0 irasSky Survey Atlas - NTRS - NASA

0

iras

Sky Survey Atlas EXPLANATORYSUPPLEMENT

S. L. Wbeelock T. N. Gautier .L Chillemi D. Kester H. McCallon C Oken J. V/bite D. Gregoricb E Boulanger

J. good T. Chester

InfraredProcessing andAnalysis Center JetPropulsion Laboratory

May1994

TheInfrared Astronomical Satellite (IU,S)was a jointproject ofNASA (U.S.), NIVR (TheNetherlands) andSERC (U.K.).

PREFACE

This Atlas

Explanatory

(ISSA)

covers

and

completely

coverage

down

ecliptic plane

the

high

ecliptic

fields

are of reduced

Set.

reduced

residuals.

The

latitude

compared

care

is due

some

be

[_1 > 50°,

in 1991

with

down

rest

product,

of the

ISSA the the

ecliptic

fields

ISSA

by zodiacal using

some covers

to 1/31,_

20 ° of the

to the

when

Survey

in 1992

coverage within

IPAC taken

Sky

release

release

to contamination

should

IRAS

ISSA

ISSA

latitudes

as a separate

quality

first sky,

second

covering

the

and

Reject emission

ISSA

Reject

(§IV.F).

In addition provided File

Set.

The

quality

released

Special

images

to information

in this

(ZOHF),

release

data

Survey

For additional Investigator

S. Wheelock, Pasadena November

which

was

images,

on the described

some

IRAS in the

in this Supplement

Center reader Atlas

are available

(NSSDC) at the Goddard is referred to the NSSDC

1988

at the National Space Flight Cenfor access to the

(ISSA).

information

and

Gautier

concerning

ISSA,

please

Analysis

Center

and

T. Chester

1993

ii

''_tN_.'-_

December

is

History

H).

Institute of Technology CA 91125 T.N.

information

Zodiacal

Support

Infrared Processing Mail Code 100-22 California Pasadena,

3.0,

described

ISSA

Supplement

(Appendix

Space Science Data ter. The interested Sky

on the

Explanatory Version

memo

The

Guest

Reject

of 50 ° > 1/31 > 20 °, with

are

IRAS

ISSA

remaining

therefore The

accompanies

the

to 1/31 _ 40°.

latitudes

13 ° . The

Supplement

'4_- _:_Q_

i,_.e,_

._.;I

i_L_..' '."

contact:

TABLE

Preface

of Tables

Index

of Figures

ii

.....................................................................

vii

....................................................................

ix

INTRODUCTION A.

General

B.

The

C.

The

D.

Cautionary

Overview

.........................................................

I 1

IRAS

Survey

.........................................................

I-2

IRAS

Sky

Survey

Notes

D.1

Absolute

D.2

Point

D.3 D.4

Photometric Confirmation

D.5

Solar

D.6

Residual

D.7 D.8 E.

F.

A.

Ascending Caveats

Low

Responsivity

Due

Angles Scans

SURVEY

History

File

ATLAS

Improvements

A.2

Zodiacal

A.3

Destripers

I 8 I-8

Removal

to Permit

Detector

Coaddition

Baselines

the

Representation

Known Asteroid Removal from the Coadded Full-Sized Detectors ................................................

B.3

Detector

Effective

II .................

........................... of Spatial

Images

.................................................. Method

Response Solid

....................................

.........................................

Angles

...................................... ..°

nl

1

II-1 II-2

Information

Information ...................................... Removal .........................................

Calibration

Frequency

II-1

...............................

A.7 A.8

Source

I-9

......................................

Calibration

to Improve

of Calibration

I--9 I-9

............................................

Improved Particle

Spatial

I 8 I-8

A.5 A.6

B.2

I-7

.....................................

in Atlas

to Stabilize Pointing Radiation

I-7

OVERVIEW

in Relative

Foreground

I-6 I-6

in the

.................................... .....................................

Artifacts

Improvements

A.1

Point

.......................

.................................................

Frequency

SKY

B.1

........

I-7

Effects

to Improvements

Solid

Anomalies

Zodiacal

Overview

Set

.......................................................... Data ......................................................

Spatial

and

I-6 Reject

........................................................

IRAS

Changes

............................................

vs. Descending

Destriper

I- 6

.................................................

Change

A.40versampling

B.

Debris

of Detector

E.4

IRAS

Photometry

Calibration

E.3

I-6

................................................

Photon-Induced

Mosaicking Saturated

I-4

Errors in Low Latitude Images, ISSA of Sources .............................................

System

E.1 E.2

The

...............................................

.........................................................

Source

Processing

Atlas

Radiometry

Accuracy

II.

CONTENTS

..............................................................................

Index

I.

OF

. II-2 II 2 II-2

.................

II II

2 3

II--3 II-3 II--3 II-8

C. III.

B.4

Zero

B.5

Calibration

Product

Calibration

..............................................

Limitations

Description

for Extended

II-8

Sources

.......................

......................................................

II-8 II-9

PROCESSING A.

Time-Ordered

Detector

A.1

Positional

A.2

Calibration

Data

Improvements

Improvements

..............................

...........................................

Improvements

Detector Response Function ................................. Zero Point Calibration .......................................

III-2 III-3

A.2.c

Other

III-8

Calibration

Enhancements

C.

Image

Production

C.1

Empirical

C.2

Zodiacal

C.3

Destriping

Data

.......................

Removal

III-10

.....................................

III-11

........................................................

Global Local

Destriper

Image

Assembly

Destriper

Quality Checking D.1 Pre-Production

Overview

III-10 III-10 III-10

.............................................

Foreground

C.3.b

III-12

..................................

III-12

.............................................

III-13

..................................................

III-18

....................................................... ...................................................

III-21 III-21

.......................................................

III-21

D.2

Production

D.3

Post-Production

D.4

Types D.4.a

of Anomalies ............................................... Data Anomalies ............................................

III-22 III-23

D.4.b

Processing

III-23

Analysis

B.

Positional

C.

Point

D.

Photometric D.1 Point

Overview

Anomalies

III-21

......................................

.......................................................

Accuracy

Spread

IV-1

.....................................................

Function

IV-1

...................................................

IV-3

Consistency ............................................... Sources .....................................................

D.2

Extended

D.3

Absolute

Noise E.1

..................................................

RESULTS

A.

F.

.............................

...................................................... Corrections

C.3.a

ANALYSIS

E.

III-2

A.2.a A.2.b

A.3 Deglitching ....................................................... Time-Ordered to Position-Ordered Detector

D.

III-1 III-1

..........................................

B.

C.4

IV.

Point

Sources

.................................................

Photometry

Performance Cross-Scan

Noise Equivalent Residual Zodiacal

E.4

Quality

ISSA

Reject

Estimates Set

IV-15

.............................................

and Sensitivity vs. In-Scan Noise

E.2 E.3

IV-11 IV-11 IV-15

...................................... ......................................

IV--17 IV-17

Surface Brightness in ISSA ...................... Emission ....................................... From

Background

Scan-to-Scan Analysis

iv

Statistics

...................................

...................

IV-17 IV 18 IV

18

IV-19

V. VI. VII.

FORMATS

FOR

THE

REFERENCES

IRAS

ATLAS

(ISSA)

.........

.............................................

APPENDIX

A.

Center

APPENDIX

B.

Compression

APPENDIX

C.

Pre-Production

APPENDIX

D.

Global

Positions

for

IRAS

Algorithm

Sky

V

1

VI

1

VII-1

Survey

Atlas

............

A

....................................

Anomalies

1

B 1

.................................

C

1

Destriping

D.1

Introduction

D.2

Database

Generation

D.3

Database

Clean-Up

D.4

Intensity

Difference

............................................................

D-1

....................................................

D-1

..................................................... Fits

D--6

.................................................

D 8

D.4.a

Fits

at 12 ttm

.....................................................

D.4.b

Fits

at 25 ttm

....................................................

D

11

D.4.c

Fits

at 60 jml

....................................................

D

14

D.4.d

Fits

at

Monitoring

100 #m

E.

Gain

Errors

APPENDIX

F.

Gain

and

APPENDIX

G.

Zodiacal

G.1

Overview

G.2

Data

G.3

Description

..................................................

D-14 D-15

.................................................. Offset Dust

Corrections Cloud

E-1

...............................

Modeling

Using

...............................................................

.................................................................... of Model

G.3.a

Density

G.3.b

Temperature

....................................................

...........................................................

G.3.c

Emissivity

G.3.d

Cloud

G.3.e

Constant

G.3.f

Model

...................................................... ........................................................

Orientation

................................................

Background Parameters

............................................. .................................................

Fitting Procedure ....................................................... G.4.a Model Results ....................................................

APPENDIX

D 9

.............................................................

APPENDIX

G.4

SURVEY

..........................................................

ACKNOWLEDGMENTS

D.5

SKY

H.

Zodiacal

History

File

IRAS

F

1

G

1

G

1

Data

G 3 G-3 G 6 G 6 G G-7 G 7 G-7 G-9

(ZOHF)

............................................................

H.1

Introduction

H.2

Production

H.3

Format

H.4

Processing

..............................................................

H-2

H.5

Calibration

..............................................................

H-3

Description

..................................................

..................................................................

V

7

H-1 H-1 t-I-2

H.6

Analysis Results H.6.a Gain and

........................................................ Offset ...................................................

H-3 H-3

H.6.b

Position

..........................................................

H-4

H.6.c

Calibration

H.7

Anomalies

H.8

Zodiacal

Verification

...........................................

............................................................... History

File

Version

3.1

........................................

vi

H-5 H-5 H-6

INDEX

II.

IRAS

SKY

SURVEY

A.1

Detectors

Used

B.1

Suggested

Correction

Between III.

ATLAS in IRAS

6' and

OF

TABLES

OVERVIEW

Sky

Factors

2 ° at 12 and

Survey

Atlas

for Spatial 25 pm

Images

........................

II 3

Frequencies

......................................

4

III

3

PROCESSING A.1

Hysteresis

A.2(a)

Equation

Time

....................................................

Constants,

12 pm

..............................................

III-4

A.2(b)

Time

Constants,

25 #m

..............................................

III

A.2(c)

Time

Constants,

60 pm

..............................................

III--5

A.2(d) Time Constants, 100 #m ............................................ A.3 TFPR Model Parameters ............................................... C.l(a)

Field-Groups

C.l(b)

for

Field-Groups

C.2

ISSA

C.3

Planet

and

12 and

25 ttm

for 60 and

ISSA

Reject

Positions

and

.....................................

100 pm

Fields

Corresponding

Comet

ISSA

and

III

Trails ISSA

.................

Reject

Amount

of Data

Removed

in Anomaly

Processing

(1_1 > 20°)

Amount

of Data

Removed

in Anomaly

Processing

of the

ISSA

IV.

Reject

and

Set

ISSA

ANALYSIS

(I/31 < 20 °)

Reject

Fields

....... .......

........................................

Affected

by Saturated

Data

15

III-19

Fields

D.l(b)

ISSA

6 9

III-14

....................................

Containing

4

III III

D.l(a)

D.2

V.

II

..............

III-21 III

22

III

22

III

27

RESULTS

B.1 B.2

Point Sources Used in the Position and Photometric Position Difference Statistics ............................................

C.1

Point

D.1

IRAS-DIRBE

E.1

In-Scan

E.2

Residual

Zodiacal

Emission

Discontinuities

E.3

Residual

Zodiacal

Emission

Gradients

F.1

Parallel

Error

Analysis,

Pixel

Size

= 0.5 °

F.2

Parallel

Error

Analysis,

Pixel

Size

= 2.0 °

F.3

Perpendicular

Error

Analysis,

Pixel

Size = 0.5 °

........................

IV

F.4

Perpendicular

Error

Analysis,

Pixel

Size = 2.0 °

........................

IV-25

Spread

FOR

THE

FITS

Header

1

A Sample

2 3

A Sample FITS FITS Keywords

Center

Dimensions

Transformation

vs. Cross-Scan

FORMATS

APPENDIX

Function

...........

......................................

in ISSA

SKY

for Intensity

16

398 .........................

IV

18

.............................

IV

19

IV

19

..............................

IV

22

..............................

IV-23

..................................

SURVEY Images

6

IV

Field

Header for Intensity Images ............................................................

IV-2 IV-3 IV

.........................................

Noise

IRAS

Analyses

ATLAS

24

(ISSA)

(4 byte

format)

................

V 2

(2 byte

format)

................

V 4 V-6

A Positions

for IRAS

Sky

Survey

Atlas vii

..................................

A-1

APPENDIX

B

B.1 Filter Kernels ........................................................... APPENDIX

B-2

C

C.1 Summary of Pre-Production Anomalies Removedfrom the ISSA Images .. C 1 APPENDIX

D

D.1 Detectors for which Global Destripe ParameterswereDerived ............ D.2 Relationship betweenNumber of DifferencePoints and Order of Fit, 12/tm .................................................... D.3 Relationship between Number of Difference Points and Order of Fit, 25 #m .................................................... D.4 RMS of Intensity Differencesas a Function of Iteration ................. APPENDIX

E-1 E-1 F-2 F-3

(3

G.1 Model Parameter Values and Uncertainties .............................. G.2 Correlation Coefl_icientsBetweenModel Parameters ..................... APPENDIX

D 12 D-15

F

F.1 Statistics of Correction Factors .......................................... F.2 Histogram of Gains ...................................................... APPENDIX

D 10

E

E.1 100 #m Gain Errors ..................................................... E.2 60 tim Gain Errors ...................................................... APPENDIX

D-2

G-9 G-13

H

H.1 Pixel Sizesfor ZOHF .................................................... H.2 Format of ZOHF Version 3.0 ............................................ H.3 Gain and Offset of eachVersion 3.0 Observation Comparedto each Version 2.0 Observation ................................................. H.4 Histograms of Comparison of ZOHF Positions with the Observation Parameter File .............................................

°°,

vln

H 1 H 2 H 3 H-4

INDEX

I.

II.

III.

FIGURES

INTRODUCTION B.1

Schematic

Drawing

of the

Orbital

B.2

Schematic

Drawing

of the

IRAS

IRAS

SKY

SURVEY

ATLAS

Geometry Focal

Plane

..............................

I 3

..............................

I-5

OVERVIEW

B.l(a)

Plots

of IRAS

detector

response

vs.

dwell

time,

12 and

25 itm

B.l(b)

Plots

of IRAS

detector

response

vs. dwell

time,

60 #m

................

B.l(c)

Plots

of IRAS

detector

response

vs.

time,

100 g.m

dwell

.........

II

5

II-6

...............

II

7

C.1

ISSA

Fields

for 1/31 > 50 ° in Equatorial

Coordinates

.....................

II

10

C.2

ISSA

Fields

for I/?1 > 20 ° in Equatorial

Coordinates

.....................

II

11

C.3

ISSA

Fields

for 1/31 < 20 ° in Equatorial

Coordinates

.....................

II

12

PROCESSING A.1

Point

C.l(a)

Source

Hysteresis

Field-Group Destriper

C.l(b)

Comparison

Boundaries

100 tm_ 25 #m

.........................

III

for 60 and

Processing

III

100/,nl

as Seen by IRAS Plane Anomalies

D.2

Distribution

of Mini-Streak

D.3

Distribution

of Local

D.4

Occurrence

of Saturated

and

Destripe Data

................................. .................................

Detector-Streak

Anomalies

Anomalies

for

for Entire

Sky

............

IL/I > 50 ° ................. ..........................

Histograms

of Position

Differences

in RA

Histograms

of Position

Differences

in DEC

C.l(a)

Contour

Plot

of Point

SI)read

Function

for a 12 /ml Source

C.l(b)

Contour

Plot

of Point

Spread

Fnnction

for a 25 ttm

Source

C.l(c)

Contour

Plot

of Point

Spread

Function

for a 60 t,m

Som'ce

...........

C.i(d)

Contour

Plot

of Point

Spread

Function

for a 100 ttm

Scatter

D.2

Flux

APPENDIX

III

17

III III

20 24

III

25

III

26

III

28

RESULTS

B.l(a) B.l(b)

D.1

16

Local

...............................................

Known Contet Trails Distribution of Focal

7

Local

...............................................

Boundaries

C.2 D.1

ANALYSIS

--

for 12 and

Processing

Field-Group Destriper

IV.

OF

Plots Density

of PSC

vs. ISSA

vs. Aperture

Point

Between

Source

Diameter

PSC

Between

Fluxes

and

PSC

ISSA

IV

4

IV

5

...........

IV

7

...........

IV

8

and

....

ISSA

Source

...

IV

.........

IV

..................

IV

...................................

9 10

12,13 IV

14

D

D.1

Distribution

D.2

Histogram

of boresight of boresight

intercepts crossing

for the counts

D.3 Proliferation D.4(a) Intensity

of detector intercepts residuals (HCON-1 and

D.4(b)

Intensity

residuals

D.5(a)

Intensity

differences

(HCON-3) along

per

focal

plane

fractional

100/an HCON-2)

crossings scan

..........

segnient

............................ at 12 ttm .................

12 mn ...............................

a single ix

detector-scan

track

with

.......

