is
by a constant fluctuations in
of the counter. triggered
avalanche
diode
[5,6]
was
the system. This diode delivers an output signal with a constant amplitude the energy of the laser pulse. The output signal is directly used as startsignal a constant fraction generator is superfluous. Furthermore, to introduce high
integrated
into
independent on for the counter, stability and the
possibility to vary the pulse energy during tracking, the start diode is placed before the amplifier (behind mirror M3 in Fig. 2) to detect the infrared light. Fig. 6 shows the output signal of the start diode which has a risetime of 300 - 400 ps and the jitter between optical and electrical pulse is less than 20 ps.
START
DETECTOR
OUTPUT
SIGNAL
+ 7.8 V_
\
_
=.=....._
5 nsidiv
Fig. In order
to get
stable
results
from
the avalanche
start
fibre together with the electronics have to be built ture of the optical bench is stabilized at 25°C.
detector
inside
the
under
laser
6 field
head
where
conditions, the
the
tempera-
4. Summary The upgrade of the transmitting part accuracy of the systems significantly systems worldwide. First tracking' results upgrade
of the receiver
[7] show, package
of MTLRS-1/2 formes and makes them again
that the system's which
is already
12-38
single
the basis to improve the ranging some of the most advanced SLR
shot accuracy
completed
is about
in MTLRS-1.
1 cm
after
the
References: [1]
The new MTLRS-1
Receiving
System,
1992
by P. Sperber,
U. Hessels,
R. Motz,
in
this Proceedings. [2]
Paper 701,
1989
by A. Bianchi,
A. Ferrario,
P.G.
Gobbi,
C. Malvicini,
G.C.
Reali,
SPIE
p. 132.
[3]
Paper WE4.
1987
[4]
Paper 1989 Proce_lings
by K.
Hamal,
V. Hraskova,
H. Jelinkova,
by C. Malvicini, A. Ferrario, G. of the seventh international Workshop
CLEO'85
Proceedings
p.82,
Gabetta, G.P. Banff, G.C. Reali, on Laser Ranging Instrumentation
p. 181. [5]
Paper
1990
Subcentimeter
by I. Prochazka, [6]
Paper 1989 international
[7]
Results
K. Hamal,
Photon
Ranging
All Solid
U. Hessels,
State
Detection
Package,
B. Sopko.
by I. Prochazka, K. Hamal, B. Sopko, Workshop on Laser Ranging Instrumentation
of the MTLRS-1
W. Etling,
Single
Upgrade R. Motz,
by P. Sperber, in this Proceedings.
12-39
Proceedings p. 219.
L. Amberg,
of
L. Beyer,
the
seventh
G. Blenski,
N94-15613 Transputer
Based
Control
System
for MTLRS
E. Vermaat, J.W. Offierski, K.H. Otten, W. Beek, C. van Es Kootwijk Observatory for Satellite Geodesy Delft University of Technology P.O. Box 581 7300 AN APELDOORN THE NETHERLANDS P. Sperber Institut ffir Angewandte Geod_ie Fundamental Station Wettzell 8493 KtTZTING GERMANY Introduction The Modular Transportable Laser Ranging Systems (MTLRS-1 and MTLRS-2) have been designed in the early eighties and have been in operation very successfully since 1984. The original design of the electronic control system was based on the philosophy of parallel processing, but these ideas could at that time only be implemented to a very limited extent. This present system utilizes two MOTOROLA 6800 8-bit processors slaved to a HP A-600 micro-computer. These processors support the telescope tracking system and the data-acquisition/formatting respectively. Nevertheless the overall design still is largely hardware oriented. Because the system is now some nine years old, aging of components increases the risk of malfunctioning and some components or units are outdated and not available anymore. The control system for MTLRS is now being re-designed completely, based on the original philosophy of parallel processing, making use of contemporary advanced electronics and processor technology [Beek, 1989]. The new design aims at the requirements for, Satellite Laser Ranging (SLR) in the nineties, making use of the extensive operational experience obtained with the two transportable systems. Design
goals
Major considerations followed ensure full capability for all modifications and alternative approach. I. Optimize
in the design are to bring down present and future SLR satellites applications through a highly
cost of operations
Deploying SLR systems is quite expensive, design aiming at minimizing these costs, time-between-failure (MTBF) and facilitate a. Minimize
the operational costs, to and to facilitate future structured and modular
crew
in particular in transportable mode. must minimize crew size, increase trouble shooting and repair.
A modern the mean-
size
The default mode of operation will be fully automatic. This means that the system will initiate _d pei'form all basic tasks, e.g. maintaining satellite alert information, ephemeris calculation, initiate and perform calibration and tracking procedures, data screening, Normal Point calculation and data mailing. The routine task for the operator (if any) will be to monitor system performance and to respond to problems. Manual mode of operation is always possible through operator intervention. 12-40
b. Reliability Increasing the MTBF will be primarily accomplished through defining a maximum of all functions in software, running in a multiprocessor parallel architecture. The remaining hardware will be built from high quality, highly integrated components, including Programmable Gate Array (PGA) logic. Integrated components also allow a great deal of miniaturization. c. Self-diagnostics capability Diagnostic tasks running concurrently and localization of problems. Parallel functions.
with the control tasks will enable rapid detection processors are very convenient for hosting these
d. Modular hardware design The hardware is designed with an optimum number of printed circuit (PC) boards. Same processor-functions at different locations use identical PC-boards. Different application-functions are realized with a minimum number of different PC-boards. Interface-functions are accomplished by separate PC-boards in order to optimize hardware portability. Most spares will be available at PC-board level which enables rapid replacement, reducing system down-time under field conditions. II. All-satellite a. Satellite
capability
altitude
This decade a variety of high and low SLR satellites are or will become available. Typical extreme altitudes are ARISTOTELES (200 km) and METEOSAT (geostationary). A design goal is to eliminate any logical restriction to the satellite range in the control system (e.g. by accommodating time interval measurement and event timing). b. Satellite interleaving Because the system will be designed for automatic ranging, the implementation of decision schemes in software for interleaving observations to different satellites will be relatively easy. III. Flexible'design The design of the control system must simplify future modifications in view of new or modified requirements as well as implementation of more advanced technologies. This calls for a highly structured design in software and hardware, which may also enhance the portability of the design to other SLR stations, with different hardware environments. a. Adaptation to modifications Hardware, The general electronic design functions: 1. interfaces, 2. applications and physically separated in PC-boards which are uses PGA logic, which can be easily modified Software The RT-software system is strictly 1. global (functional), 2. device dependent, modifications can be implemented locally in affecting other layers. Because of this high level of structurization SLR systems which are quite different from 12-41
is separated into three major types of 3. processors. These different types are individually exchangeable. The hardware (by software). separated into three independent layers: 3. interface dependent. In this way, the related module at one layer, without
it is feasible to implement this design the MTLRS concept, with a minimum
in of
modifications, primarily in software. b. Expanding processor capability If new requirements dictate additional computer power (e.g. RT-filtering, Frame Grabbing) this capability can be easily implemented in the structured design by adding standard processor boards hosting additional software tasks. To enable implementation of different types of (parallel) processors than the transputer which has been selected in the present design, all software is written in ANSI based high-level languages and no RT-program modifications have to be made because the 3L-compiler [3L] supports different
processors.