D 3 D 4 D 5 D 7

D 7 a

sixth D.5(b) Plot

D.7

Intensity

of points

class

along

differences

F

F.l(a)

Gain

and

destriper

a detector-scan

along

for detector

track

..........

D-13

42 (25 #m)

illustrating

...

a

track

illustrating

a D-19

a detector-scan

track

illustrating

a

....................................................... that

offset

have

close

corrections

extreme

versus

D-17 D-19

a detector-scan

along

anomaly

segments

APPENDIX

global

13

a

.......................................................

differences

Scan

by the

track with algorithm

.......................................................

IB anomaly III

D

along a single detector-scan dual-hemisphere-with-overlap

rejected

differences

Intensity class

D.10

.......................................................

IA anomaly

Intensity class

D.9

fit

Intensity differences fit derived with the

D.6

D.8

order

D-20

point

pairs

elongation

and

for

100 #m

SOP,

fits

12 #m

.....

D-21

.........

F-4

F.l(b)

Gain

and

offset

corrections

versus

elongation

and

SOP,

25 #m

.........

F 5

F.l(c)

Gain

and

offset

corrections

versus

elongation

and

SOP,

60 #m

.........

F-6

APPENDIX

G

(3.1

ZIP

data

(3.2

The

scanning

(3.3

The

IRAS

(3.4

A typical

IRAS zodiacal

(3.5 (3.6

showing

bandpasses

Data

and

solar

elongation

Data

and

solar

elongation

APPENDIX

zodiacal

geometry

brightness of the

and dust

zodiacal

dust of 67 °

satellite

scan

cloud

with

model

the

of solar

elongation

prediction

dust

cloud

for a scan

model

prediction

(3-2 (3-4

........................... zodiacal

(3 5 model

fit

(3-10

at

................................................ cloud

...

.............................

a 200 K blackbody

pole-to-pole of 112 °

as a function

IRAS

(3-11 for a scan

at

.................................................

(3-12

H

H.1

Flux

H.2

Mean

ratio

at NEP

flux ratios

vs. time

from

vs. time at NEP

SAA

crossing

from

and

SAA

population

crossing standard

...........................................

.........................

H-7,8

deviations H-9,10

I.

INTRODUCTION

A. General Overview The

Infrared

low Earth a ten

month

produce from

Astronomical

orbit

in four

period

within

the

radiometry

original

extended

brightness

(IRAS

was

The

and

were

data now

products. the

IRAS

available Each spaced

are

1991,

completely

191_

40 °.

some

coverage

many

The

tor

destriping

the

SkyF1ux

features for

IRAS

spatial

Sky

solar

ISSA

system.

IRAS

survey

Catalog

1988, ed.

ecliptic 13°-

images.

Atlas

to

detectors data.

The surface

between

1984

C. A. Beichman

This

(§III.C.3)

result

at short at

are cannot

of the

be used

increase

25 #m.

region)

to give

relative

for determining I-1

the

is the latitude.

limiting

noise

photometry the

in

down

to

-20

because

° of

contaminated

by

Set

for

data

is usable

for photometric Supplement

infrared

combination

foreground

noise

are

calibrated

The

20 ° ecliptic

bands

release,

latitudes

Explanatory

is enough

Detector

above

with

Atlas.

of a factor

This

sky

coverage

Reject

Atlas

5'.

zodiacal

wavelengths.

locations

designed

than

the

so named

these

of the

(IPAC)

reprocessing

first

ecliptic

fields

consistently

larger

in a sensitivity

at 12 and most

Survey

Center

declination

some

ISSA

using

formats

is to present scales

of most

IRAS

when

original

covers The

Set,

These The

accuracy

of 50 ° > I/_l > 20 ° with

between

ISSA.

Sky

and

with

Reject

bands.

IRAS

analysis

for ISSA

fields

be taken

ISSA.

the

of the

of the

10 ° along

latitudes

ISSA

of the dust

should

at spatial

removal

invisible

rest

ISSA

(I/ 1 > 50°)

the

Analysis

The

every

ecliptic

photometric

results

of the

from

sensitivity.

analysis

The

releases

remaining

zodiacal

and and

(ISSA).

emission

unprecedented

and

centered

covers

The

§IV.F).

IRAS

two

product,

care

(§III.A.2),

They

Processing

latitudes

to the

and

motivation

images

Infrared

in 1992,

production,

scales

of infrared and

improved

are

20 ° of the ecliptic plane (the ISSA Reject bands and residual zodiacal emission. The

in the

Survey

There

high

and

sky from

view

resolution

the

_pecial

the

images

a broad

angular

to produce

compared

but

previously

small

infrared

Source

Accordingly,

residuals

(§I.D.3

improvements

Point

was

unobtainable

of 16.5 ° square

Supplement,

production

to I_1 _

quality

scientific

gave

high

as a separate

in detail

entire

the

during

survey

IRAS

consisting

in sensitivity

release,

down

applications

of the

IRAS

Explanatory

is a 12.5 ° x 12.5 ° region

second

emission

describes

with and

gained

covers

measurements

the

of the

improvements

10 ° apart.

released

reduced

zodiacal

with

images

large

data

field

The

20 ° are

sources

of the

at a sensitivity

knowledge

as the

which

their

along

with

that

using

430 fields.

to

system

however,

reprocessed are

solar

obtainable

IRAS

stability

100 #m

D.C.:GPO)).

the

clear,

good

of 98% of the sky from

purpose

sources

as SkyFlux

Atlases:

16.5 ° x 16.5 ° SkyFlux

Galaxy It was

known

released and

The

The

point

astronomical

atlas,

a survey

of 12, 25, 60 and

1983.

of infrared

atmosphere.

Catalogs

conducted

wavelengths

to November,

catalog

of extended

et al. (Washington

(IRAS)

effective

January

emission

images,

1986

with

reliable

Earth's

allowed

and

from

an extremely

Satellite

bands

absolute

images

of calibration

(§III.C.2), greater

and than

to reveal

detec-

five over

Galactic

limiting

noise

dust of ISSA

At latitudes is due

within

to zodiacal

for objects sky surface

dust

outside brightness.

the

Section §II.B gives important details about the calibration of IRAS. IRAS

results

with

the

Background

Explorer

quantitative

photometric

The

remainder

Diffuse

Infrared

Background

(COBE)

satellite

should

measurements

of this

for the

and

correct

Introduction

use of the

improvements

made

Chapter

III gives

presents

results

the

formats

B.

The

a description from

of the

IRAS

details

to as the

and

survey

IRAS Earth's allowed

the

pointed

exactly

to point

plane

are

and

was

An

released

used the

images

aspects

overview

of the

of the

is presented

to produce

ISSA

90 ° from

the

angles

long Main

Sun.

from

Reject

the

for

IRAS

changes

in Chapter

II.

Chapter

IV

Atlas.

images.

scans

Chapter

V details

by

polar of the

survey

to complete

of 75% of the

called

sky

survey

IRAS

instrument

used the

the ability surveys

ten month

in which

way

a double

the

centered

would

if it had

have

remained

of the satellite of 98% of the

operating

period

(Main

Supple-

CONfirmation

scans

In this

over

of circles geometry

two confirming

for Hours

scans.

orbit

six months

strategy

of Sun-centered

altitude

portions

This

sky within

an HCON

1/4 ° between

IRAS

at 900 km

along

sky in exactly

IRAS

the

extensive descriptions of the Supplement 1988, hereafter

orbit

the whole The

instruments,

reference.

§III.B).

was accomplished by scans separated from one scan to be correlated with HCONs (HCON-1 the IRAS mission,

and

of the

Supplement,

of a series

moved

telescope

descriptions

for easy

tile Sun

survey

survey,

consisted was

here

to view

confirming

§III.A),

IRAS

a Sun-synchronous

and

telescope

confirming

of the

Short

included into

I.B.1

IRAS

array

atlas

processing

designs

to facilitate

(Figure

sky and a third of the satellite.

ment,

on those

is also presented.

ISSA

Supplement.

launched

at varying

Each

a refresher

data processing system, along with contained in the IRAS Explanatory

Main

terminator Sun

images SkyF1ux

of the

of the

design

was

on the

ISSA

images.

and the IRAS products, are

referred the

ISSA

using

Cosmic

to understand the ISSA images. It will define the in this document. A collection of cautionary notes

of the

analysis

before

on the

of

Survey

Complete sky survey IRAS data

the

(DIRBE)

be understood

provides

ISSA

since

comparison

(§IV.D.3).

telescope and the IRAS survey needed terms and introduce the concepts used vital

Experiment

The

the

1/2°-wide

coverage

focal

of the

sky

by up to 36 hours, allowing point source detections other scans to confirm the reality of detections. Two

and HCON-2) were performed with the second HCON lagging

concurrently behind the

in the first six months of first by a few weeks. Solar

elongation HCON-1

angles, e, of the telescope line of sight were roughly confined to 80°-100 ° during and HCON-2. The third survey, HCON-3, was begun after the completion of the

first

and

two

cover

tile

when

it was

used

whole

sky

full available in less

terminated

A significant from

the

interplanetary

than

range

of solar

six months.

by exhaustion

feature

of the

IRAS

dust

in the

solar

of the survey system,

I-2

The IRAS

elongation

(60°-120

°) in an attempt

third

HCON

was

liquid

helium

supply.

strategy presented

is that

zodiacal

a constantly

only

75%

emission, changing

to

complete

arising source

of

NORTH PO LE

EARTH-SUN

SUN

3.85 ARCMIN PER SECOND SCAN RATE

LINE

1 DAY

DETECTOR ARRAY

EQUATOR/

LATER

\ \ \ \

\

Figure

I.B.1

900 km,

and

inclination,

a precession plane

A schematic of the

constantly

By pointing shielded

from

scanning

motion

confirming

foreground the

emission

celestial

surface through

sphere

brightnesses the

zodiacal

heat across

scans

on the

through separated because dust

of the

the

satellite

the

of tile orbital

99 °, combined

plane

faced the

drawing

with

orbit

the

of about

Sun as the satellite radially

loads

away

from

sky

celestial

sphere

which

IttAS

Sun

the and

in about

observed.

equatorial day.

near

the

Earth

cold

while

altitude,

bulge,

As a result, the Earth's

Earth,

Two

the

moved

This

orbital

led to

the

orbit

terminator. telescope

providing

A sequence

was

natural of hours-

is also shown.

as a few days

Earth

The

six months.

by as little cloud.

Earth's

1 ° per orbited

from

the

tile entire

geometry.

in its orbit

variation I

observations

would

3

produced

measure and steep

of the same significantly

changed gradients

the

point

on

different line

of sight

in individual

HCON images where adjacent locations on the sky were scannedat different times. This prevented direct co-addition of separateHCONs. The variation in zodiacalforegroundwas most troublesome at 12 and 25 #m (15%to 30%dependingon the HCON) which fall near the peak wavelengthof the zodiacal emission. At the longer wavelengths,diffuse Galactic emission becomesnmch stronger than zodiacal emission, reducing the effects of zodiacal variation. The focal plane array of the IRAS survey instrument consistedof 62 detectors with either 15 or 16detectorsat eachof the four IRAS wavelengths(Figure I.B.2). The telescope wasoriented sothat, during survey scans,the imageof the skymovedacrossthe array in the long direction at 3.85' s-1, producing complete coverageof a 0.5°-wide swath of sky. The four staggeredrows of detectors in eachwavelengthband weredesignedto provide slightly more than 100%overlap of the detectorsduring a single scan. This provides slightly more than two samplesper detector in the cross-scandirection, which substantially undersamples the telescopepoint spread function at the shorter wavelengths. Sampling rates of 16, 16, 8 and 4 samplesper secondof the 12, 25, 60 and 100#m detectors, respectively,combined with the 3.85' s-1 scanrate and the detector widths of 0.75', 0.75', 1.5' and 3.0', givesabout a 50% oversamplingin the in-scan direction. All 62 detectorsdid not operate correctly in orbit. Two nearly adjacent dead 25 pm detectors and one dead 60 pm detector left holes in tile focal arrays C.

plane

(Figure

The

swath.

Sky

IRAS

Sky

Survey Survey

12.5 ° x 12.5 °, with zodiacal Fields

emission were

every

The

IRAS

requirements, to

an

in the

The data,

survey

array

in-scan

the data field and

first

detectors

step

resolution

affected

the

12 and

the

same

processing the

in the

25 #m

process

Separate examined

point

4.7'

of this

Section

with

higher

spatial

To reduce the

ISSA

time-ordered FWHM

at

processing

images

detector 12, 25,

60

independently

to rephase

centered

rest

was

data and

100

for each

the

data

streams

the

smoothed

to

streams #m,

detector to sample

sky.

emission stability

direction.

introduced

in order

line on the

a zodiacal zero

were

the

a sky.

images.

to produce

second, and

The

measurements

cross-scan

(minus

field on the

12.5 ° x 12.5 ° regions

ISSA

brightness

3.6'

delays

cross-scan

removed detector

into images. were visually

3.5',

430

images,

brightness

a specific

10 ° apart.

of the

reduction

per

sky surface within

into

spaced

in the

data

samples

B). Time

sky

sky

than

resampling

entire are

sky surface-brightness the

wavelength

processing

produced

of 3.5',

represents

IRAS

which

in the

at two

and

the

direction

(Appendix

refined

image

bands,

features

smoothing

simultaneously

Each

at a particular

salient

resample,

in-scan

respectively

blind

is a set of machine-readable

by partitioning

the

and

pixels.

declination

in the

smooth

1.5'

defined the

resolution

or partially

Atlas Atlas

model)

10 ° along

summarizes

noisy

I.B.2).

IRAS

The

Four

model

with

two

from

destriping

algorithms

and and

rephased binned

images of the individual HCONs were produced for each to allow identification and removal of artifacts (§III.D.3).

After removal of artifacts by editing the time-ordered for each HCON and all HCONs were then co-added.

I-4

data, new images Known asteroids

were produced remain in the

WAVELENGTH BANDS, ,um

II//

r'xr'_ -i x

22 2630

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\

I

I

I

IMAGE

I_ [ Fv,s,B,._

DIRECTION

STAR SENSORS Figure

I.B.2

rectangles filter the

and

Y direction

individual ISSA

Auxiliary Due

statistical available The

noise upon

dust artifact

images

of sky coverage

were

removed

images

not

are

image

filled-in

but

included

some

These

features

include

planets,

unknown

process. objects, sources.

of a source detectors

from

the

noise

numbered

of a detector,

the focal

inoperative,

prior

utility

The

of view

during

data

released

plane.

crossed were

statistical

limited

in the

contain

nonconfirming

field

the

plane while

the

mission.

to producing were

in

the

co-added

also produced

(§III.C.4),

the

set of images.

for each

sky coverage

They

are,

and

however,

at IPAC.

images

nonconfirming

focal

the

performance

and

and

IRAS

represent

degraded

images

for instance),

removal

The

showed

constraints

HCONs.

bands,

The

as indicated.

request

of the

each

combination.

to volume

co-added

individual

drawing

portion

detectors

HCON

field.

central

field lens

cross-hatched

images.

A schematic

in the

The both

remaining

individual

to avoid

features

fine structure asteroids HCON

confusion

I-5

with

that

do not

in the zodiacal

confirm cloud

among (the

and

orbital

debris

that

images

enable

users

to identify

confirming

sources

and

the

zodiacal

escaped to study

the these the

D.

Cautionary

D.1

Absolute ISSA

Radiometry

was

emission, sky

Notes

over

surface

25 #m

designed

to provide

spatial

scales

brightness.

100 #m

bands

are

in the

(§II.B.4

affected

above

correction,

§II.B

scales (§IV.D.3). the IRAS-DIRBE

data,

the

accuracy

of the

of this

comparison.

D.2

Point

Source

Photometry

with

this

Survey See

is designed

to study for sources

(Moshir

§IV.C

Photometric

rest

The images of the ISSA

bands. ten

The

times

images

D.4

et al. 1992)

should

than

the

in the

to

or anomalies

the

residual

(§III.C.4). examined

offsets.

25 #m,

background useful

at the

in the

Catalog

in the at

frequency

spatial

scales

region.

If special

reject

data

2, and

and

the

images

errors

are smaller

longer

wavelengths.

Faint

with

been

Source sources.

ISSA.

Set

reject

compared to the the zodiacal dust

region

is taken

remain than

not

by

analyzed

on point

measured

in the care

has

IRAS

information

Reject

work. IRAS

not be impacted

are of reduced quality emission residuals and 25 #m

of this in the

are not optimally

sources

ISSA

at 12 and the

All

measurements.

will

survey

for survey

Images,

and

sources

Version

of point

ecliptic plane by zodiacal

errors

at

when

can

estimating

scientifically

at 12 and

be up to the

useful.

25 #m,

At 60

making

the

of Sources increased

are

visible

objects that appear satellites, asteroids image.

Latitude

12 and

G) and

detector

for quantitative

is not

5 _. Point

accuracy

nonreject

at 12 and

especially

Confirmation Due

background

than

be consulted

of expected in Low

calibration

Source

within 20 ° of the due to contamination

(§IV.F)

100 #m,

reject

Point

Errors

worse

of the

measurements

images

structures

smaller

IRAS

residual

background and

The

for discussion

D.3

at

Appendix

scientists to understand the calibration diffor measurements of sky brightness on large

source

extended

absolute

is dominated and

60% at 100 #m exists

ISSA

zodiacal

sources.

brightness

using

point

for accuracy product.

relative

with COBE DIRBE data

IRAS

results

ISSA

the

point

IPAC newsletters will contain any updated results comparison indicates an uncalibrated nonlinearity

the

optimized

at 60 #m and

before

There is an ongoing effort ferences between the IRAS and

error

of the

for determining

(§III.C.2

knowledge

of these

removal

be used

zero

model

by imperfect

as 30%

after

cannot

absolute

by both

affects

Read

5 t. ISSA emission

III.A.2)

which

photometry,

of the

extent

of as much

a few degrees.

spatial Unless

than

zodiacal

and

to some

An uncertainty response

larger

Uncertainty

by uncertainties

60 and

differential

No confirmation

sensitivity than

in the

of the

ISSA

SkyFlux

images,

images.

more

nonconfirming

Nonconfirming

objects

in only one HCON intensity image. These objects or space debris. If not removed, they can appear co-adder

was

implemented

in producing

the

are

those

may be orbiting in the co-added

co-added

Therefore, for each ISSA field, all individual HCON intensity visually to identify objects appearing in only one HCON image. I-6

objects

ISSA

image

images were When found,

the contaminated portion of the offending scanwasidentified and removed.Lessthan 1%of the entire survey databasewas removedby this visual inspection process(§III.D.3). Even though great care was taken to remove anomalies, some remain in the co-addedimage. Individual HCON imagesshould be examined to verify the reality of unusual features in the co-addedimage. D.5

Solar

System

Emission

from

includes

some

This Some

asteroids

publication

some

remain

Both

comet

tails

by either

radiation

pressure,

418).

Comet

along

the

images

orbit

visible

Residual

tion

due

that

are

Point

expected source

At 60 and Galactic

change

depending

plane.

photon-induced

Compared

scan

responsivity

Improved

image

The

Change solid angle

functions §II.D.2). products, to Main

trails

and

The

tails, blown

tail

pole

of comet

(fields

416

pressure,

of time.

is found

will

comet

particles

and

spread

In the

perpendicular

sky,

sources

enhancement,

Some

ISSA

to the

in §III.C.4.

scan

Planets

§III.C.4.

remain

of the

data. due

around

photon-induced See Main

than

at less than

the

images

in the

ISSA

or hysteresis

brighter

sources from

effects

direction.

period

nearly

latitude

point

co-added

effect

sun.

1986

plane at ecliptic ISSA Reject Set. with

ecliptic

a long

comet

Sources

removed

hysteresis

HCONS

to radiation

image

lower

around

tails. not

in the

on the

Calibration

response 2 1992,

source

100 #m,

as the

were

north

planets.

removed.

or neutral

to the

and

as of the

were

associated

wind

confusion.

Effects

background.

to have

tails

over

the

responsivity and

the

the

by known

appear

asteroids

1986)

Dust

insensitive

crossing

Responsivity tails

near

debris

cover

trails

in different

is closest

accumulate

affected

fields

strength

from a single point several directions.

nal

fields

in ISSA

to a photon-induced

at 25 #m

D.7

and

can cause

comet

known

(Matson

by solar

comet

images

as streaks

resembling

of source

tails.

comet

appear

only

data.

blown

the

tails,

aspects

in the

of larger

Photon-Induced

Artifacts are

of the

since

and

bands parallel to the ecliptic by the dust bands are in the

particles

in some

comet

in different

seen

in the data

Survey

emission affected

are

composed

trails

Comet

seen

when

is visible

A list of ISSA

also

trails ionized

bands,

images

and

are

appear

trails,

comet

direction.

and

charged

IRAS-Araki-Alcock

D.6

bands

remains

dust

co-added

Asteroid

dust

material

zodiacal

as nonconfirming extended less than 15 °. The images

caused

are

system

in the

IRAS

zodiacal

appear latitudes

solar

asteroids,

of the

The

by

Debris

effect,

The

that

these than

to point

sources

bright

and

thresholds one

areas

tail being

around

§IV.A.8

20 Jy

may may

have

radiate

scanned

(within

brightness

tails

is a func-

15 Jy at 12 pm

More

Supplement

images.

in

_ 6 °) such sources

will

for explanation

of

enhancement. Due

to Improvements

estimates

in the Accuracy

were derived

for each

detector

of Detector based

Solid

Angle_

on two-dimensional

(see Explanatory Supplement to the IRAS Faint Source Survey Version The improved solid angles differ from those used in making the origie.g.,

SkyFlux

Supplement

and Table

IRAS IV.A.1 I-7

Zodiacal the

average

History of new

File

(ZOHF)

effective

Version solid

angles

2.0. for

full

size

detectors

decreased

values.

100 #m

D.8

Several the

vs.

with

Earth

is about

2%

north

ecliptic

pole

at

asymmetry

angles

ZOHF

2.0 and

Version

(scans

has

100 #m,

an inverse

Version

slightly

while

ascending 60 #m, the

is a real feature

and

respectively,

effect

and

on calculated

3.1 will be fainter

brighter

at

12, 25

at 60 #m.

3.0 (§I.F

and

with

decreasing

progress

plane

In the

12 and

between

2.0

which

than

IRAS

the

ascending

orbit,

scans 1.5%

look

25 #m,

and

Appendix

4%

descending

scans.

sky cannot

be ruled

1/31 > 50° can be mosaicked

without

are

progress

look

behind

magnitude

100 #m

of the

as seen

Analysis

part of the ascending-descending drifts. However, the possibility

of the

which

always

The at

found

latitude)

(scans

scans

ahead.

and

H) have

ecliptic

scans

descending

always at

ascending

in Appendix H shows that a large attributed to uncorrected calibration of the

at 12, 25 and

Scans

latitude).

in its orbit

effect

in the

Version

at the ecliptic

ecliptic

6%

in the solid

values

ZOHF

scans

brighter

increasing

the

of the

descending

systematically

the

to ZOHF Descending

users

8% and

A change

Therefore,

compared

Ascending

that

by 13%,

by 3% at 60 #m.

intensity and

increased

at

the

as described

asymmetry can be that some small part

out (Dermott

1994,

submitted

to Nature). E.

Processing

E.1

Caveats

Mosaicking All images

to

an

accuracy

destriping

the

where

accuracy of 1-2

Saturated An error

well as the

entire

images occurs

it is not

latitude

MJy

sky,

(§III.C.3.b).

as those

was found

the

effect

This

capability

brought

all

is due

confirming

offset

to the

adjustments

use

coverages

of a global

of the

sky

to a

1/31 < 50°,

Fields

in the

in the

I/3t > 50°

1/31 < 50 ° sky join.

sr -1 at 60 #m

and

were

latitude

sky except

At these 3-5

processed

lower

MJy

near

differently sky can

from

the

the

be mosaicked

Galactic

two locations,

ISSA

plane

and

field boundary

sr -1 at 100 #m are

measurable.

Data

eliminated in the

sr -1. which

lower sky

I/3t > 50 ° sky and

discrepancies E.2

the

1/31 > 50°

same

the

MJy

additional

level.

covering

in the

0.1

(§III.C.3.a),

background

Fields with

of about

algorithm

Common

fields

covering

wrong

set of ISSA

while mainly

considered

in the algorithm

detector some in the

when images.

for handling

saturation

As a result,

nonsaturated Galactic

a significant

intensity plane

where

problem

since

values

intensity affects

values.

the SkyF1ux

intensity

were

60 and

it affects

8

and

saturated the

(§III.D.4.b).

I

saturated

occurred

values

erroneously 0.1%

error

images

were

as

included

eliminated.

100 #m detectors less than

The

saturate, of detector

This but data

E.3

Destriper

Anomalies

An error

was found

algorithms 50 ° sky.

This

removed

in the

13).

Low

magnitude

of the

Frequency

zodiacal model.

part

25 #m

around

discontinuity. marks

The

the the

60 ° point.

Thus

part

of the

this

longitude effect

year.

change

The

at

destriper

destriper

0.5 MJy The

were

remain

is about 0.5 °.

1/3[ >

problems

anomalies

location than

destriper

in the

at 4h31m46.5s:-63d40m15s

in the (ISSA

sr -1

software

An

example This

at

12 and

was

part

of the The

sky was peak

° ecliptic

by looking

fixed

for

is roughly

viewed

and

of the

where

later

discrepancy

dust

band

sr -1 at 12 #m,

local intensity prior to zodiacal emission removal. For 12 #m is roughly 5% of local intensity prior to zodiacal

overlap

240 ° point leg

through

in the

to the

a different

intensity

along

is enhanced

at

by a

a different

which

a

Six months

ascending

change

the

the

survey.

the

ISSA

at 12 and

mission

leg and

in

through

occurs

HCON-2 and

in the

observed

to as the

six months

a zodiacal

2.0 MJy

were

descending

240 ° point

latitude,

to imperfections

of a discontinuity

magnitude

through

sky

is referred

HCON-1

to the

due

or gradients

of the

of the

leg of the

images

discontinuities

the beginning

cloud.

ISSA

regions

longitude.

progressed

in intensity

in the

sharp

cloud.

marks

-15

caused

remain

ascending

same dust

occurs

geometric

dust

leg had

the

scans

is visible less

adjacent

240 ° ecliptic

of the

zodiacal

short,

Although

some

at this

as either

where

60 ° point

descending

effect

is seen

zodiacal

beginning

anomaly

effects

occur

60 ° and

data.

for one of the

for some

Artifacts

This

of the

the parameters corrections

(§III.D),

is very

emission

Discontinuities

derived in poor

1% of the

process

anomaly

Spatial

different

later

the

I/3[ < 50 ° sky.

zodiacal

images.

than

destriper

the

Residual the

less

that

resulting

checking

A typical

Typically

processing E.4

affects

quality

The

25 #m.

for ISSA,

error

[/_[ > 50 ° images. field

in the software

implemented

is about

time

of

7% of the

1/31 > 50 °, the worst discrepancy at emission removal and about 2% at

25 #m. In addition

to discontinuities,

Galaxy

remain

and

zodiacal

F.

the The

IRAS

The produce and

all

ZOHF

Version error

found

History

and

and

The

in each ISSA

band

3.1 of the in Version

images

IRAS

ISSA

artifacts

not attributable

between

the

zodiacal

to the emission

(§IV.E.3).

time-ordered

data Version

is a time-ordered

of the

survey

is that

standard

ZOHF

3.0.

problem

the

For

ZOHF

additional

was

I-9

have

been

important

retains

the

intensities

1990

were

used

in December

of the

An

in May the

in §I.C

released

information

released

affected

described 3.0, record

array

a 0.5 ° x 0.5 ° beam.

survey.

The

scale

to differences

File (ZOHF)

ZOHF

to produce the

due the

rephased

versions.

the

are

angular

File

History

intervals

large

in producing

Zodiacal

detectors

as observed during Appendix H.

These

used

resampled

IRAS

all subsequent

eight-second

images.

model Zodiacal

same the

in which the

in the

other

entire added

IRAS

zodiacal on

and

the

dust ZOHF

corrected

of a very

survey

together

difference

small

to

1988, over

between emission refer

to

a single number

of ZOHF samples in Version 3.0: none at 12 #m, one at 25 _m, one at 60 #m and 382 (0.03%) at 100#m. The affected sampleswere lowered 23% on the average,with a maximum decreaseof 45%. The description and analysespresentedin the IRAS circular accompanyingVersion 3.0 and in Appendix H of this Supplementare not changedby this correction. The ZOHF is also available with the zodiacal emissionremoved. This product was made by subtracting the zodiacal emissionas predicted by the J. Good model (Appendix G). The Zodiacal Emission RemovedZOHF is available from IPAC by special request. In responseto requestsby IPAC General Investigators, two additional versionsof the ZOHF wereproduced and releasedby IPAC. A version of the ZOHF was generatedgiving eachpixel the maximum in-scanresolution of 2_while maintaining the 0.5° resolution crossscan. This product is known as the 2t In-scan ZOHF and was produced for the purpose of studying the zodiacal dust bands near the ecliptic plane. The Bright Point Source Removed (BPSR) ZOHF was produced in responseto a user request and was generated by removing flux contribution due to bright point sourcesand associatedtails. Point sourceswere identified using the IRAS Point SourceCatalog. Detector samples within a 10' radius of the known source and along the sourcetail were removed from the scan data prior to computing an eight-secondintensity average. Under certain conditions this algorithm produced a nonphysical increasein a 0.5° x 0.5° pixel brightness compared to the brightness in the ZOHF Version 3.0. This can occur in areaswhere sourcesare fainter than surrounding structure. Due to this discrepancy,IPAC recommends that special care be taken

when

All released Coordinated

using

the BPSR

ZOHF

products

Request

and

ZOHF. as well as the User

Support

ISSA

Office

NASA/GSFC Code 633.4 Greenbelt,

MD

20771.

I-

10

are

available

(CRUSO)

through:

II. A.

Changes The

that the

and

limited

the

electronic

60 #m

bands,

The intrinsic The

images.

making

interpretation

detector

removal

HCON resolution

of the

and

largely

zodiacal

faint

without reduced

emission

increased reduced

factors similar

of 2-3 at 12 and 25 #m and 1.5 2.0 for 60 and noise in the in-scan and cross-scan directions. of v_

faint

improvement

structure

quality A.1

over

at 12, 25 and

of the

ISSA

images

in Relative

When

at uniform

measurements

due

calibration,

these

perfections

a factor

images.

No

pendix

G was

of the

individual

removed

or better

artifacts

due

effects

of the

is not

perfect,

moved

the

compared

0.5 MJy

foreground

sr -l

and

images

zodiacal

of the

foreground.

over

the

SkyFlux noise

by

in images with an additional

co-added

images

reveal

Details

of the

images.

of the

reduced the IRAS

appear

different

With

perfect

uniform.

in the

images.

Any

used

source

im-

Calibration

detector-to-detector calibration

model

detector

subtraction

data,

of the

stripes in the

by

SkyFlux

calibration.

described

was

removal

survey.

data.

Since

the

zodiacal

errors

1.0 MJy 1

data, IRAS

in some

places

and

for ]/31 > 50 ° are sr -1

at 25 ttm

over

and

Ap-

co-addition

resulted

the

removed

II-

useflfl

model

during

in the

foreground

in §III.C.2

permitting

zodiacal

non-zodiacal-removed

foreground

and

sky

point

emission

to the

12 #m

will give

Coaddition

zodiacal

remain

the

to the

a band

responsivities.

striping

relative

foreground at

within

baselines

affected

The

in zodiacal

Residual

level

IV.

detectors

time-ordered

images.

insufficient

to the

the sensitivity

The

to Permit

reduction,

in others.

background,

have

to changes zodiacal

images 12, 25 and

the detector-to-detector

SkyFlux

and

25 #m

by the

from

the

in the

in §III.A.2,

Removal

HCON

from

images.

equal-sized

removed

12 and

predicted

stripes

HCON

in detector-to-detector

changes

Foregro'and

A foreground

fold

are

at

co-

interpolation.

invisible

in detector

described

of ten

calibration

Zodiacal

sky,

result

for ISSA,

roughly

A.2

variations

SkyF1ux for the

100 #m. This results Coaddition provides

in Chapter

artificial

prevented

Calibration

to variations

in calibration

enhancements

totally

will be found

Improvements looking

individual

60 #m

and spatial

steep,

data

residual

destripers

by roughly

regions

and

and

of the

detector

interference

images

factor

The

2' pixels

the

bright

images;

features

further

include §IV.A.8),

responsivity

producing

sky

the

difficult

problems

around

SkyF1ux

foreground

problems

Supplement

in detector

in the

Finally,

several

These

(Main accuracy

time-ordered

eliminated

of five.

to correct

images.

variations

of the

foreground

a factor

#m;

obscured

of all improvements noise

SkyFlux

zodiacal

which

designed

striping

observed

images,

the

was

photometric

100

prominent

of the

OVERVIEW

enhancement

degraded

produced

individual

images of the

60 and

sampled

combination

ISSA

responsivity at

SkyFlux

ATLAS

Atlas

usability

which

variations

of the

the

and

plane

that

in the

critically

in

photon-induced

Galactic

temporal

addition just

sensitivity

offsets

gradients

SURVEY

created

as hysteresis,

as the

and

that

of the

known

such

SKY

Improvements

processing

effects

also

IRAS

in a five-

in gradients However, emission too

much

3 5% of the scales

and some model was

re-

original

of 10 ° . For

50° > 1/31 > 20*, the residualsare 1.0 MJy sr-1 at 12/am and 2.0-2.5 MJy sr-lat 25 #m over scalesof 10°. The zodiacal emission model assumeda physical dust distribution which did not inelude the dust bands. The dust band emissionremains in the data and produces artifacts in the images at low ecliptic latitudes, the ISSA Reject Set. A.3

Destripers Stripe

noise

uncalibrated globally

to Stabilize due

1988).

average

of all other

At each

varying

destriping

of a particular to the only

a 10%

A.4

on

1.5'

scan

of every

best

detector.

to make

further The

left

for the

used

after

(Emerson

each

The

and

detector

to the

by applying

a

assumption

of global

foreground

removal,

brightness

at that

comparison

adjustments.

destriper global

sky

and

destriper

zodiacal

a similar

baseline

local

the

first

was accomplished

after

estimate

on

foreground The

to match

This

measurements,

destriper,

RMS

points

attempted

wavelength.

zodiacal

destripers.

was

This

able

destriping.

point.

of each

The

detector

destriper

used

to accomplish

The

two

about

destripers

are

Signal

noise

noise

from

Known

Asteroid

Known

asteroids

removed

from

contributor

in the

the

images need

improves

to further

reconstruction

ISSA

on board due

ISSA

images

Information

the

sampling

smooth

the

interval

by 25% over

time-ordered

data.

for the

IRAS

survey

contribute

slightly

(§III.A.1).

listed

HCON

IRAS

satellite

to high-energy

spikes

Removal

data

the

images

attempted

protons

remained

in the

and

to remove

electrons.