c. Highly,manufacturer independent Custom made hardware usually increases the dependence on particular manufacturers. This is avoided by full restriction to standard bought-out components and self-designed PC boards. The parallel p_rocessor set-up eliminates the necessity of selecting a vendor dependent RT operating system and thus ensures the flexibility of adopting any brand of (future) parallel processor. In the current design the INMOS transputer (see below) has been selected because of its early availability and its capabilities. Any future transition to another parallel processor is possible and will basically only require the exchange of the T805 credit card size processor board. Lay-out
of the design
I. Hardware, In SLR the great progress in (opto-)electronics of the last decades has been applied to aspects such as detection, laser technology and timing, but seems to have largely bypassed the issue of Control System design. Here state-of-the-art electronics is introduced in the MTLRS Control System, resulting in a modular design with a high level of reliability,
miniaturization
and flexibility.
Probably the most dominant feature in the design is the application of a parallel processor architecture. This choice supports most of the design goals in a unique way, in particular the issues of modularity and of adaptivity to future requirements for extended computing power. The
INMOS
IM
transputer
I
Parallel-processing nov '88] can be architectures;
computers [BYTE divided into two basic the shared-memory
multiprocessor (fig. 1) and the multicomputer type (fig. 2). All existing microprocessors can be used in the first architecture which will be limited in practice to about 4 processors due so called "von Neumann" bottleneck. Fig 1
to the This
bottleneck arises when one processor to the shared-memory while the other processors have to wait during this time till the "sharedFig 2 memory bus" is free! Only few processors like the INMOS TS00 transputer family ['INMOS 1989] and the Texas Instruments TMS320C40 [TMS User guide] can make an optimal use of the multi-computer architecture because these processors possess high 12-42 reads
or
writes
speed ports
communication ports besides their standard Oinks) the processors communicate with
address and data busses. Through each other in a network where
these each
processor possesses its own memory and thus eliminating the yon Neumann bottleneck. In a practical multicomputer network the number of processors can be almost unlimited. The INMOS transputer family consists of T2.., T4.., T8.. and "1"9... processors supported by link-crossbarswitches and periferal link-adapters. All INMOS processors are equipped with 4 links. Each link consists of one serial transmitting wire and one serial receiving wire both having an unidirectional speed of 20 Mbaud. If a link sends and receives data at the same time, the total data transport will be limited to 23.5 Mbaud/link. The T9000 will be available at the end of 1992 and has a peak performance of 200 MIPS and 25 MFLOPS with link speeds up to 100 Mbaud.
T 805 64 bit Floating
Peak performance 25 MIPS 3.6 MFLOPS
point unit
25 MHz (Internal) Reset "//////t'__ CPU
--
Boot
--
5 MHz clock
from
EPROM
11_7_Etherne --_==_-I
4 Kb SRAM
Memory ....
_
i HAM
I SCSI
2O Mbau_-_d
GPIB
t
¢_
Interface .................
:::::32:::::::::::::::::::::::::::::::
20 Mbaud it=
up to 4 Km ::: ::::::::1
Boot II 4Sbytell RS232/IEEE EPROMI I DRAM I ICENTRONICS Fig 3
For the MTLRS Control System T805 has been selected and
the is
running at an internal clock speed of 25 Mhz giving 25 MIPS and 3.6 MFLOPS peak performance. The external 5 Mhz clock is internally multiplied by 5. Fig. 3 illustrates how the processor can be interfaced to the outside world in a flexible way. The present Control System is designed around a minimum of 5 transputers T805 which are interconnected through their links. A link is connected to a server-program running on a host-PC and through this link all the different programs are distributed through the network and loaded to a particular transputer. Each program is started automatically after it is loaded onto the destination
processor. The design makes no use of the boot-EPROM facility but this makes the processor also very powerful for embedded designs. The word TRAM is an abbreviation for TRAnsputer Module which is an off-theshelf interface board delivered by several manufacturers. For parallel processor networks the software can task can be cutted into pieces which run in parallel can run in two or more processors so that each multitasking in one processor can be programmed
be programmed in various ways; one at different processors, different tasks processor runs a different task. Also in a partly parallel way because the
T805 can perform processes like cpu- operation, link-communication, timing and memoryIO concurrently. This means that while e.g. one task is busy with link-communication, the cpu is free for other tasks, scheduled in a sequential way following task priority. When a task consists of a number of processes, running concurrently in different processors, process-synchronization can be accomplished by the use of channel I/O (inter process data exchange) and semaphores. Part of the internal CASH of 4 Kb SRAM is used to hold all registers for up to 99 different tasks and internal processes. If more than 99 modules are running concurrently, external DRAM is also used to hold registers. In contrast to conventional processors where the cpu has to share time to all processes, the T805 is doing this partly parallel which leads to a much higher performance. 12-43
USER INTERFACE
REAL TIME PC
. MAIN PC [
1,nk
1
]
MAIN CONTROL
lin_
UNIT interface
interface I
I
interface
interface
MOUNT
I/O ]IEEE I IEEE
I II
I
NET
i TIME
1 RS2a__k_2 tlJ :':'.
DATA
ACQUISITION
:::::::
UNIT
interlace
I/O [ IEEE IEEE RS232 _
MAINS
l
ma, lpUtll
POWER
SUPPLY
Mainsflltedng Mainsdisffibutlon S_fetyalarmbutton
Fig 4 12-44
_
timer
_
relays
_
The hardware
lay-out
The hardware system can be separated into four major units, the user interface, the main control unit, the data acquisition unit and the mains power supply (fig. 4). It consists of several printed circuit boards, which largely demonstrate the modularity of the design and make it flexible to future modifications. The basic board is the processor board 1"805. On this creditcard size board the T805 transputer is placed, which is dedicated to parallel processing (see above). In addition this processor board contains 4 MByte memory, a special reset system for checking that the processor is still alive (EMI protection) and four 20 MBaud serial link drivers. Other creditcard size boards in the system are IEEE-488 and RS-232 interfaces for connection to standard devices. These creditcard size boards are daughter boards to the extended eurocard size boards of the Main Control Unit and the Data Acquisition Unit.