SkyFlux

from

However,

images.

the

IRAS

many

small

A deglitcher

removed

(§III.A.3). from

in the

prior

of nonconfirming

individual

the

of Spatial

Removal

of large

the

ISSA

pointing

spikes

vestiges

Representation

obviates

Radiation

data

in the

in the

processing

and

the

Information

resolution

Particle

detector

and

Pointing

to improved

in the

destriper

12.5 ° field.

spacing

images

Improved

A.7

local

to Improve

Improvements

this

global

sky is the

as the

two

at 1.2 million

to every

in cross-scan

pixel

SkyFlux

spikes

the

residual

with

in §III.C.3.

The

A.6

data

of all IRAS

of all detectors

reduction

reduced

in the same

in a single

Oversampling

A.5

the

fluctuations,

was

correction

known

data

described

the

point

average the

point,

the average

destriper,

baseline

survey

detectors

baseline

is that

Baselines

variations

all of the

Griives

second

to residual

responsivity compared

slowly

Detector

the IRAS

to making sources

Coadded Asteroid the

Images and

co-added

(§III.C.4)

images.

II -2

in the

Comet images. co-added

Survey This images.

(Matson

1986)

eliminated Asteroids

were

a major remain

A.8

Full-Sized When

Detectors

flux measurements

by undersized

detectors

sociated

combining

with

are converted

appear

too

different

to surface

bright.

Thus,

detector

sizes,

(Table II.A.1) were used in making as well as full-sized detectors.

the

ISSA

Table Detectors

Wavelength

B.

the

operative,

The

SkyFlux

in IRAS

Sky

Survey

Atlas

Detectors 29

30

48

49

50

51

52

25

16

18

19

21

22

40

41

42

43

44

45

60

08

09

10

13

14

15

32

33

34

35

37

100

01

02

03

04

05

06

07

56

57

58

59

was

set

Source

Calibration

brightness source

process

scale

of the

IRAS

of the

detectors

12 #m

calibration

presented

to the IRAS

IRAS

by Rieke

were

used

source

survey

in a three-step

detectors

et al. (1984)

Frequency

As mentioned

response

across to the

point

long

flashes,

exposure term

source

(DC)

calibration

source

calibration

was

maintenance VI of the Main

of the

model

were

detectors

made

and

for

to the

ground-

of c_ Tau.

This

No

changes

have

been

ISSA. standard,

of the

point

NGC6543, source

Supplement.

between are

tied

First,

The extrapolation from of asteroids. Details of

Supplement.

to a secondary

in Chapter

internal

calibration.

A model

internal

detailed

and

Details

was used

stimulators.

to track

A number

of

in §III.A.2.

Response the

which

a detector

in Chapter

Longer and

61

process.

via measurements

Main

for short-term

above,

stimulators,

VI of the

transferred

responsivity to this

as discussed

point

then

are found

improvements

scanning

in Chapter

absolute was

of this process

internal

60

Method

calibration

absolute

are

Spatial

53

of Calibration

stimulators

B.2

_-sized

Images

28

point

as-

detectors

used

25

Calibration

the

images

24

10 #m

made

problems

II.A.1

calibration was extrapolated to 25 and 60 #m using stellar models. 60 to 100 #m was based on observations and model calculations this

measured

full-sized

23

point

based

photometric

the

images.

sources

12

Point The

point

to eliminate only

(#m)

Overview

B.1

Used

brightness,

IRAS

flashed

at the

survey

VI of the thus

Main

accurately

to point

sources

responsivity was

detector

were

needed

responsivities

for

a duration

rate.

These

Supplement. calibrating revealed

of the

II - 3

flashes

to the

a difference

by

point

that

photometry.

the

of a point

calibrated

were

between

suggesting source

monitored to that

were

All data data

detectors,

for extended

were similar

scaled

to the

frequency.

short

term

a correction This

of

to NGC6543 relative

source the

use

source

correction

(AC) to

the was

obtained by measuring detector responseas a function of dwell time during the IRAS mission in an attempt to define the frequency responseof the IRAS detectors. Point sources were scanned across the detectors at 2, 1 4, 1 s1 and _ of the survey scan rate. Measurementswere extended to longer periods, with flashesof the internal stimulators lasting tens of secondsfor 12 and 25 #m and by extended stares at point sourcesfor 60 and 100 #m. Some of these measurementsare shown in Figures II.B.l(a)-(c), which is reproducedfrom Figure IV.A.4 of the Main Supplement. The temporal response shown in Figures II.B.l(a)-(c) is translated scan rate of 3.85 _ s -1 . No attempt data.

was

Instead,

in order 25 #m

the

to best and

60 and of these

factors

Suggested

surface

100 #m).

brightness

should spatial

corrections

can

to the be

for 12 and

total

25 #m

Correction Between

sistent

measurement

was

suggest a nonlinearity on brightness. The long

wavelengths

sources

at 60 #m

and

12 and

0.92

The 25 #m

in Table

ISSA

in each 2 ° at

and

1.00 DC

band 12 and

at 12, 25, calibrated.

sources),

the

correction from

survey

for the

(>

therefore

(point

inverse

factors

Figure

for

II.B.l(a).

II.B.1.

II.B.1 for

2 ° at

Spatial

12 and

Frequencies

25

pm

(deg)

12/_m

25 #m

0.1

1.15

1.10

0.2

1.18

1.13

0.5

1.25

1.18

1.0

1.28

1.20

1.5

1.28

1.23

2.0

1.28

1.23

Scale

factors

photometry

response

of the

obtained

for

the

detectors

60

in photometric 100 #m,

to recover

from

which makes the uncertainty in the

results

are

Factors*

scale frequency

0.82,

scales

IRAS

factor

scales

measured.

for

Factors

* Multiplication

the

0.78,

Multiplication Spatial

While

flux

are found

6 r and

spatial

products spatial

determined

Table Suggested

were

ZOHF

the

correction

by a single

at large

factors the

using

response

multiplied

on the smallest

be applied scales

was

and

response

frequency

brightness The

ISSA

frequency

a true

calibration

the

respectively. correct

a spatial

to perform

source

> 5 ° at 60 and the

intermediate

point represent

100 #m,

To recover

made

into

and

100

small-

ISSA at #m.

data.

12 and

25 #m

Figures

was

II.B.l(b)

clear, and

no

con-

II.B.l(c)

frequency response at 60 and 100 #m dependent overall linearity of the photometric scale at the uncertainties

respectively. II - 4

of about

30_

and

60_

for extended

SPATIALSCALE(degrees) 0.5

0.10.2 I

I

1.0

I

1.5

I

1.3

ASSUMED

I

DC/SURVEY

RATE

RESPONSE

rl A ¢_z

1.2

n

1.1

tu ev

1.0

,

I 10

0

i

DWELL •

1/2 SURVEY

13 STARING

RATE

J 20

TIME

CALIB

OBSERVATION

3O

(seconds)

OBS

aLYR

aLYR

DET

DET

29

29

•

1, 1/2, 1/4, 1/8, 1/16 SURVEY RATE CALIB MEAN OF ALL SOURCES DET 53 aLYR

OBS

&

REFERENCE

FLASH-MEAN

SOURCE

OF COLOR

BAND

LONG

DURATION

NORMALIZED

AT 3.2 sec

SPATIALSCALE(degrees) 0.10.2 1.3

I

0.5

1.0

I

I

ASSUMED z

1.5

]

1.2

I

DC/SURVEY

RATE

RESPONSE

& A

z_

2'"

1.1 -0

25 _m ,

1.¢

I 10

0

J

DWELL •

&

1, 1/2, 1/4, 1/8, 1/16

SURVEY

FLORA,

45

aLYR

REFERENCE OF COLOR

Figure

II.B.l(a)

dependence ments

were

by viewing translated scan

of the

rate

made

DET

SOURCE BAND

Measurements detectors either

by

of the

CALIB

DURATION

OBS

FLASH-MEAN

AT 3.2 sec

response

panel)

a source

long flashes of the internal the dwell time of the lower of 3.85'

LONG

3O

(seconds)

RATE

NORMALIZED

at 12 (top crossing

TIME

I 20

and

vs. dwell

time

25 (bottom

at scan

rates

to measure

panel) less

than

#m. the

frequency

The

measure-

survey

rates

or

reference source. The upper horizontal scale has scale to spatial frequency using the IRAS survey

s -1 . II

5

SPATIAL SCALE (degrees) 0.51.0 II

_

2.0

5.0

I

I

8.0

1.4 ASSUMED 1.0 rl

DC/SURVEY

RATE RESPONSE

o

o

o

ALPHA LYRAE

O

0.8

J 2O

0

I 40

I 60

I 80

I 100

120

DWELL TIME (seconds) SPATIAL SCALE (degrees) 0.5 1.0 I

w

1.4

0

1.2

2.0

5,0

I

I

I

&

f,oLU

8.0

o

[]

,.°

n"

NGC 6543

0.8

I 20

0

I 40

I 60

I 80

,I , 100

120

DWELL TIME (seconds) SPATIAL SCALE (degrees) 2.0 5.0

0.5 1.0 I

_uJ _co rr z _O

I

I

1.4 [] 1.2

_0tll Za:

1.1>

er

0,8

8.0

I

[]

I

[]

[]

IRC + 10216 I 20

0

I 40

I 60

I 80

I 100

120

DWELL TIME (seconds) 60 gm O SURVEY RATE OBS DET 14 •

1, 1/2, 1/4, 1/8, 1/16 SURVEY RATE DET37

•

1/2 SURVEY

RATE CALIB OBS DET 37

•

1/8 SURVEY

RATE DEE 14

[]

STARING OBS DET 14

A STARING OBS DET 37 o

Figure

II.B.l(b)

dependence

at scan

reference

source.

scale

Measurements

of the

a source

to spatial

1/2 SURVEY RATE OBS DET 14

detectors

rates

at 60 #m.

less than

The frequency

of the

upper using

the the

The

survey

horizontal IRAS

response

vs. dwell

measurements rates

scale

were

or by viewing has

survey II - 6

translated scan

rate

time

to measure

made

long the

of 3.85'

either

flashes

dwell s -1.

time

frequency by

crossing

of the

internal

of the

lower

SPATIAL 1.0 1.4

_0 z o3o.

SCALE

3.0

I

(degrees)

5.0

t

8.0

1

I

1.2

Lrl_

ASSUMED DC/SURVEY .._.I:;L_ ..C] w ..J3 m u

....C]n

RATE

RESPONSE

Ow 09 uJ a:

ALPHA 0.@

I 20

I 40

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Figure

II.B.l(c)

dependence a source reference scale

to spatial

1 SURVEY

•

1/2 SURVEY

RATE RATE

OBS

DET

6

•

1/8 SURVEY

RATE

OBS

DET

6

n

STARING

OBS

Measurements

of the at scan source.

•

detectors

OBS

DET

DET

6

6

of the

at 100 #m.

response

The

vs. dwell

measurements

time were

to measure made

either

frequency by crossing

rates less than the survey rates or by viewing long flashes of the internal The upper horizontal scale has translated the dwell time of the lower frequency

using

the

IRAS

survey II - 7

scan

rate

of 3.85 _ s -1.

B.3

Detector

Effective

After

data

tronics the

were

as discussed

average

solid are

the

surface

angle

values

discussed

Zero The

of sky

the

brightness

over

zero

free

point

from

the

each

difference

of the

The

the value

observed

position

of the

of the

source 0.2%

assumed B.5

was

this

The

in 1986

and

Survey.

The

not

intended

to provide

are found

in §III.A.2.

As discussed

in §II.B.2,

in the 100/tm

Suggested

for the

electrical

offset

used

IRAS

secondary

CS-15.

The

total

signal

TFPR

(§III.A.2.b)

and

signal

was

for correction

zero

slightly

point

ascribed

of the

is dependent

position

of/3

throughout

NGC6543

at/3

in the

in flux among 100 #m,

Extended was

of the

ISSA

to an area

(the

to the

zero

point

in

on the

accuracy

= 89.2 ° and

_ = 94.6 °

the

mission.

However, the actual

The

observed

/3 = 89.2 °, A = 95.0 °

= 89.8 °, A = 150.3 °. NGC6543 transfer

standard

derived the

offsets,

TFPR

respectively,

(Main it is not

locations of the

considered

is roughly

absolute

was

Supplement a

0.03%,

zero

point

as

§III.A.2.b.

calibration

variation

predicted

discrepancies

for

are

in §II.B.2.

The

Source

NGC6543

observation model

as a secondary

variation

Limitations point

past

model,

annual

Features

to yield

release

by reference

and

/3 = 88.8 °, A = 268.9 ° and

at 12, 25, 60 and

TFPR

maintained pole

on a TFPR

varied

between

caused

the

5 ° at 60 and

Faint

used

§IV.A.3).

latitude and ecliptic longitude, respectively. CS-15 calibration observations were executed,

calibration

and

cies.

SkyFlux

to the

calibration

of the

based

direction

1.9%

Calibration

model

was

elec-

(§III.A.2.b).

TFPR

source

of error. and

zero

detector

their

by linear interpolation between offsets obtained during This process is described in more detail in §VI.B.3 of

derived

varied

scan

point

by the

The

and

which was accessible throughout the entire Flux Photometric Reference or TFPR. The

brightness

and

accuracy

as the

Although

0.5%,

detectors

Supplement

the

ecliptic

electronic

prediction

TFPR

on the

major

special

measured

The

model

position

§VI.B).

since

was set and north

to the

was obtained of the TFPR.

brightness

in the

(Main

Supplement

the

the

where /3 and _ represent ecliptic due to the method by which the

used

of each

of view

improved

calibration near

using

The

TFPR

depending

angle

of the

in §III.A.2.c.

compared

between

Supplement.

TFPR

IRAS

daily was

offset.

Main

have

Explanatory

sources

survey observations these measurements the

solid

field

Main Supplement §VI.B), area was called the Total

detector

electronic

ISSA

the

is given

of the

point

was observed

from

effective

response

Calibration

calibration standard IRAS mission. This TFPR

for

of the

difference

Point

for frequency

in §II.B.2, used

of the

Angles

corrected

in §II.D.2

magnitude B.4

Solid

Sources

severely

TFPR.

limited

This

is not

accurate

absolute

the

scan

with

appear correction

too

IRAS spatial faint. factors

The

were

less than correction

for intermediate

II-

knowledge problem

photometry.

data

scales

by our a major

8

not

of the since

the

Uncertainties

corrected

spatial

25 #m

flux

ISSA

images

for the

TFPR

for all spatial

2 ° at 12 and factors

absolute

and

for point

sources

scales

are found

frequenless than are

given

in Table

II.B.1. Large uncertainties, 30% and 60% at 60 and 100 #m, respectively, exist in the factors for spatial scalecorrections. This uncertainty in the frequencyresponseof IRAS at long wavelengthsis the major sourceof uncertainties in the absolute calibration of ISSA. The user is directed to a careful reading of §II.B.2 and examination of Figures II.B.l(b) and (c) before attempting to perform photometric corrections for spatial scalesat 60 and I00 #m. C.

Product

Description

ISSA, Flexible

combined Image

along

varies

in Figures

SkyFlux fields. field centers. For image

for

image and

of all

The

small

FITS

that

any

number The

and

upon

noise

size of each

ISSA

range The

(12,

standard

range

deviation down

down

16 bits

The

through: Request

to that

requires

image

Reject

MD

the

there

images

fields

spacing

equatorial

with

HCON-3)

deviation

Set

and

User

mean

threshold per

pole

from

the

corresponding

is an plus

were

about

Support

20771.

II - 9

The

intensity

a co-added

also

number

comparing of each noise

produced

is used.

of bits

per

it to 5% of median

pixel. level,

If 16 bits

then

the

is too

number

In FITS-formatted

of

images,

sample.

0.5 or 1.0 Mbytes,

set of ISSA

comprises

sample.

and

5% of median

32 bits

is either

entire

range

of the

to the

633.4

Greenbelt,

Set

in

consists

is different

100 #m), and

16 or 32 bits per

the intensity

NASA/GSFC Code

Reject

25, 60 and HCON-2

ascension,

at the south scheme

ISSA

image

size of 1.5 t. The

In right starts

numbering and

(HCON-1,

standard

of signal.

is available Coordinated

ISSA

are either

intensity

ISSA

the

Each

a pixel

images

at IPAC.

images

than

10 ° apart.

that

and

et al. 1981).

numbering

entire

Coverage

information

greater

dynamic

4.2 Gbytes.

the

by examining

is the

will carry

Note

wavelength

request

intensity

(Wells

of sky with

spaced Field

coverage

intensity

to hold the

bits

IRAS

coverages.

was determined where

II.C.3.

confirming

the

is a set of 430 machine-readable

format

are

poles.

A lists

and

are available

sample noise,

each

which

II.C.1

field

Set,

(FITS)

at the

Appendix

each

Reject

a 12.5 ° x 12.5 ° field

bands

to convergence

as shown

ISSA

System

covering

declination

due

the

Transport

of 500 x 500 pixels are

with

plus

ISSA

depending Reject

1.4 Gbytes.

Office

(CRUSO)

images

on noise has

level

a size of

/

/,

/ t
5. Most

due

Faint

Events

the

re-ordered based on sky position. All scans one database called an ISSA field. A field IRAS

The

Image

SNR

Position-Ordered

reprocessing

into segments were grouped

C.

with

than

compressing.

were

for the

IRAS

data

> 5).

priately to signal downstream processors that deglitching data were used in creating the ISSA images. The deglitch of the

and

detector

threshold

interpolation

Even

typically

§II.C.2.a).

of five (SNR

frequency

a quality

for the

to phasing

by a factor

linear

used

Survey,

over

were

hits. of less

§IV.A.6).

as that

Source

of radiation

an amplitude

artifacts

Supplement

Faint

source

with

These

same

data

noise point

data.

is the

of a high-pass

the

artifacts

(Main

to the

detector

greater

by the removal

many

in the

detector

output

improved

detectors

by the

time-ordered

the

a frequency

remained

Supplement

monitored

were

deglitcher,

the

used

(Explanatory

cessor that

noise

impacting

deglitcher

operated

data

an onboard

sample

particles

The

detector

used

striping RMS of

detectors corrections

did

were not applied to these detectors. No corrections wereavailable for 20% of the survey scansdue to constraints in the empirical procedure. C.2. bands.

Zodiacal

Foregrottnd

Removal

Zodiacal dust emission is a prominent source of diffuse emission in all IRAS survey The apparent dust temperature of about 250 K makes the zodiacal emission most

prominent

in the

ecliptic

plane.

amount with

12 and

The

25 tl.nl bands.

zodiacal

contribution

of interplanetary the

Earth's

The

dust

position

the

the

discontinuities

different

times.

the

concentration

the

sky

model

and

These

artificial

useful

subtracted

it possible

spatial

from

model

a consistent

models

The

model

properties

of the

sylnmetry

plane

of wavelength. integration

dust. with The

of dust

data

zodiacal zodiacal difficulty

They

predicted

due

such

emission

that

Users wishing to know the total may do so by using the ZOHF Zodiacal

pole

emission

at 12 and

25/ml.

subtraction The

of a

at

associated faint

with

features

A zodiacal

on

emission

emission

on the radiative

use

the

and

at large

solar

of IRAS

cloud

for direction

where angles.

and the

density,

the

allowed

radiative

tilt of the

dust

(lust

as a function

time

was

obtained

model

dust

cloud.

by The

to a selected set of II1AS scans. Because that (lid not include the zodiacal dust

data.

95% of the total

zodiacal

at such

of the and

through

zodiacal

model

elongations

data

distribution

emissivity

properties

large-scale

of a physical

sky brightness in a particular Version 3.1 (§I.F).

removed

residual

brightness

zodiacal

to estimate

as dust and

line-of-sight

in the

based

the dust

plane

zodiacal

IRAS

difficult.

foreground

paucity

to describe features

remain

gradients

for scans

bands,

bands

the

used

to the

were determined by fitting the model assumed a physical dust distribution dust

varies

of sky were observed obscured

G. The

parameters the model the

on the

which

sky

plane,

emission was

ecliptic

along

the

natural

HCONs

to reduce

dust

zodiacal

emission

several

emission

include to the

depends

an amount

the

emission.

parameters

respect

brightness

patches

ecliptic

in Appendix

have

fourteen

the

foreground

of the

would used

ISSA

adjacent

as well as the

of the

in detail

prediction

empirical

where

remaining

of the

It is described

Consequently,

toward

of the zodiacal

distribution

emission.

the the

cloud.

toward

by IRAS, changes with time as the Earth moves of the variable zodiacal emission was to introduce

gradients, emission

surface

line-of-sight,

images

co-addition

to co-add

A physical and

SkyFlux

of zodiacal

made

was

make

in the

is concentrated

particular

dust

particular location on the sky, as observed along its orbit around the Sun. The effect step

distribution

to the observed

along

within

dust

emission

seen

region

brightness at the

as observed

at the north

north

ecliptic

by

ecliptic

pole

at 12

and 25 #m shows variations of 0.5 MJy sr -1 and 1.0 MJy sr -1 , respectively. This appears in the ISSA images as a "bow-tie" at the pole. At intermediate latitudes this variation in residual lower

foreground amplitude

to 1.0 MJy

sr -1

appears than and

the

as low-frequency polar

2.0 MJy

bow-tie sr -1

(greater

(0.2

at 12 and

III

MJy

than sr -1 at

25 l,m

11

5 ° period) 12 #m).

for fields

near

striping The the

of somewhat

residuals ecliptic

increase plane.

C.3

Destriping Due

to

imperfections

stripes remained to in-scan RMS three,

and

RMS

1.5 and noise

detector-to-detector

be

to derive

destripe

offset

computed

from

The

two algorithms

not

three

only

assisted

additional

the position-ordered, cross-scan RMS noise The ratio

noise,

Each

detector No gain

The found

of the

Overview

following

is a brief

assumption

when

pointed

zodiacal

that

each

detector

at the

same

spot

of many

A typical

hundreds

during tile mission. each detector scan. adjusted was

There issues

until were

related

the

zodiacal

size

of the were

database size of the

of the

the

of the

global

scan

in the

incoming

hysteresis

removal.

database size ranged database

needed focal between affected

and

destriper.

The

but

This

also

allows were

cor-

brought

mosaicking derived

from

cross-scan

the

striping

A detailed

1988).

should the

a single wavelength

scan

can be

a BasketWeave

algorithm

was

see the

same

mission

same

that

(§IV.E.1).

description using

This

original

such

1.0 for all bands

accomplished

in implementing datastream One

a global

crossings.

After

470 megabytes fitting

an

the

during

the

involved

to support plane

with

after

based intensity

removal

observation taken

on

of the

crosses at other

the times

difference history for Each scan was then

and

the

fit. The

process

minimized.

of difficulties

1.2 million

local

crossing

The local destriper reduced by an additional 10%.

during

path

between

a number and

level.

wavelength

of the

to anomalies emission

applied.

possible to generate an intensity data were fit with a polynomial. were

from

were the

the

to remove

corrected

parameters

destriper.

Gr£ves

same

detectors

to have

was

striping

is nearly

was

sky anytime

difference

differences

the

regions

and

was

methods

information

and

destripe

of ISSA

detector

of other

It was therefore The difference

by a portion

repeated

of the

in the

destriper

reduced

(Emerson

two

scan

background

local

in flat

destriping

(BWDS)

emission.

paths

overview

D. Global

algorithm

noise

of ISSA

corrections

detector data. global destriping

methods

Destriper

in Appendix

DeStriping

two RMS

the ratio of cross-scan #m is between two and

detector-to-detector

The

detector-to-detector

time-ordered, zodiacal-emission-removed detector within a scan. The global

to a common

adjustments.

to in-scan

Global

the

used

of each

to as the global

globally-corrected as measured after

combination

of cross-scan C.3.a

there

a goal

RMS

parameters.

(HCONs)

offset

destriping, 12 and 25

Since

Each

in decreasing

models,

in-scan

implemented.

are referred

sky coverages

without

the

were

derived

zodiacal

100 #m.

to the

destriper utilized the entire IRAS survey to derive destripe parameters for each

rections the

2.0 at 60 and

parameters. the

and

data. Without of the sky at

equivalent

variations

scans

global dataset

calibration

in the IRAS detector noise in a flat region

between

cross-scan

in the

major

III - 12

this approach, as

the

consideration

basketweaver. careful

for 25 #m

checking

as well

selection

Over

was the

(Appendix

to 730 megabytes

strategies.

including

completeness the

of

enormous

entire

mission,

D) the

final

at 12 #m.

The

Intensity differencefits wereperformed for eachscanat eachwavelengthusing at most tenth order orthogonal polynomials. The fit technique and order varied to someextent with wavelength. Intensity differenceplots provided good visibility as to the quality of the fit. However, due to the volume of data, comprehensivemanual checkingusing plots alone was not feasible. A computer program analyzedthe fits for eachdetector within eachscan, producing a set of parameters. These parameters servedto indicate possiblefitting problems. Histograms were generatedfor eachparameter and the fits which produced extreme outliers wereinvestigated. Identified problems were either fixed or removed (Appendix D). C.3.b. The rithm.

Local

local Each

De_triper

destriper detector

algorithm of the

was

same

the

field.

local

destriper

region.

The

by the

global

Input

the global utilized

local

A co-added

Then

the

were

taken

The

image

trajectory

of the

between

the

see the

from

utilized

all focal

in further

same

a subset plane

reducing

was position-ordered, process

was

assumption

as the

intensity

global when

made

detector

local

of all scan

segments

values

of focal

crossings the

plane

crossings,

within

cross-scan

the

RMS

the

dcstripe

parameters

within

a defined

co-added

image

was

detector

along

the

of the

determined. scan

and

Differences

co-added

process

iterations

of the

iteration

the lower frequency image to prevent

influencing

An error

image

to 1.5' for the final.

helped in reducing from the co-added thereby

co-added

the

in the

detector

local

image

scan

destriper

was

were

Starting

made with

quality

software Due scans, destriper

checking was fixed

the

to the fields from

process,

differences software

(§III.D).

for processing

residual covering the

fields

the

Some

1/31
Reject

III.D.l(b). Table

Amount

consisted

a somewhat

the inspections quality check. of data

20 ° sky is shown Set

faint

consistency

Johnson, performed this post-production

during

of energetic particles. As mentioned The tail of comet Iras-Araki-Alcock

appeared

maintain

The

found

of Data

III.D.l(a)

Removed

Wavelength

in Anomaly

% Data

Processing

Removed

(I/3] > 20 °)

% Data

Removed

(1 1 > 50°)

(1 I < 50°)

12

0.18

0.51

25

0.30

0.31

60

0.14

0.24

100

0.07

0.26

Table Amount

of Data

III.D.l(b)

Removed ISSA

in Anomaly

Reject

Set

of the

(]/_[ < 20 °)

% Data

Wavelength

Processing

Removed

(#m)

D.4

Types An

are

described

tion

process

except

those

0.34

25

0.30

6O

O.27

100

0.47

of Anomalie_

attempt

Anomalies

12

fell

was into below.

described that

made

two

to

main

Most

characterize groups,

of these

in §III.D.3.

caused

the

data

the

anomalies

anomalies

anomalies

were

All processing

improper

handling III - 22

found

and

processing

removed

problems of saturated

by

through

were data.

corrected

visual

inspection.

anomalies, the

which

visual

inspec-

in the

software

D.4.a

Data

Anomalie._

Focal

Plane

and

All or a subset time

then

fairly

fell

sharp.

Partial

of the

back

Focal

detectors

in the

to approximately

This

was

likely

Plane

focal

their

due

Anomalies plane

original

to either

Detector

to a higher

intensity.

a particle

the telescope or by a shower of secondary energetic Figure III.D.1 shows the distribution of focal plane --

jumped

Both

or paint

the

flake

particles from anomalies.

the

intensity

rise

problems.

Processing

--

The

distribution

of detector

Local

These

191>

structure.

streaks

and

Generally streaks

ministreaks

the were

is found

Anomalie_

Destriper

anomalies

were

shown

to appear

only

were caused by an error in the local destriper in the time-ordered detector data. A number prior

of

III.D.2.

D.4.b

images

were

field

Streaks/Ministreaks

to calibration

in Figure

fall

near

observing

One or a few detectors showed nonconfirming spikes or raised intensity. mini-streaks were due to orbital debris in the field of view, whereas detector due

and

in the

for a

because

they

were

not

bright

enough

to processing the 1/31 < 50 ° sky. 50 ° sky is found in Figure III.D.3. Saturated

An

error

was

Detector found

after

to stand

intensity

nonsaturated

intensity

in the Galactic a list of fields occurrences

values.

algorithm

for

in making

the

Figure

III.D.4

plane where 60 and along with the number

throughout

the

destriper

processing.

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This

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was

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for

the

Data

in the

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Distribution

handling

error affected the SkyFlux inmges as well as the eliminated the wrong detector when saturation of saturated

the

software that did not account for data gaps of local destriper anomalies were left in these

mission

saturated

intensity

saturation. There may be several detectors that on an average ten detectors saturate about < 0.005% of the survey data.

images shows

Each

saturated per second,

III

This

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erroneously the

problem

100 pm detectors saturate. Table of occurrences in each field. The is 6,289.

values.

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III.D.2 provides total number of a single

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387

18

12

170

338

32

194

171

103

33

289

182

22

34

24

* 183

22

35

30

189

278

36

76

* 190

278

37

57

206

436

52

113

2O7

196

58

17

226

136

59

369

227

14

6O

119

248

12

77

32

* 249

12

78

27

262

8

86

37

263

163

87

448

104 * 105

*

III.D.2

284

10

8

297

77

8

298

115

117

374

331

2

118

1603

360

6

119

30

361

4

137

8

390

9

* 138

8

391

59

152

27

407

6

Overlapping

area

with

adjacent

III - 27

field

not

included

in total.

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+

+

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+

\

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III

28

IV.

A.

Analysis

RESULTS

Overview

Analysis the

ANALYSIS

of the IRAS

quality

of the

sky, released

ISSA

in 1991.

Sky Survey

images. The

Atlas

The

analysis

was designed

analysis

is mainly

concentrated

to verify confined

on the position

accuracy,

sistency, spatial resolution and noise of the Atlas. The results to the entire ISSA data set, which covers the I_l > 20° sky. covering

the

Reject

l/_l < 20 ° sky is of reduced

Set.

plane

The

and

the

reduction

zodiacal

bands.

of ISSA

is 4.5'

are photometrically uncertainty was

used

is due

to the

surface brightness to-detector offsets in the the

ISSA

noise

B.

accuracy

Point 30 °,

Point

source data

spatial shifts

to have

small

source

at

12 and

ecliptic

for these

images,

§IV.F.

sources

show

Catalog

within

that

to within

the

data

10%.

This

tim convolution (Appendix

filter B).

that

Relative

The effects of detectorso that the noise level

is approximately

photometric

brightness

23 sources at 60 and a large

25 #m

that

expected

from

consistency

between

are listed

were

5 and

selected

55 Jy

and

to be correlation

were studied enough emission at

high

using

to measure or nearby Galactic

coefficients

point easily point

latitude, of 0.99

or

at 12 pm and 24 sources at 25 gm are listed in Table IV.B.1. 100 #m were selected from the IRAS galaxy list (Soifer et al.,

radial

velocity

Jy. The velocity criterion is designed be extended at the resolution of the at 100 pm

ISSA

at the

to 2' samples

sky

product,

emission

scales is possible. have been reduced

latitude

are applicable set of images

to within the limitations of than 0.1 pixel. The spatial

point

Source

con-

detectors.

and

sources

with

greater. The Point sources 1987)

accurate to better

IRAS

high-ecliptic

IRAS

images are accurately

selected from the IRAS Point Source Catalog to be bright ISSA data and to be free of interference from extended

sources. Ibl >

in the

is presented

of a point

over large emission

a separate

zodiacal

analysis

IRAS

analyze

photometric

reported here The remaining

considered

of ISSA

and

Accuracy

Positional sources in the

the

resolution

photometry and zodiacal

images

Positional

with

fldl

and

to residual

Measurement

positioning

the

in individual

the ISSA positioned

to 5'.

consistent

to resample

is due

A separate

The analysis results sllow that the IRAS data. ISSA data are resolution

quality

in quality

the accuracy

to the high-ecliptic-latitude

in Table

(>

4000

km

s -1)

with

brightness

between

5 and

55

to select small angular diameter galaxies unlikely to ISSA maps. The 14 sources at 60 #m and 15 sources

IV.B.1.

IV

1

o

=

_

_

_

_

_

_

_

_

_I

_

0

_I

N

N

o o Z

I

I

I

I

I ____

° ,,.._

_o

¢) V o

°_-_

0

I

I

I

I

I

I

I

I

I

I

I +++++++++++ co

E_

IV

- 2

The

position

selected

sources

Source

in the

Catalog.

ISSA

map.

The

over

Figures

IV.B.I(a)

the ISSA

obtained are than

analysis

ISSA ISSA

Photocenters

positions and

accuracy

and

less than

the

region

(9")

published

taken

and

a source

point mean

the

expected

PSC

of a single

and

ISSA

source

is less

point

spread

Statistics

25 #m

60 #m

100 #m

23

24 0.001

0.040

0.031

a(A R.A.)(') Mean A Dec.