MAIN CONTROL
lit
inte[[_ce
IEEE
in
el: ace
MOUNT
J
11 1tJ
RS--
[i!:TsOs:!:i:!:!: I
i:!!:i:!:i:i:i:i:i:i:i?:
8 * RS232 2 * IEEE-488
The
_ce
TIME
I/0
fig
er
UNIT
Clock Synchronization Timer Range Gate Window
2 - axis mount controller limit-& safety switches
Computation network
5
Main I)
Control
the I/0
Unit (fig. 5) is made
board
for connecting
up of four extended
the processor
to IEEE,
eurocard RS-232
size
boards:
devices.
2) the TIME board for all time dependent tasks: 4 channel event counter (low accuracy 20 ns), range gate programmable generator (400 ps one shot accuracy), window programmable generator (20 ns resolution), The
programmable generator/synchronizer for the shutter, independent from window, RT-clock with battery backup, programmable synchronization for all required signals (e.g. laser firing). TIME
board
requires
10 Mhz and 12-45
1 pps input signals.
3)
the MOUNT board for driving a 2-axis telescope. The specifications for both axes are: 32 bit position and 16 bit velocity and acceleration controlling, three 16 bit coefficient programming for PID filter, DC and DC-Brushless motors driving, position and velocity mode of operation, interface for quadrature incremental encoder with index pulse, absolute encoder up to 32 bit, limit-, safety switches, etc. ports, joystick connection, nonvolatile RAM for storing position, offset, etc. during power off, without battery backup.
4)
the NET board with a minimum of one processor board with extending computer power up to five processor boards. Additional be implemented for expanding the network even further.
Instead of one big backplane interface, four individual backplane designed. The design of each small backplane is dedicated to application, e.g. dependent on the type of encoders etc. Each backplane can easily be modified to different input signal positive, NIM, "VI'L, 50 fl, ....
DATA
ACQUISITION
the possibility NET boards
of can
interface boards are the typical hardware levels
e.g.
negative,
UNIT
interface
lie IEEE IEEE RS232 RS232 T805!:!:!:!:!:!:. -
2"777
DAC' s
inputs _
ADC's
outputs
i/// i/// r/// _-///
_-//J LL/-Z
opto counter / _..._.... couplers timer _///_ relays
':';':-:-;-:-:-:-:-:-:-2;!
8 ° RS232 2 * IEEE-488 Remote Control On/off, Standby Temp. control etc.
Fig 6
The Data Acquisition Unit (fig. 6) will be used for controlling additional hardware for the purpose of automation e.g. DC-motors, stepper-motors, temperature control, contacts checking and on/off-switching of equipment. It consists of an I/O extended eurocard size board which is identical to the one in the main control unit, together with several Data 12-46
Acquisition -
boards like:
12 bit D/A-converter offset. 12 bit A/D-converter and auto-calibration.
(multiplexed (multiplexed
for for
8 outputs) 8 inputs)
with with
programmable
programmable
range range,
and offset
24 parallel input/output ports. Counter/timer for controlling counting/timing functions. Galvanic separation by opto-couplers and solid state relays.
The User Interface (fig. 4) consists of two identical 486 Personal Computers (PC) which are linked to the transputer network by means of 20 Mbaud link extension boards located in each PC. At this level the system can also be connected to Local and Wide Area Networks protocols. Finally filtering
by
adding
standard
interface
boards
to
the
the Mains Power Supply (fig. 4) is designed mains. It also features an alarm button for safety.
PC-ISA
for
bus,
distribution,
utilizing
standard
switching
and
II. Software General aspects The computer configuration includes a transputer network and two identical PC486AT's, the Main PC and the Real-Time PC, each connected to the transputer network by a so called 'link'(fig. 4). On both PC's the operating system MS-DOS is running together with the highly efficient and friendly Microsoft WINDOWS which is a widely accepted industry standard graphical environment for PC's. In the transputer network the RT-software is running without any operating system. On both PC's the WINDOWS TRANSPUTER FILE SERVER is running. The Main PC hosts the offline _oftware and is used for data storage. Tasks like: site installation, preparing predictions, real time processes, data screening, normal point calculations and data mailing are initiated from or performed by the Main PC. The Real-Time PC interacts with the ranging process as a terminal through the on-line Real-Time (RT) windows transputer file server program, supporting graphics capabilities for the transputer network during all real time processes like: satellite ranging, target calibration, telescope alignment and diagnostics. Through the Real-Time PC the operator interacts with all ranging related processes. The transputer network is built around several transputers where the actual RT-software is running in order to directly control the hardware. Modification of (default) input parameters for the various modules by the operator is based on WINDOWS dialogue boxes and menus which are on both PC's supported by extensive help information. In case of malfunctioning of one of the PC's, the software is designed to run on one PC only, with minimum inconvenience to the operator. The
Thus
each PC is a back-up
unit for the other
one.
off-line software This software is largely based on the original MTLRS system and will be updated for compatibility with the PC-hardware platform under MS-DOS. The software will be embedded in the WINDOWS graphical environment. Error handling is supported by supplying whenever whereas
help information feasible. Primarily individual existing
programmes. Both standard to ensure
and by allowing the new software modules are kept
operator intervention in run-time package has been re-written in C, in FORTRAN-77, callable from C-
the C- and the FORTRAN coding are based on to the ANSImaximum portability of the software. All data files have been 12-47
defined format.
in ASCII-format,
unless
specific
requirements
dictated
the
use
of a binary
The RT-software The transputer software system consists of a set of communicating processes, logically combined in functions. To make the software usable for other ranging systems and to facilitate future developments, the software has been structured into three layers: a. b. c.
the GLOBAL, SLR SYSTEM independent software the DEVICE or data format dependent DRIVER software the INTERFACE type dependent DRIVER software
Diagnostic capabilities are integrated in all three running concurrently by default or can be activated
layers of the RT-software to run concurrently.
and
are
a. Global system The global system includes all functions of the present MTLRS RT-software. The current MTLRS limitations concerning the observation range, the correction domain and the fixed firing epoch have been eliminated. Interleaving satellite ranging is made possib!e. To optimize this, the coarse pass prediction integration and the fine prediction interpolation are moved into the RT-software, This also allows firing epoch dependent range residual calculation to speed up data filtering. The meteo data and the UTC-GPS time are made available to the RT-time system. b. Device
driver
A device driver prepares the standard information from the global system to meet the requirements of the device and vice versa_ It executes a device function by preparing a device command according to the operational device protocol and by calling interface drivers for data transfer. Device drivers are available for all external devices to be accessed c. Interface
by the global
software.
driver
An interface interface'to
driver transfers the data from the transputer network through each device and vice versa. No modifications are applied
a hardware to the data.
Interface drivers are available for each type of interface and protocol used by the external devices. Event interrupt processing is supported for devices which are capable of asserting the transputer event signal. International
design
standard
Because of the structured approach this activity will contribute to the control systems.
to the design establishment
of this control system it is hoped that of an international standard for SLR
References -
Beek,
W. International OCA/CERGA,
and K.H. Otten, "MTLRS-2 Workshop On Laser Ranging Grasse, France.
Upgrade", Proceedings Instrumentation, Matera,
Seventh 1989,
INMOS, "The Transputer Databook", Second Edition, document No.72 TRN 01, 1989, Redwood Burn Ltd, Trowbridge. TMS User guide, Texas Instruments Data Book: TMS320C40 User guide. BYTE: November 1988, Parallel Processing in depth, TS00 and counting. 3L Ltd. 'Peel House, Ladywell, Livingston EH54 6AG SCOTLAND, Telefax: -506-415944. 12-48
203
UK
Airborne
and Spaceborne Systems
N94-15614 AIRBORNE
2 COLOR
RANGING
EXPERIMENT
Pamela S. Millar James B. Abshire Jan F. McGarry÷ Thomas W. Zagwodzki* Linda K. Pacini*
Experimental Instrumentation Branch, Code 924 NASMGoddard Space Flight Center Greenbelt, Maryland 20771 +Crustal Dynamics Project, Code 901 *Photonics Branch, Code 715
ABSTRACT Horizontal
variations
in the atmospheric
refractivity
are a limiting
error source for many
precise laser and radio space geodetic techniques t-7. This experiment was designed to directly measure horizontal variations in atmospheric refractivity, for the first time, by using 2 color laser ranging_me_urements to an air_craf_t_. The^2.collor!a_r syste_k2t_e a T-39 aircraft. Circular patterns wmcn extenaeo irom mv _,u _, D.C. Beltway to the southern edge of Baltimore, MD were flown counter clockwise around Greenbelt, MD. Successful acquisition, tracking and ranging for 21 circular paths were achieved on three flights in August 1992, resulting in over 20,000 two color ranging measurements.
INTRODUCTION Atmospheric refractivity is a limiting error source in precise satellite laser ranging (SLR). Several models have been developed to correct SLR measurements for the increased optical path length caused by atmospheric refractionl-3'8: 9. The first three fomr_Ul_c_S_et_ at atmospheric refraction is spherically symmetric, ano require surtace metero oga laser ranging site. A higher order model developed by Gardner 8,9 can, in principle compensate for spatially varying atmospheric refraction by utilizing pressure and temperature measurements at many locations near the laser ranging site. However, this model depends on the surface measurements being strongly correlated to atmospheric density at higher altitudes. 13-1
A more accurate method for determining the atmospheric correction is to directly measure the atmospheric dispersion with a two color laser ranging system4-7. In the two color ranging approach, the single color range and the differential delay between the two colors is measured. Due to atmospheric dispersion, the differential delay is proportional to the pathintegrated atmospheric density, and therefore it can be used to estimate the atmospheric correction. In 1980, Abshire proposed to measure the magnitude of the horizontal gradients in atmospheric refraction by making dual color ranging measurements to an aircraft equipped with a retroreflector. We have developed and successfully carried out such an airborne two color ranging experiment. We expect that data from this experiment will improve our knowledge of gradients in the refractivity, and could contribute towards improving atmospheric models.
APPROACH
Our experiment utilized Goddard's 2 color ranging system at the 1.2 meter (m) telescope facility with a cooperative aser target package on a T-39 aircraft. A simplified diagram of the experiment is shown in Figure 1. The ground-based laser system tracked and ranged to the aircraft as it circled Greenbelt, MD. With this circular flight pattern, the aircraft passed partially over two major cities, Washington D.C. and Baltimore, and land near the Chesapeake bay. It is likely that variations in the terrain temperatures will cause horizontal gradients in the air density directly above, which could be measured by the experiment. The initial step in the experiment is to acquire the aircraft's approximate location. A realtime GPS data relay link was developed for this purpose. A GPS receiver on the T-39 relayed the aircraft position every 3 seconds through an RF digital packet link to the ground telescope. The telescope's tracking program then determined the pointing angles to the aircraft by extrapolating the aircraft's position from the GPS data. Once acquired, we closed an automatic tracking loop by using a CCD camera and frame grabber which commanded the 1.2 m telescope to automatically track the aircraft's 810 nm laser diode beacon. The aircraft target package was manually pointed to the ground from inside the aircraft by viewing the ground beacon which was modulated at 5 Hz. To determine the optical path length we measured the range 20 psec resolution laser ranging system. For the differential streak camera-based receiver which recorded the reflected 1.2 nanosecond (nsec) time window.