(')

0.156 0.070

0.267 0.034

0.179 -0.078

0.224 -0.131

0.126

0.225

0.156

0.236

Dec.)(')

selected

point

sources

function

of 1.5' period

of interpolated there is some the

(see

widths which

apodized

with

§IV.B)

were

used

to study

the

a cosine

to a full width

of 12 zero

ISSA

point sources spacing using crossings.

point spread functions are shown in Figures IV.C.I(a) noncircularity evident. The short axes of the PSFs, when scan

the point spread functions indicate that the resolution

in both of the

algorithm

15

at half maximum (FWHM) of these had been interpolated to 0.15' sample

predominant

axis of the

14

Function

(PSF). The full from ISSA data

binning

position

the statistics

the

0.004

function measured

long

pixel

background. PSC

summarizes

between

uncertainty

the

(')

Spread

with

IV.B.2

Point in the

of the

of a local

A R.A.

a(A

line up

IRAS source

average

between

of the

IV.B.2

Difference

# of Sources Mean

plots that

Table

position

12 #m

The

in the of the

subtraction

differences

position

(18").

Position

Point

after

sources.

Table

C.

locations

photocenter

of difference

position

apparent

a flux-weighted

histograms

The

the

source

to be the

by producing

display

for the selected

of comparing

the

was

surrounding

histograms.

0.1 pixel

0.2 pixel

with

obtained

IV.B.I(b)

position

from

maps position

were

a circular

consisted

image. used

This

spatial

to produce

direction.

Table

IV.C.1

lists

the

the long and short dimensions. ISSA is 4' to 5', depending on resolution the

ISSA

is consistent images.

IV - 3

with

measured

were a sinc

Contour (d). Note discernible, FWHMs

of

These measurements the orientation of the

expectations

based

on the

' 4.0-- MEAN

I

'

I

'

= .070

n

POP = .126

II

SIGMA - SIGMA

MEAN

I

'

'

4.0

I

'

I

'

i"1

= .034

I

]l ii

SIGMA

= .026 ]1

"SIGMA

3.0

3.O

N

POP = .225 MEAN

t1

= .046 II

= 24

2.0

_2.0

1.0

l°r P lIIt

0.0

4.0 -

-1.0

0.0

12 Bm DELTA

RA (ARCMIN)

'

I

I

MEAN

'

O0

1.0

4.0

= - .078

'

--

0.0

RA (ARCMIN)

' I MEAN=

i

' -.131

SIGMA

POP = .236

MEAN

SIGMA

MEAN

= .042

1.0

25 I.tm DELTA

POP = .156

'

I

'

= .061

N=15

3.0

b-, Z

Z © 2.0

2.0

LAL -1.0

0.0

60 Bm DELTA

Figure

I

,

SIGMA

3.0

0.0

I

SIGMA N=I4

1.0

-1.0

IV.B.I(a)

1.0

-1.0

RA (ARCMIN)

Histograms

0.0

100 Bm DELTA

of Position

IV

Differences

4

in RA Between

1.0

RA (ARCMIN)

PSC

and

ISSA

4.0-

_

-

MEAN

= .004

I] SIGMA

POP=

"7 .156

4.0

j

rl SIGMA MEAN = .032[ N=23

3.0

SIGMA

[

SIGMA MEAN = .054

POP = .267

]

N=24

3.0

0.0

L

I

I

j

- 1.0

0.0

12 I-tm DELTA '

4.0

1

MEAN

DEC

'

I

I

0.0-

(ARCMIN) !

POP = .179 MEAN

I

,

]

i

= .041

,

0.0

25 pm DELTA 4.0

SIGMA

I

- 1.0

= .040

SIGMA

-

1.0

N=14

3.0

EAN L

I

I

1.0

DEC

' I ' I MEAN = .031 SIGMA POP = .224 SIGMA MEAN = .058 N=15

(ARCMIN) '

I

'

_

I

I

3.0

m

Z

b-. Z

© 2.0

_2.0

1.0

I -1.0

0.0

60 pm DELTA

Figure

IV.B.I(b)

0.0

1.0

DEC (ARCMIN)

Histograms

1

1

- 1.0

0.0

100 pm DELTA

of Position

Differences

IV - 5

in DEC

I

1.0

DEC

Between

(ARCMIN)

PSC

and

ISSA

Table Point IRAS

12 #m

25 #m

Spread Name

100 #m

Function

Dimensions

field

flux

FWHM

(JY)

(arcmin) 3.7 × 4.8 3.7 x 4.9

10521+7208

414

35.6

15448+3828

355

37.0

17133+3651

357

48.2

05174-3345

102

27.3

3.6 × 5.3 3.6 x4.7

03040-8013

3

26.2

3.6 x4.7

20427-8243

9

12.6

3.6 x 4.6

3

20.8

4.5 x 4.9 3.6 x 5.3

01452-8026

60 #m

IV.C.1

17329+5359

383

21.4

04330-6307

28

12.1

02238-5947

26

12.1

08354+2555

316

24.3

00163-1039

162

6.9

3.7 x4.2 2.7 × 3.9

04315-0840

169

33.5

3.5 x 4.6

23488+2018

270

17.0

3.2 × 5.2

13183+3423

322

24.4

10565+2448

319

14.3

4.5 x 4.8 4.6 x 5.2

23488+2018

270

21.0

09320+6134

397

20.1

IV - 6

3.5 x 3.9 3.8 x 4.6

5.2 x6.1 4.8 x 5.2

IRAS '

15448+3828

I

2O

Z ×

C)

_3

I

,

,

!

I

i

,

5

10 ISSA

J

15 PIXEL

Figure IV.C.I(a) Contour Plot of Point Spread from 0.0 to 13.6, Interval 0.8 IV - 7

I 20

NUMBER

Function

for a 12/zm

Source,

Contoured

I

IRAS 20427-8243 '

'

I

'

'

I

,

I

_

,

i

I

[

1

15-m

z .d

10-

< r/3

5-m

0 0

5

10 ISSA PIXEL

Figure IV.C.I(b) from 4.0 to 11.6,

Contour Plot Interval 0.4

of Point

Spread

IV - 8

15

NUMBER

Function

for a 25 #m

Source,

Contoured

IRAS 04315-0840

15

Z

10

'

'

'

'

,

,

i

i

I

'

'

'

'

I

J

,

,

J

I

'

'

I

, .--u

'

'

I

'

I

,

m

m


m

cause was gain version of the

and

rejected.

The intensity difference increases the gain errors directly. This option

at the Galactic was investigated

plane could only be handled by fitting (see Appendix E) but, since applying

a gain

correction

the point

calibration,

fitting

investigation

are due Both

gain

errors was

coupled within

would

made

at I00

The

100 #m

the

magnitudes

much

greater.

in the

that

an error have

intensity

DC response

to be addressed

to fit this

region

differences

of each

to get

accurately

and

fits near

the

good

allowed

for

near

detector

at 60 pm.

polynomials plane.

it was not

The good

inverse fits

used.

the

The

gain

Galactic

plane

residual

hysteresis.

Galactic

plane.

intensity

weighting

everywhere

No

except

for

#m fit procedure of the

They

were

low intensity

improvement.

source

the increased in the

with the higher order 1 ° to 2 ° of the Galactic Fits

that

compromise

showed

to two effects:

attempt

D.4.d

would

was

similar

intensity

so large

regions.

to the

differences

that

even

60 pm

near

fits up

Letting [P represent the path (W) is defined as follows:

worked

intensity

and

Galactic

to tenth

Inverse-intensity-squared

Inverse-intensity-cubed

procedure

the

order

better

I x the

crossing

and

the

at

caused

weighting

even

with plane

fitting

resulted was

were

problems

in considerable

adopted

intensity,

exception

100 #m

the

for

100 pro.

weighting

factor

I max = MAX(IIPI, IlXl) I ba_ = 2.5 x 10 -7 Wm-2sr W

The

100

thresholds and

residual

pm

and

= 1/(Irnax/Ibar)

fit

was

(_ settings

hysteresis

done the

made

-1

3

in three same

about

W

W=10

iterations

as at 60 gm. the

10._ with All the

60 lira fit are even D-

14

the

order-of-fit

comments more

table,

regarding

applicable

rejection gain

to the

errors

100 pro.

As with the 60 #m fits, the 100 #m fits should be consideredquestionablewithin 1° to 2° of the Galactic plane. D.5

Monitoring Algorithm

global

performance

RMS

in Table

values

D.4 for each

of reduction

carefully

rather

time required to obtain do another iteration.

time. than the

monitored as a function

The

is reduced

Tile

RMS

RMS

a measured difference

value

after

value. statistics

Table RMS Wavelength 12

of Intensity

(pro)

6O

100

Note:

Items

Intensity visibility feasible was

written

prot)lems.

plots,

a. scan-by-scan to the that

The

computed following

the

last

each

iteration

iteration

This

is because

was

not

as

RMS

process. are but

at each

the

amount

wavelength

the

considerable

significantly

less than

required

a Function

Difference (MJy 0.616

sr -1)

% Reduction 33.4 45.8

3

0.306

50.3

4

[0.2961 1.178

[51.9]

0 1

0.717

39.1

2

0.541

54.1

3

0.476

59.6

4

0.435

63.0

5

[65.7]

0

[0.404] 0.672

1

0.437

35.0

2

0.295

56.1

3

[0.2421 1.785

[64.0]

0 1

1.117

37.4

2

0.900

49.6

3

[0.8111

[54.61

some number

from

of which

extrapolation

have

Comprehensive

proved

D

that most

15

of previous

already

been

checking

of detector/scan

a set of parameters parameters

to

of Iteration

0.334

results

is

computer

0.410

are

The

tabulated

2

basis.

prohit)itive

with

fitting number

1

brackets

difference

on due

within

the

of iteration

D.4

Differences

Iteration 0

25

throughout

differences

wavelength.

is less each

an extrapolated

was

of intensity

shown,

using

combinations. served

useflfl:

as indicators

values.

provided

plots

alone

Instead,

good was

not.

a program

of possible

fitting

1) variance of fit for detector-scan 2) absolute value of fit at eachextreme point 3) absolute value of fit slope midway betweeneachextreme point pair aswell as at each end point 4) absolute value of 2"d derivative of fit at eachextreme point 5) number of points rejected in detector-scan. Histograms weregeneratedfor eachparameter and detector-scanwith extremeparameter valueswritten into the Problem ScanSummary File (PSSF). Detector-scansidentified as anomalousfrom other sources(see Appendix C) were written into the PSSF as well. Tile file was then usedto establish namelists for making large numbers of intensity differenceplots. The plots were manually inspected and the scansactually causing difficulties were identified. For the identified scans,problem type, severity and affected time interval were determined and loaded back into the PSSF. During the fitting processa file of rejected intensity differenceswasgenerated. Using this file, all-sky mapslike the onein Figure D.6 wereplotted to showthe global position of rejects. It wasfound that rejects wereconcentratedin high-intensity regions. The Galactic plane is prominent in all four bands; exceptionally bright areassuch as found in Orion, Cygnus and Ophiuchus also show up. The rejects scattered over the sky are associated with bright point sources.The long strings of rejects are due to problem scanswhich }lad to be corrected or eliminated. Problems identified from the intensity differenceplots weredivided into different types basedon characteristic signatures. The types can be grouped into three categories,which map as follows into two of the three broad anomaly classespreviously discussed(§D.3): 1) problemsintroduced into the data stream prior to BWDS processingthat could distort the BWDS fits (Class IA) 2) problems introduced into the data stream prior to BWDS processingwhich would not distort the BWDS fits (Class IB) 3) time intervals identified when the global BWDS fits shouldnot be usedfor downstream processing(ClassIII). ClassII anomalieswereeliminated prior to fitting. Residualeffectsfrom incompletely removed Class II anomalies were apparently small; none were identified on the intensity difference plots checked. It is possible that some of the scattering attributed to other causesmay have resulted from incompletely removedClassIIs. ClassIA anomalieswhich could be identified beforehandwerealsoeliminated prior to fitting. Pre-fit identification of theseanomaliescamefrom the original imagesaswell as the latest calibration and pointing reconstruction processing. Figure D.7 illustrates a serious ClassIA anomaly. This particular anomaly affectsall detectorsin all bands and is believed to be the result of a paint flake passingin front of the focal plane. If not removed, it would not only distort the fit (solid line in figure) for the observationin which it occurs but could also adverselyaffect the crossingscanfits. This

D - 16

f

f_

f

7"

-_'_ _ @I

©

7_

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I

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-y

°_-._

© O

J /

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z •

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____J

J D - "1.7

°_.-_

© ©

type of anomaly, once but for all downstream Figure moved

identified, processors

D.8

illustrates

hysteresis

as the

anomaly

sometimes side of the

point

point

source,

signature

the

ing and

descending

because

they

the

time

periods

gone

into

dency

too

Class

for the a plate

ference

between

a spatial

help the

intensities

Time

point

Another type of Class III anomaly can occur when there is a large internal there

are

no

crossing

points

of this where

slope

source. negative

the

affect

Had

intensity

An

automated for this type

Second,

those

gap period to provide

type, the

fits

whose

the

fit within

Those

gap

times

with

at the

to maintain

marked

to prevent

points

would

an individual

possible

to the

would

have

there

is a ten-

when

heavily

stressed

an

extreme

the

of intensity sr -1

point

intensity

dif-

difference

were

flagged

for

the

gap,

it is possible not

only

detector-scans detector-scan

for large on the

size

with the powas identified.

an extreme

point

within

the

fit was evaluated at each end of the gap interpolation across the gap. Differences

extreme

points

and

magnitudes

the

greater

linearly

than

interpolated

1.0 MJy

sr -1

only. The one exception to this was in the dual-hemisphere the near-linear assumption does not apply.

relative

photometry

had to remain low. The intent was that or to remove real structure smaller than extreme

bright

figure,

and

0.2 MJy

fits contained

difference-from-linear

were flagged for local destriper overlap region at 25 tin1 where In order

polynomial

Next, the polynomial needed for a linear

between the actual fit values values were computed.

been

be

is illustrated in Figure D.9. This type of problem gap in crossing times within a detector-scan. Since

to constrain

detector-scans

database

techniques,

having

magnitude

exceeded

on

It should

differences

identified

approach was developed to help identify of problem. First, the longest gap in each

were marked. the end points

fit.

it not

ends

of

by the

surrounding

by the

were

type

mix of ascend-

BWDS

the

immediately

the

re-

components

on the

from

excursions to occur within that region. Whether it happens depends of the gap, but also on how stressed the fit is outside the gap.

tential

This

dual-hemisphere

the

database

by incompletely

depends

D.5(a).

BWDS

may also be affected

removed

off near

or finish)

intervals

end

plots

illustrated

to flair

(start

and

scans

and

from As

problems

two saved. or the

order

appreciably

point

positive

in areas

in Figure

anomalies.

potential

not

in the

point

to appreciably

of higher

III

bright

crossing

were

was shown

of an end sr -1

with

the

difference

fits occasionally

locate

MJy

spike

only

It is caused

a very

frequency

that

fit differed

as Class

width

exceeded 14.0 local fit only.

anomalies

anomaly

polynomial

To

within

intensity

These

not

anomaly.

crosses

on the

however,

the

PSSF

IB

Since

a combination

where

the

elsewhere.

III

fit with

scan

crossing.

high

for non-use

Class

up as a double

source

by the user, suspect.

A typical improve

affected

scans.

have

remembered sources are

a typical

shows

either

was flagged as well.

be separated polynomial

across

a plate,

the

it should not be possible 12.5 ° . Order-of-fit criteria

by more

than

fit from

a field width.

having

D -18

rapid

There

fluctuations

frequency

of the

fits

to introduce were selected

artifacts so that

is, of course,

nothing

over

a portion

of

50

'

I

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l

,

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l

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,

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m I

25

¢J Z

0

,-.., -25

Z

-50

Z

,

-75 0

2_

4_

6_

SECONDS Figure

D.7

Intensity

differences

along

a detector-scan

track

illustrating

a

class

IA

class

IB

anomaly. 50

'

I

'

I

'

I

'

I

'

I

'

I

'

I

'

I

'

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'

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:_

25-

g

Z

-50 -

Z -7: 0

, I, I, I, I, I, I, l,l 200 400 600 800 1000 1200 1400 1600

,I

I ,I L'I,

1800 2000

I

2200

2400

illustrating

a

SECONDS Figure anomaly.

D.8

Intensity

differences

along

a detector-scan

D

19

track

50

I

'

1

,

1

'

I

I

I

'

I

J

I

'

I

I

I

'

I

,

I

I

I

_

I

'

I

,

I

'

I

J

I

Z

Z Z

,

200

400

600

800

1000

1200

1400

1

1600

1800

SECONDS Figure D.9 III anomaly. the

scan.

way

The

real

as to introduce

those

fits with

greater the

than

identified In areas

to the

the

scans

artifacts

or remove

real

structure.

In order

point

pairs

point

been

many

close

out

and

global

extreme

pairs,

every

effort some

tion

fitting and

points, every

errors

sky

position.

which plate

slipped

occur

were

global BWDS such effects.

through

By far near

checked

contribution

the

the

which most

ecliptic

manually

were

likely poles.

(§III.D).

to the

image

systematically

place

to happen

against

where

these

there out

and

a

question, differences

legs between D.10.

BWDS

contribution

effects. fit problems

coupled

wrong

for this

subtracted

scan

fits will have

problem fits greater danger

To guard

this

to identify

parameters

problem

In areas was

the global

in such

intensity

of the

made

of indicator

However,

combine

fits in Figure

for adverse was

the screen. We can be confident that the individual BWDS monitoring were not severe in nature. The small

positions

inspected

a class

to address

having

100 #m

point

manually

illustrating

involved

width

for the

checking

scans.

a plate

The

described,

of automated

of indicated

than

are plotted

identified

previously

closer

identified.

pairs

subtracted

method

inspection

track

individual

sr -1 were

has

a detector-scan

the

extreme with

along

is whether

1.0 MJy

was

through

differences

question

extreme

image

As ual

Intensity

with

slipped

slipping is that

through a number

in the

same

is at the dangers,

are many

man-

through

direc-

scan

end

images

scan

manually

the of

ends,

inspected

of the for

References Emerson, IRAS bauer,

D. T.

Catalogs

and and

H. J. Habing,

R. Gr£ve Atlases:

1988,

Explanatory

P. E. Clegg,

and

Astron.

Astrophys.,

Supplement T. J. Chester D - 20

190, 1988, ed.

(Washington,

353. C. A. Beichman, D.C.:GPO).

G. Neuge-

0

°,-_

°,._

_O 0

C_ c_

0

0

0

"3

_n

0

\

D

- 21

APPENDIX Gain

As tensity

discussed

in Appendix

difference

histories.

from

a given

cross

the

detector

path

These

with

of the

the

first

intensity

D, the These

intensity,

suggesting

computed

from

intensity

difference

for

60 and

total

100 #m

emission The

detector, for that

since

near

average

the

gain

data

errors

for each

and

are too large

at these

associated

relative

These

adjustments

were

Detector

01

Gain

Err

Pop.

Sig (%)

The

(%)

02

+11

+01

8.0

analysis

5.1

was

as the mini-survey in Table E.2.

+06

-05

5.5

6.2

repeated

(IRAS

#m

04

03

Gain

08

Gain

Err

Pop.

Sig (%)

These not

(%)

+10

values

a function

3.8

09

10

-02

-09

3.2

3.3

do not of photon

fluctuate exposure

with and

by

percentage

of

broken

that

and

down

the

should

by

intensities be reduced

data.

+02

6.2

of the

1988

57

-01

7.1

14

5.0

Galactic

5.5

IRAS

§III.C.11).

15

32

+13

+08

5.9

58

59

60

61

-01

-20

-05

00

6.1

5.0

7.1

6.9

survey Results

1

are

33

data

known

are tabulated

not

35

38

-03

-23 5.2

4.0

3.4

4.2

3.9

suggests

that

they

to hysteresis.

+09

37

-05

which due

34

+03

3.0

longitude,

therefore E

done

Errors

-06

2.9

was

was

E.2

13

9.2

band

56

a subset

Gain

+02

error

Only intensities considered viable

at 100 #m,

IRAS

+15

5.2

Supplement

+09

This

of

importance to the were converted to

is a small

sign suggests

07

+04

7.8

12

gain

detectors. This was

in the

06

Table

Detector

magnitude

Errors

+11

#m

which

E.1

for 60 /am using

60

band

that the intensities for that detector and should be increased by the given

to the

05

Explanatory

gave more differences

sigmas

detectors

uot applied Table

of in-

intensities

wavelengths.

sign suggests in the band

100

percentage

dust

E. 1. A positive

to other

the

at 100 #m.

zodiacal

population

in Table

by the indicated percentage. A negative are too small relative to other detectors percentage.

average

detector

to the

same

between

from the crossing readily available.

due

plane

as shown

The

use

the

mission.

which, at 100 #m, plane. The intensity

emission

Galactic

the

of the

a correlation

errors.

the intensities removed were

the

were computed detector

gain

makes

by comparing

detectors

during

revealed

differences the Galactic

gain errors using zodiacal foreground

time

(BWDS)

generated

of all other

histories

and

DeStriper

were

at any

differences

percentage with the

BasketWeave

intensities

difference

using the intensity-weighted detector differences near

Errors

histories

detector

E

The

are

values

presentedabove are expected to approximate DC gain errors. To a lesserextent, they may also reflect errors in determination of the detector solid angles. Residual hysteresiseffects werealso noted in all bands. These wererelatively shortlived with time constants roughly of the order of 10 to 20 seconds. References IRAS bauer,

Catalogs

and

H. J. Habing,

Atlases:

Explanatory

P. E. Clegg,

and

Supplement T. J. Chester

E-2

1988, ed. (Washington,

C. A. Beichman, D.C.:GPO).

G. Neuge-

APPENDIX Gain

and

F

Offset

Corrections

F. Boulanger A file containing History

File

presented

(ZOHF)

below

Version versus

3.0

the that

scan

by deriving light

discarding

This

correction

computed

procedure

at high

IR and

that larger the

to the

zodiacal

light

prevented Correction

(30 ° of scan previous and

factors length)

scans

which

have

factors

the root

are

mean

the

average

gain

the

corrections

Table plotted

dispersion F.2

gives

against

is no systematic

too

and

presented

of the

gain

a histogram SOP effect

and

change of the

in the

of low

longer and

F.2.

and

are

close

to one

gain

overall

corrections. with

F-1

which

and

F.l(a) respect

3_

The

the are

by using

only

between

the

in this

at

least

60

the

data.

of the and

These

to elongation

points in the scans

file gives gain

average

and value

At all wavelengths

respectively.

of the gain

The on the

gives

corrections.

data

for short

emission.

zero,

factors the sky,

described

Statistics F.1

region

contribution

were obtained

for each - (c).

elongation.

accuracy.

emission

30 °.

with

which

Galactic

sufficient

Table

offset

calibration

is about

in Figures

the

Galactic

than

These

1988). No correction I correlation across

corrections

gain

the

corrections

for

next.

for which

exists emission

for low Galactic

offset

F.1

with

scans

points

was satisfied

and

times,

corrections,

Galactic

the

three

and

correlation

25 #m

of the

corrections

elongation

for

scans

in Tables

corrections

not

The

emission

in regions

dispersion

offset do

and

80_0 of tile

condition a good

and Pbrault in the IR-H

criteria

no gain

few points

square

This

for each

by all scans

of observations)

of the

between

to match

to the

over data

It was

linear

scan

measured

magnitude

profile

profiles.

iterated

iteration

dataset

light

obtained

of the was

fit is made

at 12 and

only

selection

is

emission

IRAS

was

were

process

day

1988).

Galactic

time

envelope

light

entire

average

and

fitting

where

(Boulanger variations

measured the

for about

that square

were

Therefore,

corrections

and

of the

satisfy

paragraph.

correction offset

subtraction

Zodiacal derived

A zodiacal

corrections

a half

Pbrault

at 60 pm was removed using H I data were derived at 100 #m due to the which

nearest

one

emission.

and

zodiacal

of the

zodiacal

to the

(Ibl _> 25°),

(Boulanger

of the for the

5er from

correction

zodiacal

latitude

IRAS were

1988.

the lower

roughly

if the

axis)

elongation

This

than

compared

the

corrections

P6rault

offset

average

Plan,

only

of the

Galactic

compared

forced

residuals

is valid

on DC

scan.

to match

is negligible

and

and

for that

Observing

H I emission

is negligible

Gain

the

profiles

Earth-Sun

interpolation

scan

a few percent

points

the

with

(Survey

average

dependence

a linear

emission

typically

by linear

accompanies

of how

compute

about

light

offsets,

corrections.

in Boulanger

profiles.

the

DC

on the to

angle

scan

and

A description

used

zodiacal

profile

SOP

Galactic

was

average

force

same

3.0.

described

all points

corrections

gains

statistics

(azimuth

the

consecutive

the

ZOHF

for each

two

zodiacal

with

method

computed

assumed

Version

along

inclination

following was

corrections,

The three

offset figures and

This

shows

root

mean

wavelengths. corrections

show SOP.

that

are there

References Boulanger, F. and M. P6rault 1988, Ap.

J., 330,

Table Statistics

A

Number

( MJy

12

3616

2133

25

3617

60

3384

(3)

Gains

Residuals

sr -1)

( MJy

(5)

(6)

(7)

(8)

0

-0.105

0.482

1.004

0.030

0.114

2132

0

-0.125

0.835

1.001

0.032

0.172

2295

70

0.036

0.403

0.994

0.036

0.162

number

of scans

with

(2)

number

of scans

without

(3)

number

of scans

with

(4)

average

offset

(5)

standard

(6)

average

(7)

standard

(8)

average

a good

fit (correlation

a fit; most a poor

of these

fit (correlation

coefficient are

short

coefficient

larger

than

0.96)

scans smaller

than

0.96)

correction

deviation

of offset

corrections

correction

deviation amplitude

sr -1)

(4)

(1)

gain

Factors

Offsets

(#m) (2)

F.1

of Correction

of Scans

(1)

64.

of gain

corrections

of residuals

(RMS

dispersion)

F-2

after

subtraction

of the

fit

Table Histogram

F.2 of Gains

Number

Range 12 #m 1.045 Total

F-3

12 _m I .5:

I

t

I

7,o_

•

I

I

u

1.5--

1.5

-,,[: ..._... _'..: ,-

,=o

,

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O=E . o•

-15

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•

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J

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-2.5

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] 65

55

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ELONGATION

I 115

-3.5 -50

125

J 50

t 150

I

I

I

-

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I

I

-

Z

.

I

1.04

.96

'"

"° ";'.

:': .#

1.12

-;_

.

I 65

_" :

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ELONGATION

F.l(a)

Gain

I

I

!

•

t.

". -_.

_.;_" -"_;:

o•

::_ • .

I 75

i 650

..

.:

._.-_.,

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.96

.-

and

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:

.

,.• --

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, _-_:_. :.

._._"

,

-.

{'."

•

.92 -

,92

55

l•-.

.o4

•o

.88

I

• ;".._

_...:.'= :,:.:, .: ..

-_'_'_9'-" _

1.16

-"

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,:,. _-." -: _-,,._

1.00

I

¢., -.

1.08

• (,_:

_4

-

i 550

"." o

•_ .=, .'.; "

_ 450

1.20

1.12 1.08

I 350 SOP

•

1.16

I 250

(DEGREES)

1.20 --

t 95

t 105

I 115

1'25

.88 -50

I 50

I 150

offset

I 250

1 350

J 450

SOP

(DEGREES)

corrections

versus

F-4

\

:"

.

-

.-.:..,.

•_ _ •,,_. ,_ ....

-1.5

Figure

•

.--" : -

:._- ,.,-___

"

O_


._; .:, _'_ -'-'_C._J,.I,'_. "%

.:"-

•

•

•

-

• ".._'Jl

'- • f •

.6 .2

=z-J-. '-C,-

_

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r._

_-

-f_;

-,2 .o

._1_

:o.

..oo

.

-.6 %.

(a _ Ii

O_

-1.0

,-'3

:

-1.8

L

-2.2 -2.5

L

-3.0 -3.4

I 75

I 65

55

I 95

I 85

ELONGATION

I

1 281

I

I 105

I 115

u

-1.8 -

E

-2.2 --

E

-2.5 L

Z

-3.0

" .o*_,_

I.

o,

-

-3.4 -50

125

°

I 50

I 150

(DEGREES)

I

I

1.28 -

I

I

1.24 1.20

1.20 -

1.16

1.16 "--

1.08

o

o °,_

,,"

°., "_ _,:.;. "_• el'.--:= t_-

•

1.04 1.00

,

•

1.08 i-

. .... °"

Zl.04

._-_:..-..,.:'__.-.

---

.96

•

.92

;,,,

.o

f

I

°

-_'.-

°-°°

55

I 65

I 75

,,,.

I 85

ELONGATION

F.1

(c)

Gain

and

I 550

650

I

i

I

I

_

,

_.:

'

;'

.

-

_-_°''' •_ _,..1

o

.;.. --

..

o

_'

. .._-:::._. ;.-:_

°,,, :. °

I 95

I 105

.80 .75 115

125

: .--

.88 .84

o

.84 .80 25

r

" .°.

.92., .

_ 450

:,.

_,.

.88

I 350

"-'-

1.12 -

1.12 ,t"

I 250

SOP

1.24

Figure

*

-1.4"

L

-1.4

Z 5

"

LL >,-1.0

-50

_ 50

• "...... ..

i 150

corrections

.:_ ..,

i 250

! 350

versus

F-6

elongation

and

SOP,

. - • _-

I 450

SOP

(DEGREES)

offset

.

60/am

l 550

.

650

APPENDIX Zodiacal

Dust

Cloud

G

Modeling

Using

IRAS

Data

J. Good G.1

Overview A physical

model

for the

interplanetary

dust

cloud

was

model consists an inclination

of spatial distributions for the dust volumetric and line of nodes for the cloud, and a simple

emissivity

a function

as

as r -ls distance

of wavelength.

The

coordinates

and

z is the

distance

from

density drop-off differs from the r -13 power measurements of scattered sunlight, but the dust

decreases

The

IRAS

consequently comparison and

IRAS

emissivity

was

x exp[-4.97(lzl/r) 126] and the temperature as R -°a6, where from the Sun in spherical coordinates, 7" is the radial distance

cylindrical

the

volumetric

fit to the

emissivity and parameterization

Price

data

heliocentric

are

plane

law for the discrepancy

This

found

to vary

R is the radial from the Sun in

of symmetry

of the

dust.

This

dust density deduced from Helios can be explained if the albedo of

distance.

limited

to

solar

elongation

angles

between

60 ° and

120 ° and

are not sensitive to material closer to the Sun than about 0.9 AU. However, of the predicted model flux and Zodiacal Infrared Project (ZIP) data (Murdock 1985)

agreement

with

the

data.

temperature, of the dust

which

in shape

looked

(Figure

to within G.1),

22 ° of the

though

there

Sun

at

10 and

is a calibration

20 #m

scale

shows

excellent

discrepancy.

It also

implies that the r -1'8 power law is good to 0.4 AU. The inclination of the zodiacal dust cloud is 1.7 ° and its line of ascending nodes is at 69 ° ecliptic longitude, substantially different from the 3.4 ° and 87 ° deduced from the Helios measurements. However, since the Helios

measurements

were

to material

outside

sensitive symmetry

plane

The

model

calibration. that

the

with

between

presented

here

and

is based

offsets

on the

of IRAS

require

the

variability

of the

and

the

IRAS

differences

infrared

IRAS data

small

Supplement, 19 July 1993). Consequently, zodiacal dust cloud need reinterpretation. curately

1 AU these

data

is primarily

to variation

of the cloud

distance.

comparisons

gains

0.3 and

0.9 AU, we attribute

heliocentric

Preliminary IRAS

made

data

with

change

the

and

after

COBE-DIItBE

data

(§IV.D.3

the physical However, the

background

as understood and

DIRBE

the

Explanatory

parameters deternfined for purpose here is to represent the

current

model

final

suggests

does

that

the acquite

well. G.2

Data Tile

acal

IttAS

dust

cloud.

data

provide

First,

us with

the sheer

an unprecedented

volume

of data

makes

opportunity it possible

to investigate to fit for a large

of dust cloud parameters unambiguously. Furthermore, the extremely allows differentiation and exclusion of Galactic IR structure. Finally, age

(7

140 pm

in four

bands)

allows

concurrent

information. G-1

extraction

the

zodi-

number

high signal-to-noise the spectral cover-

of temperature

and

emissivity

-8

10

10 .9

"C

0-10

_

-11

10

-

m

m

I

-12

10

0

I

I

I

30

I

I

60

I

I

I

90

I

I

I

I

120

I

I

150

I

I

180

Solar Elongation Figure

G.1

ZIP

data

(Murdock

and

Price

1985)

showing

zodiacal

brightness

ecliptic plane as a function of solar elongation. The dashed curve represents flux (scaled by a factor of 1.5) from the zodiacal dust cloud model.

G-2

the

in the predicted

The

IRAS

orbital

satellite

plane

through

roughly

the year

during

normal

pointed

pole

half

orbit

from

the

Sun

by varying

from

the

Sun

(the

The

solar

elongation

The

azinmth

-90

° when

scan. the

(i.e.,

Since

back

The

sky

tant fluxes

and

by as much

the

part

appendix

satellite out

north

with

ecliptic

of the

orbit

from

but

the

angle)

has

the

side

pole

any

given

rate

or away

come.