AIRCRAFT
to the aircraft at 355 nm with a delay measurement, we used a 355 & 532 nm pulses within a
INSTRUMENTATION
Figure 2 shows the T-39 aircraft based at (Wallops Flight Faciiity) _ in this experiment, along with the flight crew. The T-39 is a two engine, 4 passenger, jet aircraft capable of maintaining 12 kilometer (km) altitude. The three science flights were limited to 6 - 7 km altitudes due to high cirrus clouds near 7 km. The target package was located beneath the nadir port of the aircraft just aft of the air brake. On the aircraft we used a combination of laser and electro-optic instrumentation for pointing the target package with two radio transceivers for data and voice communications to the ground laser facility. A photograph of the target configuration is shown in Figure 3. The target package consisted of a cube comer array (CCA), a laser diode beacon and a CCD camera with a narrow bandpass filter. The package was secured to a commercial pan and 13-2
tilt camera mount and was controlled with a joystick inside the aircraft. The entire package was protected by an aluminum enclosure which incorporated a 1/4" thick quartz window to transmit the optical signals at 355, 532 and 810 nm. This window was tilted -3 °, with respect to the aircraft nadir, so that the beams would transmit through at right angles to the window. We used baffles on both the laser diode beacon and the CCD camera to reduce scattering of the laser beacon close to the enclosure window. Table 1.
from the window The target package
into the camera. The baffles extended components and parameters are listed in
We used several techniques to control the target package's temperature. To avoid condensation on optical surfaces, tape heaters were attached to the inner walls of the CCA housing and around the filter adaptor tube on the CCD camera. Resistive heaters were installed on the back mounting plate of the target package. An AD590 temperature sensor was placed on the filter adapter of the CCD camera. The sensor indicated that at 7 km altitude the target package stayed at 10°C for the flight duration. Dry nitrogen was flushed into the target enclosure before takeoff and during ascent, descent and landing to displace water vapor, which could condense on cold optical surfaces. The target package could be pointed in azimuth :£5 ° from port, parallel to the left wing and in elevation +5 ° to -15 ° from horizontal. The operator who moved the target package via joystick could instruct the pilots to adjust aircraft attitude if the ground beacon was moving outside of the CCD camera's i0 ° field of view (FOV). This was necessary particularly in azimuth during flights with strong cross winds. The flight crew consisted of two pilots and two science team members. One person pointed the target and communicated with the pilots, while the other operated the GPS control software and maintained radio communication with the ground ranging site. The GPS receiver was used to receive the aircraft's lattitude, longitude, altitude and time. The GPS receiver relayed its information to the flight computer via a RS232 port, as well as to the packet radio. The packet information was transmitted in bursts every 3 seconds. The flight computer allowed the operator to verify that at least four satellites were in the receivers FOV and that the GPS data being sent was correct. An aircraft LORAN unit was used as a backup to initialize the GPS receiver in the event of a computer crash. The ground packet radio receiver relayed the aircraft's position to the DEC PDP 11/24 computer. This mount control computer pointed the 1.2 m telescope to the aircraft. While flying the circular pattern, the pilots used a TACAN transceiver which gave them slant range to GORF where another TACAN transceiver was located.
GROUND-BASED
RANGING
& TRACKING
INSTRUMENTATION
The airborne two color laser ranging experiment was one of several projects which have used Goddard's 1.2 m telescope ranging & tracking facility. This facility was developed for satellite laser ranging. We tried to design the aircraft experiment to minimize the impact to the ongoing satellite ranging program, so that only slight system modifications were made to convert from satellite mode to aircraft mode. A simplified block diagram of the system is shown in Figure 4, with system parameters given in Table 2. For the aircraft experiments the Nd:YAG laser was operated at 10 mJ at 355 nm and 0.3 mJ at 532 nm to avoid damaging the telescope optics. The laser was housed about 10 meters from the base of the telescope. Figure 5 shows the laser transmitter and two color optics. The experimenters area is located at the base of the telescope near the telescope focal plane. This area contains the range receiver electronics, aft optics and streak camera. The aft optics 13-3
for the aircraft configuration is shown in Figure 6. The laser output is directed hole in the 45 ° bifurcated mirror through the telescope and to the aircraft.
through
a
The ranging operation can be described by referring to Figure 4. A start diode samples the outgoing laser pulse to initiate the time interval measurement sequence. The aircraft return pulses are then reflected at the 45 ° birfurcated mirror and into the aft optics receiver. In the receiver a small percentage of the return is split and detected by the MCP photomultiplier tube. This generates the stop signal for the time-of-flight measurement as well as the pretrigger for the streak camera. The majority of the received signal was then separated into 532 nm and 355 nm paths by a dichroic mirror and bandpass filters. Each color was focussed into a fiber optic delay line. The optical delay was required to allow pre-triggering the streak camera with respect to the optical pulse's arrival time. The delay fiber bundle was composed of 27 fused silica fibers with 100 i.tm core for each color which were round at the input side and formed into a single row at the output side. The signals were then imaged onto the streak camera photocathode by the streak camera's input lens. The streak camera's 1.2 ns sweep speed setting was calibrated and used to achieve -4 psec/pixel resolution. During pre-flight tests the detection threshold for optical pulses transmitted through the fiber optic cable to the streak camera was measured to be 6,600 photoelectrons at 355 nm and 4,200 photoelectrons at 532 nm. At the transmitter, an optical delay was added to the 532 nm pulses to allow both 532 and 355 nm received pulses to be recorded within the 1.2 ns sweep window. The 532 nm pulse was delayed with respect to the 355 nm pulse by using a total internal reflection (TIR) cube corner mounted on a computer controlled linear motor stage. This time offset was used to compensate for the additional -2.7 nsec round trip atmospheric delay at 355 nm. Each streak camera waveform pair was digitized to 256 time pixels by 8 bits amplitude and was recorded on hard disk. The streak camera waveforms were stored on the PDP LSI 11/23 at a 2 Hz rate. Each file consisted of the optical waveform pair, the 355 nm time-offlight measurement, the transmitter 532 nm delay setting, telescope azimuth and elevation angles, and, other relevant tracking information. The aircraft was acquired by using the GPS measured aircraft positions which were relayed to the tracking computer. Every 20 msec, the computer tracking program extrapolated the aircraft's pre_ent angular position from the three most recent GPS data points and directed the mount to that angular location. GPS tracking was usually sufficiently accurate to keep the aircraft position within the CCD camera's -.0.3 ° FOV. The tracking loop was closed by reading an X-Y digitizer which determined the angular offset of the aircraft's 810 nm laser diode beacon within the COD FOV. In this mode the mount was driven so that the beacon's angular position stayed within the center of the CCD FOV. Optical background from bright stars, the moon and other aircraft were suppressed with a 5 nm FWHM bandpass tilter in front of the tracking camera. The telescope was able to track the aircraft to a precision of-200 microradians, and successfully tracked the aircraft across the face of a full moon.
STREAK
CAMERA
CALIBRATION
When making two color ranging measurements at 532 and 355 nm, the differential delay is -1/12 the 532 nm delay. The differential delay must be measured to better than 5 psec for i cm single calibrated
color corrections 10,11. to permit this accuracy.
The
streak
13-4
camera's
sweep
speed
had to be carefully
The first stepinvolved finding the zerodelaysettingin thetransmitter.A cubecomerwas placed in the optical pathin front of thetelescopeto avoid anyatmosphericeffects. Then the transmitter's532nm delaywasadjustedto a positionwherethe 532and355nm pulses arrived atthe streakcamerasimultaneously.This wasdenotedthezeroreferenceposition. Next anoptical delayof 100picosecondswassetat the transmitter.Eachwaveformpair was smoothedandpeakpositionswerecomputedalongwith the differencebetweenthe peaks.The 100 psecoptical delay setting was then divided by the peak difference (in pixels) to yield aninversevelocity measurement.This dt/dx value (psec/pixel)wasthen plottedat thex positionwhich wasatthe midpointof the two peaks. This processwasrepeatedseveralhundredtimesasthe pulsepairsweremovedacrossthe streakcamerawindow. Thecoefficientsfor the sweepspeedwerecomputedasthe bestfit to the inverse velocity versus midpoint plot as shown in Figure 7. To check the calibration, and to process the flight data, the time difference between the 355 and 532 nm pulses were computed by integrating the inverse velocity profile 5. The calibration was checked by displacing the TIR cube comer to other known values for comparison with calculated optical delays. The system's calibration was tested either before or after each aircraft experiment, and agreement was typically -4 psec.
SUMMARY: On the evenings of August 5, 6 and 7, 1992 we conducted a two color ranging experiment to an aircraft: Each ranging experiment lasted about 2.5 hours as the aircraft circled the ranging system at an altitude of 6 to 7 km and a slant range of 20 to 25 km. This resulted in 7 to 8 full rotations around the ranging site per flight. About 6,000 to 8,000 two color laser ranging measurements were recorded on each flight. In total 30 Mbytes of calibrated 2 color ranging data were collected. An example of a waveform pair from 8/05/92 is illustrated in Figure 8. Both smoothed and raw data for the green and UV are shown. The waveforms are smoothed for analysis by convolving with a raised cosine pulse. Most of the waveforms had pulse widths wider than the transmitter. Some pulse broadening was caused by modal dispersion in the multimode fiber delay lines. Additional broadening on some signals may be due to saturation of the streak camera. However, in most cases, the sharp leading edges of the optical pulses were preserved in the waveforms. Our work to date shows that timing to the pulse's leading edges appears to have the least timing jitter. I
We are currently in the process of normalizing the data for varied range and elevation angle as well as optimizing our method for calculating the differential delay between the 2 color pulses. These results will be compared to atmospheric models3,8, 9 and published upon completion. ACKNOWLEDGEMENTS The authors wish to thank NASA Headquarters Code SEP, the Crustal Dynamics Project and the EOS GLRS instrument project for supporting this work. We are indebted to Amie Abbott, Jonathan Rail, Richard Chabot, Jack Cheek, Kent Christian, Jimmie Fitzgerald, Dan Hopf, Bill Krabill, Earl Frederick, John Riley, Robert Gidge, George Postell, Virgil Rabine, Dave Pierce, Evan Webb and John Degnan for their many contributions towards the completion of this project.
13-5
REFERENCES 1. Bender,P. L. and J. C. Owens,"Correctionof Optical DistanceMeasurementsfor the FluctuatingAtmosphericIndexof Refraction," J. Geophys.Res.,70(10) pp. 2461-2462,May 1965. 2. Marini, J. W.,
and C. W. Murray, Jr., "Corrections Atmospheric Refractions at Elevations above Nov. 1973.
.
Herring; T. A., "Marini and Murray Atmospheric Range Correction to the CSTG SLR Subcommission meeting NASACDP Principal meeting, Munich, October 1988.
4. Abshire, J. B., "Plan for Investigation Systems," NASA X-723-80-10, .
6.
o
of Laser Range Tracking Data for 10 Degrees," NASA X-591-73-351,
Atmospheric Errors January 1980.
Abshire, J. B., and C. S. Gardner, "Atmospheric Laser Ranging," IEEE Trans Geoscience 425, 1985.
in Satellite
Formula," Report Investigators
Laser
Ranging
Refractivity Corrections in Satellite & Remote Sensing, GE-23(4) pp. 414-
Degnan, J., J., "Satellite Laser Ranging: Current Status Trans. Geoscience & Remote Sensing GE-23(4)pp.
and Future 398-413,
Prospects," 1985.
IEEE
Bender, P. L., "Atmospheric Refraction and Satellite Laser Ranging," submitted to: Syrup. on Refraction of Transatmospheric Signals in Geodesy: The Hague, May 19-22, 1992.
8.
Gardner, C, S., and B. E. Hendrickson, "Correction of Laser Tracking Data Effects of Horizontal Refractivity Gradients," Radio Research Ld_ratory University of Illinois, Urbana Illinois, December 1976.
9.
Gardner, C. S., "Correction Refractivity Gradients,"
for the 478,
of Laser Tracking Data for the Effects of Horizontal Appl. Optics 16(9) pp. 2427-2432, September 1977.
10. Im, K. E., C. S. Gardner, J. B. Abshire, and J. F. McGarry, "Experimental evaluation of the performance of pulsed two-color laser-ranging systems," Soc. Am. A 4(5) pp. 820-833, 1987.
J. Opt.
11. Zagwodzld, T. W., J. F. McGarry, A. Abbot, J. W. Cheek, R. S. Chabot, J. D. Fitzgerald and D. A. Grolemund, "Streak Camera Returns from the Relay Mirror Experiment (RME) Satellite at Goddard space Flight Center's 1.2m Telescope Facility," submitted to: American Geophysical Union Monograph, Space and Geodesy and Geodynamics, Fall 1992.
13-6
Table1. 1.CubeComerArray
2. Laser
Diode
Target
Beacon
AircraftInstrumentationParameters 23 element array, 2.5 cm cube comers, 5 arc second accuracy, UV coated, R=78% @355 rim. SDL-2460 A1GaAs Array, 780 mW at 810 nm, 7 ° azimuth by 8 ° elevation divergence.
3. CCD Camera
Philips model 56471 camera, 25 mm lens, f/0.7, 10 ° FOV, Bandpass Filter: 810 + 2.5 nm.
4. Pan & Tilt Camera
Mount
5. GPS Receiver
VICON model V353AtrI'V variable drive system and tilt controller, 8" by 12.75" mounting plate Motorola EagleVIII, 4-channel, simultaneous L1 C/A code carder
O
O
07 O6
oo oo @ o°o oOO o_ooo_ _ oo c_
o °
05 O4 O3
0
0
O_
02 01 00
0
I
I
22
t
I
,
44 Streak
Figure
7.
I
I
66 Camera
I
_
88
1
110
Window
z
I
132 Location,
t
i1
I
154
I
176
L
t
198
X (pixels)
Streak camera sweep speed calibration for 2nsec sweep using data taken 3/24/92. The linear fit using 100 data points is displayed in the upper right hand corner of the plot. The units of inverse velocity are psec/pixel.
13-15
FLIGHT 260
I
I
DATE I
I
8/05/9Z I
I
'
,"
I
I" '"
i
!
240 220 200
1BO
,6e X
_' 14o
I-
,-,
100
_.1 O.
=: _C
BO 60 40 20 0
I
!
0
20
40
_
60
I
,
i
GREEN 260
--T
_----
F'-----I ---_
I
,
1
•
I
i
100
BO
i
I
!
I
120
140
160
1B0
i
200
I
220
=
I
i
240
250
WAVE POSITION[P]XELS] ]
1
_
I
,
1
_
I
,
i
.
i
I
i
240 220 20ff 180 O3 --I
"' x
160
_'14o 120 I,-
'--' 100 _I
.,_ BO 60 40 20 =
0 0
i
i
40
20
Figure
8.
60
,
80
100 120 t 40 160 U-V ',/AVE POSIT[ON [P]×EL5]
100
I
200
=
I
220
_
240
Two color waveform pair recorded by Hammamatsu model C1370 Streak Camera. Each waveform is shown in both raw and smoothed form. The horizontal scale factor is about 4.2 ps/pixel determined by calibration. For this pulse pair, the differential delay (including the optical delay set in the 532 nm path) was 2.667 nsec. 13-16
'60
N94-15615 GLRS- R 2-COLOUR
RETROREFLECTOR TARGET PREDICTED PERFORMANCE
Glenn
DESIGN
AND
LUND
Optical
Department
AEROSPATIALE100 Boulevard 06322
Space
& Defense
Division
du Midi
CANNES
LA BOCCA
FRANCE
ABSTRACT
This paper reports on for the GLRS_R spaceborne
the retroreflector dual-wavelength
ground-target laser ranging
design system.
The described passive design flows down from the requirements of high station autonomy, high global FOV (up to 60 ° zenith angle), little or no multiple pulse returns, and adequate optical crosssection for most ranging geometries. The proposed solution makes use of 5 hollow cube-corner retroreflectors of which one points to the zenith and the remaining four are inclined from the vertical at uniform azimuthal spacings. The
need
for
fairly
(within turbulence diffraction lobes, vectorial accuracy compromise solution of the retroreflector
large
(~
I0
cm)
retroreflectors
is
expected
limitations) to generate quite narrow thus placing non-trivial requirements on the of velocity aberration corrections. A good is found by appropriately spoiling just one dihedral angles from 90 ° , thus generating
two symmetrically oriented The required spoil angles ground target latitude.
diffraction are found
to
lobes have
in the return little dependance
Various link budget analyses are presented, influence of such factors as point-ahead turbulence, ranging angle, atmospheric visibility target thermal deformations.
13-17
beam. on
showing the optimisation, and ground-
i.
BASIC
GROUND
TARGET
REQUIREMENTS
During the various study phases investigated of the GLRS project, the Ground Target established to be of most significant following
:
• Choice
of
a
multiple-retroreflector,
• As nearly full zenith angles • Avoidance
of
ambiguous
• Adequate photon under most clear • Moderate
cost
high
of of
2.
following and as a
BASELINE
The
space practical
local
in
keeping
ranging
with
the
accuracies
GT
design leads to the choice (RR) concept where full summation of several contributing
approach diagram
the gradual fall-off inter-RR crosstalk
TARGET
of
of a sky RR
result firstly a static RR,
of this diagram (i.e. multiple
achieve requirements be achieved
an
-
from and from pulse
acceptable and the need under most
Although
applications)
GT
in
between of RRs. i00 mm, minimise
good with size
is is
CONCEPT
5-retroreflector
limits
to
returns.
sub-centimetric conditions.
in this energy
provides a good compromise overlap and minimal number have a useful diameter of construction in order to deformations.
up
concept.
sections the proposed GLRS-R GT design its numerically simulated performance function of several important system variables.
GLRS-R
baseline
possible,
pulse
The adopted solution must therefore compromise between somewhat conflicting for accurate range measurements to conditions. In the described, illustrated
target
reliability.
difficulties reflec[ed
secondly - because the requirement return) avoidance.
as
correction,
budget for atmospheric
and
sky
(multiple)
The requirement of a passive multiple fixed Retroreflector coverage is achieved by the FOVs. inherent non-uniform
passive
coverage of the of at least 60 ° .
• Adequate velocity aberration link budget requirements.
The the
during the course (GT) requirements importance were the
thermal small
and
design
performance solid
temperature
13-18
illustrated
in
Fig.
1
full sky coverage, minimal FOV The individual retroreflectors and will need to be of hollow thermally induced wavefront cube-corners, excursion
is
achieved there beyond
(in are which
the resulting re fract iv_._-ind'ex unacceptable wavefront distortions.
gradients
will
generate
SOUTtt
Figure
1.
Proposed
baseline
As shown in 9 10p, wavefront distortions
5-
cube
corner
ground-target
thermo-mechanical effects in hollow retroreflectors,
can
also although
are expected to be an order of magnitude smaller induced under comparable conditions in a refractive reasons of resistance to environmental influences, reflectors will need to be covered by a protective quality)
lead
to they
than those medium. For the hollow (optical
window.
Preliminary thermo-mechanical analysis has shown that the GT support structure can be made of common materials which would give rise to reflector location stabilities of ~ 3 mm, for temperature excursions of ± 50 ° C (± 90 ° F). If required, partial correction for these excursions could probably be made using epoch and climatic data together with an appropriate thermomechanical model for support structure deformations.
13-19
As explained in §3 and §4, velocity aberration achieved by designing the RR far-field diffraction exhibit a symmetrical twin-lobe structure. Each be oriented (about its local with respect to the overhead achieve appropriate alignment
correction patterns
of particular tracks, lobes.
normal) in a spacecraft of the reflected
the in
is to
RRS must direction order to
Although a 45 ° inclination of the peripheral reflectors provides good overall FOV coverage and has been assumed in the following analyses, the choice of this value is somewhat arbitrary. Parametric analysis could reveal a more favourable inclination, depending on the criteria used to trade link budget performance at high zenith-angles against FOV overlap limitations. Variants involving more than 4 peripheral reflectors could also be considered, although they would incur an increase in the extent of
FOV
overlap,
It is inhibit crosstalk
assumed operation effects
any allowed the return relates the
3.
and
higher
INFLUENCES
Two-way
IN
atmospheric
conditions,
mean
zenith
long-exposure
•
dihedral
• Detection use
of
camera.
and
will where for
angle
receiving
PERFORMANCE
depending
and
GT
energy
depending
influences Those which are listed
on
visibility
altitude.
characterised
by (
}
Cn2
local and on
wavelength
and
the
(h).dh).
zenith range.
ranging
angle,
local
geometry
and
velocity.
characteristics
techniques, a
BUDGET
as determined by satellite azimuth
aberration, height
Retroreflector and
angle
turbulent
• Ranging geometry, RR incidence angle,
satellite
ranging strategy of geometries and determines,
several quite different link budget performance. to in the "present paper
turbulence,
• Velocity
LINK
transmission,
local
• Atmospheric
costs.
operation, which of the RRs must be providing An appropriate deterministic correction then RR range to a common GT reference point.
AS shown in Fig.2, there which can affect the system are considered or referred below : •
GT
that the spacecraft (S/C) for the small percentage are expected to be strong
ranging signal. measured
PRINCIPAL
overall
such
as
the
case
size,
optical
quality
spoiling. which telescope,
in
transfer
of
GLRS-R
optics
and
imply a
the
streak
I SPACI_ORNE
_ACEBORNE
El_ SSION
-. _,
+ Wavebngths + Lasere_ergy &Pdsewid_h + Be_mPointing& Divergence
| J
6.5"1010 surface elevation measurements with the selected horizontal resolution (grid size) and an image of Earth's surface reflectance at 1 _m wavelength with a similar level of detail. These products will be developed with minimal ground processing, stored on compact optical disks, and made available to the scientific community in a timely fashion. Analysis and use of the topographic data will be done by tl_e end user in the scientific community. REFERENCE: Gardner, C.S., "Generalized Applied Optics, 1992.
Target
Signature
Analysis
for Laser Altimeters",
ACKNOWLEDGMENTS: The definition of the MBLA instrument was made possible through the efforts of a number of individuals in the Laboratory for Terrestrial Physics (LTP) at the Goddard Space Flight Center and' in the aerospace industry. Notable among these efforts were those of David Rabine in the University Research Foundation of the Maryland Advanced Development Laboratory, Nita Walsh of Science Systems and Applications, Inc., Ying Hsu of the Optical Corporation of America, David Thompson of Spectrum Astro, Inc., and Tom Baer, Spectra Physics, Inc.
13-81
MULTI-BEAM LASER ALTIMETER MISSION CONCEPT
EARTH PROBE SPACECRAFT SUNLIGHT 400 km SUN-SYNCHRONOUS 6am/6pm POLAR ORBIT
LASER
PULSES
(30)
1 _m WAVELENGTH
SENSOR FOOTPRINT 30 m diam.
NADIR TRACK
ACROSS TRACK DIRECTION
9OO m SWATH WIDTH
Fig.
13-82
1
1.1_
v
(_
E oi
F=
n=
0 t-_r:r_'_ =t
m
(_
o a= n,' w )== w
) ( (
_.o
I
-b °_
==J
t--
8_
n,= W
i
=J
E_
_=
13-83
13-84
i
_J
g
13-85
LO U-
nW W m
-J
] q)
W rn .J
13-86
E o
Poster Presentations
N94-156 1 SATELLITE
M (_ech, Faculty
of Nuclear
phone
/ fax
K.Hamal,
Science Brehova
+42
LASER STATION STATUS 1992
H.Jelfnkov_l,
HELWAN
A.Novotn)_,
I.Proch_ka
and Physical Engineering, Czech Technical 7, 115 19 Prague 1, Czechoslovakia
2 848840,
telex
B.B.Baghos,
121254
Y. Helali,
fjfi c, E-mail
University
[email protected]
M.J.Tawadros
National Research Institute of Astronomy and Geophysics, Helwan, Egypt phone / fax +20 2 782683, telex 93070 hiag un, E-mail
[email protected]
GENERAL
The Institute
Satellite
of Astronomy
Laser and
Station
Helwan
Geophysics
has been
in Helwan,
ope'r.ated jointly Egypt
and the
by the Czech
National
Technical
Research University
in Prague, Czechoslovakia (see Proceedings of the 7th International Workshop on Laser Ranging Instrumentation, Matera, 1989). The station components have been carefully tuned to increase the system overall stability and reliability critical for the remote location. The mount correction model based blind satellite implemented, 1 satellite
has
on the Gaussian smoothing (Kabel:_, 1990) has been implemented to simplify the acquisition and tracking. The on-site normal points generation algorithm has been the station has been connected to the international information network. The ERSbeen
included
into the tracking
schedule.
verified by experimental' Etalon 1 ranging by April centimeters is obtained when ranging to ERS-1, Starlette
The station the Smithonian
operation
Astrophysical
has been cosponsored Observatory
contract,
14-1
The
range
capability
1992. The ranging precision and Lageos satellites.
by the DGFI whose
station
contracts
support
ERS-1/7831/91,92
in acknowledged.
has been of
2-3
and
N94-1562 '
C 0 om
L-
0 L.
0
0 e" im
¢D m
0') C I.U m m
u_ X em
era
14-2
14-3
m
"_t0_ im
,m
m
o
0 Z
0 Z