+10 °.

defined

to be

of the

Earth

of the opposite

in the

of the

be

s -1).

within

direction

Many

will

angle

(3.84'

in the

of 0 ° looks

plots)

ecliptic

toward

is arbitrarily

the

path

sky at a constant

increases

on

Earth on

either

the

precessed scan

during

was usually

an inclination

(particularly

from

azimuthal

normal

occurred

a line

tilted

with

orbit

nominal

on the

a constant

and

The the

however,

was

pole

G.2),

which

traced

a cone

inclination

(see Figure

direction

and

oriented

G.2). Thus

In practice,

as -I-30 ° from

to as the

in the

given

Earth's

coordinate

in this

solar

system. observed

modeling often

through

(Figure

G.3)

play

be

four

wide

(IRAS

to use the

distance

will

the

angle)

in this

was

for the

other)

elongation

of motion

100 #m

heliocentric

Earth

Sun.

swept

passes

elongation/inclination

the the

It then

descending

references

to the

(referred

satellite

the

25, 60, and

pole

from

from

(Figure

to the Sun.

amounts.

varied

direction

plane

angle

one

solar

away

of 99 ° inclination

vector

orientation

90 ° away

angle

the

Earth's

orbital

from

orbit

Sun-Earth

constant

directly

in a plane

in a near-polar

to the

to maintain

an orbit

to ecliptic

was placed

exact

bandpass

an important

given

bandpass

Explanatory role

in in-band

filters,

shape,

in the

Wm-2sr

nominally

Supplement

-1

since

temperature

observed and

infrared

only

centered

1988, §II.C).

variations flux.

converted

at

12,

It is imporwith

Consequently,

to MJy

sr -1

when

appropriate. Almost to pole.

6000

Of these,

elongations shown

and

were

made

200 scans

were

which

in Figure The

scans

uniformly

major

portion

of the

The

become

at 100 #m.

dominant

noise

is too small

to be a major local

minima

devised

G.3

mission,

which the

about

were

time

1700 of which

representative

period

of the

went

of the

mission.

from

range

pole

of solar

A typical

scan

is

flux seen

in the

that

It is important on these fitting

of "lower

this problem

no zodiacal flux.

at 12, 25, and

variations

to note

plots; since

envelope" on the

that

the typical it implied rather

will be discussed

emission

60 _m is due to the

zodiacal

are left are due to Galactic these SNR that

than

the

the

in the section

sky that

was not

fluctuations

is about

are

1,000).

model

data

should

as a whole.

on fitting.

contaminated

emission

sources,

which

not

This

noise proved

be fit to the The

method

At 100

/zm there

by a large

amount

of Model

Density An

most

chosen covered

local

to show

problem

Description

G.3.a

small

in a kind

to handle

was almost of Galactic

the

G.4.

we wish to model. (the

during

adequate

important

variation

of dust

Poynting-Robertson

representation factor

for

in modeling

density effect)

with

the

of the

heliocentric

would

produce

spatial observed distance a radial G-3

distribution infrared (where distribution

of the flux. the

zodiacal

A simple dust

spirals

proportional

dust model in due to r-1

is the for the to the (Briggs

ECLIPTIC POLE ((_=270) INCREASING

TO SUN

SCAN

\ \

Figure

G.2

The

scanning

geometry

of the

IRAS

nate system is defined by the solar elongation angle the inclination angle ¢, which changes at a constant

G-4

satellite O, which rate.

is illustrated. remains

The fixed

scan

coordi-

for a scan,

and

I

I

I

I

I

I

I

I

I

I

i

1

I

I

m

I

i

O --LO

o m

o_

I-i

O ¢3

_

Ib--

_o ._ V

o q',1

D

o_

I

o_ m

O

O I

uo!ss!msue_±

G

eA!_,eleEl

.5


1. In this study the radial part of the r -_ where a is a free parameter (r is the radial in cylindrical The data,

Leinert

of density

Wikan

1980)

study the z-dependence free parameters. In practice, our

used

not

that

that

density

same

p0, ol, fl, and

G.3.b

Temperature Gray

distance)

when

(with

heated

as R -°'s.

However,

ideal

Consequently,

case.

a free

parameter.

with

variation The

heliocentric

The

diameters

by the

complete

the

can

]

constant

distance

at 1 AU (T0)

of the

to deal

local

6 are

To and

G.3.c

Emissivity The

of the

emission

IRAS

band

free

parameters

behavior passes

However,

it became

clear

necessary

to attenuate

the

of solid

making

from

fitting

(where

emissivity

that

this is a level

the

60 and

of complication

out to some

that

unwarranted

that

6 is

a constant

(2)

infrared

a long

wavelength

6

data

then and

the

is complex

and

the

breadth

composition.

emissivity emissivity

drop-off

was

produced

(Roser and Staude 1978) 10 to 25 #m region but fall

drops the

Sun).

about

(a flat

Consequently,

(A0) and by the

from

statements

predictions

wavelengths.

G

this

properties.

distance

definitive

model

cutoff

varies

as R -_ where

It is assumed

dust

that

will disturb

to vary

Models of dust grain properties are reasonably constant in the

r] = 1 - 3) for longer

is constant

radial

in the any

100 #m

temperature

K

R is the

particles

precludes

too much flux in these bands). indicate that typical materials off as t-,1

(and

heliocentric

is

r = To(Ro/R) where

coordinates.

with

or wavelength

is also free.

temperature

(I)

albedo

temperature

with

complete

is then

(r, z) are cylindrical

with

is sufficient

and

cm-'

of properties

the

3' are

cross-section

however,

cross-section

rise to an equilibrium

we allow

In this

= 1AU, z = 0).

absorption

and

models and

absorption

be used,

R0 = 1 AU, and

fit Helios

] where/_

volumetric

form

To

appropriate.

exp[-3(tzl/r)_

× exp[-#(lzl/r)

study

clear.

Collision

be more

po = p(Ro

>2>wavelength

temperature

description

is less

Sun will give

in this

distance

but

value

7 are free parameters,

particles

form

volumetric

p(r,z) = po(Ro/r) where

2] might

functional

of the

ecliptic

of exp[-2.1(Izl/r)].

exp[-/_r

a reference

description

of the

to be of the

the

the

of p(r, z) with

plane

a z-dependence

is assumed

We will assume

complete

of the

indicate

we model

description The

out

et al., (1978a)

and

p(r, z).

is assumed to vary as distance from the Sun

coordinates).

variation

(Trulsen

density distribution component of the

et al. 1981) vary as r -k

this study as A-_.

has used

In practice,

two parameters,

an

even

A0 and

r/,

cannot be fit simultaneously (they are to() strongly correlated). _Vetherefore arbitrarily choseto let r! = 1 (Mie theory for spherical particles). This approximation will be shown to have no effect on any of the parametersother than A0. The complete description of our model for the emissivity is

eo e0(_/A0)-'

e= where

Ao is a parameter.

volumetric G.3.d

absorption

Cloud The

have the

zodiacal

dust

cloud

in different the

is assumed

relative

angle

to tile

i and

will be in error

to detect

and

will be subsumed

by no,

the

is allowed

to

cross-section.

an inclination

symmetry

e0 is an unknown

(3)

Orientation

inclination

nodes

In practice,

< Ao __ > A0

parts

presence

the if the

of the

ecliptic.

This

line

of ascending

cloud

is warped

solar

of such

to be azimuthally

system

introduces nodes

and

in the

two

ft.

thus

(Misconi

discrepancies

symmetric The

has

but

more

different

1980).

free

of azinmthal

inclinationslines

We should,

residuals

parameters:

assumption

of

however,

be able

to the fit as a flmction

of solar

elongation. G.3.e

Constant

Background

It became only

apparent

is unclear;

it could

component COBE

each

that

the

on the

sky.

A detailed

comparison

with

may

resolve

this

for the

a total

of fourteen

temperature,

However,

the

free

parameters

parameters

emissivity,

as inentioned

and

previously,

simultaneously

to 13. Although

Fitting

ZIP

origin

emission of this

an isotropic

(Murdock

could

extra

flux

background

and

Price

1985)

or

this

scan.

z-dependence temperature

simple

Such

of the and

to generate

a fit gives density

is insensitive

To determine fllll time

the

cloud

model

therefore,

of parameters

the

may

for the and

to derive total

seem

(samples)x4 to make

(four

orientation,

it is impossible

and,

number

in our

four

values

number

density, for the for both

of parameters

excessive,

the

number

of

(bands)]. It will be shown a unique solution possible.

Procedure

It is relatively

the

represent

the

zodiacal

The

Parameter_

emissivity

of one

of the

band.

uncertainty.

degrees of freedom is large [_ 200 (scans)x360 that these parameters are sufficiently uncorrelated G.4

shape

in each or it might

are thus

is reduced

fitting introduced offset,

background). of the

the were

a calibration

Model There

offset

be

data

G.3.f

two

during

be fit if a baseline

range

the

cloud

of tile

a model

a moderately but

does

to the orientation mission

that

good

is capable

estimate

not

do well on

cloud

inclination

parameters

(equivalently, G

radial

and requires

the 7

the

of fitting

of the

range

one

paraIneters

wavelength defining

dependence

the

of density

or

line of nodes. several of Earth

scans

spread

orbital

out

over

longitudes).

In addition,

to

requires

use of the

the

determine

temperature

and

Preliminary

fitting

1986)

gave

than

the

values

those

with

dependence

elongation

emissivity of our

for

and

radial

of solar

the

a subset

effort

the

addition

to its by some

a smooth

Galactic

celestial

zodiacal

Finally,

we must

and

data

of the

parameters

fit but

fit (further

dust

We

are

cloud),

used

amount

and

(Good,

with

temperature

to constrain

fit all four much

the

at once.

and

higher the

fully

bands

Hauser

emphasizing

fitting can

to both

simultaneous

Gautier

uncertainties

need

flux

integral

along

any

conclusion

that

to the

for the

¢ are

as described function,

above R_o(1)

wavelengths at time

the

elongation

full

[with is the

._o = (12,

t.

Positions

25,

60 or 100 #m)

in (rc, Zc)-space

orbital position of the Earth at time orientation of the dust cloud.

are

be sensitive

of the

the

to

cloud

above.

The

using

method

a

of least

]

not

e is the

calculated

p(r, z) and

ecliptic)].

B)_(T)

vector

eccentricity

with

in the

(e, 0, ¢) taking of the

T(R)

is the

combination

unit

from

(4)

dl

observation,

detector/filter

t (including

on

of the

by

of the

and

is out

position

amounts

200 scans

using

p(r_,z_)B_(T(R))de

of the

same

described

of all

parameters

coordinates,

response

of scans

[/0

inclination

(re, zc in cloud spectral

the

derivation

estimates

scan

to separate

different

accurate

full subset

is given

R,ko(,,_)

and

an

the

a single

will implicitly

model

line-of-sight

J_min

0 and

covering

through

simultaneously

to generate

[Am'_

FAo(O,_),t)-_

(i.e.,

cloud.

parameters, It is impossible

if two scans

given set of model parameters, and b) to adjust squares until the best fit is achieved. The

model light.

to the

fitting is a)

the

times

scans

be due

to the

fitting

but

at different

only

forced

in the

all

of Galactic

in one scan,

observed

which

requires

procedure

to constrain

are

therefore

parameters

inability unknown

component

sphere

variability,

where

angles.

properties

model

a poorer

of density

set).

In

time

with

credible

contaminated the

full range

to estimate

present

parameter

accurately

Planck nominal

direction into

Earth's

are

(0, ¢)

account

orbit)

the

and

the

To generate the model scans, the flux several lines of sight and over the bandpass.

from the Thirteen

model cloud was integrated along reference points were used for each

scan,

-90 ° and

+90 ° but

spread

ecliptic

out

plane

between

where

points

was

interpolated,

of the

real

data

integration Each slightly. ferences

the

points.

is typically parameter The between

updates to the eters converged.

inclination variation using The

variations the estimated

was a cubic

most

of the model

The

under

between

resultant

tension,

this

concentrated

toward

flux for the

to give model

interpolated

reference

fluxes

function

and

the

for each a full flux

0.05%.

model

nominal

extreme.

spline

difference

less than in the

angles

(the

model model

thirteen with

and

the

parameters.

respect real This

G-8

described to these data

were

procedure

above)

was

then

perturbations then was

and

combined

iterated

perturbed

until

the

dif-

to generate the

param-

As mentioned but

Galactic

the

model

weight

previously,

structure. (when

to

exclude

incorporated

into

the

scheme.

the

longer

G.4.a

The cients

the the

results

galaxy

become and

points

the

zodiacal

envelope" Galactic

zodiacal

background

are strong

positive

accurate) (lust

since

should

bands.

approach

be given

Such

an uncertainty

our model

between

the

to the 200 scans

parameters

are

are shown

shown

point

be biased,

in Table

in Table

elongations and times) are shown in Figures G.4, of parameters, even the highest of the correlations on

p and

T) is quite

in our

from low

can

be

is part

of

especially

at

model

small.

We therefore

is justified

and,

G.2.

the

coeffi-

Representative

scans

G.5 and G.6. Considering (0.91, between the power

conclude

moreover,

G.1 and

that

that

the

inclusion

they

are

all

of all

required

properly.

Model of Parameter

Density

Parameter Values

Temperature

Emissivity

G.1

Values

and

Uncertainties

of Parameters

Po = 1.439 -1- 0.004 c_ = 1.803 + 0.014

Units cnl-

x 10 -2°

unitless unitless

7 = 1.265 -t- 0.003

unitless Kelvin

To = 266.20 + 0.18 6 = 0.359 + 0.004 _o = 37.75

unitless

+ 0.09

[/, In

(fixed)

r/=l Orientation

1

+ 0.024

/3 = 4.973

0 = 68.61

+ 0.03

degrees

i = 1.73 4- 0.01 Offsets

noise

a very

a weighting

for each

the fit would

are not excursions

emission.

Table

Class

the that

reasonably

process

"lower

by the

of fitting

parameters data

has

above

those

Results

law exponents fit the

fluctuations

least-squares this

of correlation

free

model

Without

(for several the number the

the

wavelengths,

Model

the

Consequently,

degrees

12 #m = 35.53

4- 0.15

x 10 -s

Win-

25 #m

= 49.97

4- 0.14

x 10 -s

Win

60 #m

= 2.19 4- 0.03

100 #m = 5.24 4- 0.07

G

9

x 10 -s x 10 -s

2 sr-

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sr-

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Inclina'don (degrees)

Figure (solid

G.4 line).

as bumps is Galactic

A typical This

scan

at the ecliptic emission.

IRAS

Inclinal_on(degrees)

pole-to-pole

was at a solar plane

scan

elongation

(inclination

with

the

zodiacal

of 90 °. The

zodiacal

180 °) and

G

10

at 4- _ 10 °. The

dust dust

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model

fit

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105

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material

i 180%

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Inclination (degrees)

InclinaSon(degrees)

Figure G.5 of 112 °. The

1 ,_ 0

dust cloud model and less intense

farther

from

the

Sun,

G

11

height.

prediction than those which

for a scan in Figure

is both

cooler

at solar elongation G.4 since this scan and

has

a larger

z

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Figure of 67 °. narrower

G.6 The and

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I

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Inclination(degrees)

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cloud

model

in Figure scan

G.5

prediction exists

is observing

G

12

for a scan for

these

material

data. closer

at solar These to the

elongation profiles Sun.

are

Table Correlation

Coefficients

G.2

Between

Model

Parameters

Parameters Offsets 25 -.11

(pro)

60 0.00

100 0.00

p0 0.30

0.06

0.01

-0.52

0.03

-0.06 -0.02

a 0.24

/4 0.24

7 0.18

-0.28

0.27

0.19

0.56

0.32

-0.08

0.04

0.03

0.08

0.09

-0.31

-0.04

-0.02

0.01

0.01

0.02

0.02

-0.05

-0.01

0.25

0.0

-0.86

-0.55

0.31

0.20

-0.77

-0.91

0.12

0.89

-0.08

-0.08

0.1

-0.47

-0.19

-0.06

-0.11

0.12

-0.56

-0.10

0.18

-0.09

0.73

To -0.44

6 -0.26

A0 0.00

_ -0.05

0.34

-0.11

-0.17

0.78

-0.09

i -0.01

12#m

0.04

25tim

-0.01

60pro

0.00

0.14

-0.19

0.06

-0.16

100#m P0

7

To

0.11

-0.05

-0.09

-0.0

-0.05

Ao

-0.09

Ttle

complete

volumetric p = 1.43

and

the

temperature

emissivity

x 10-2°(Ro/r)l8°

implications

here,

but

terms

of these

some

are

background The various

materials

(eg., about

olivine,

approximation long the

wavelength IRAS

filters

126]

by

(5)

CFI1-1

properties (Roser

30 pm

and have

but

the cloud

emissivity

material Models

1978)

crude, relatively finer

flat

drop but flat

are extremely

results

emissivity

that

several

very

uneven)

analysis

of the

of our between

is needed.

Both

of these

approximation

uncertain,

likely

and

10 and

although

tile

a decreasing

of the dust.

for the

properties

to beyond

30/tin.

their

behavior

candidates

emission

3) out

fit require

composition

G - 13

will not be discussed

absorption/emission

off as A-'_ (n = 1 -

the

(6)

effect.

of the

show

(though

terms

it is a crude

a calibration

of the dust high.

parameters

background

because

quite fairly

and

orientation

and

emissivity

Staude

then

is very

precludes

K.

well be merely

is probably

obsidian)

10 and

exp[-4.97z/r

is given

°'36 and

the

it may

emissivity

emissivity

of the

ambiguous,

because

overall

profiles

discussion

quite

description

by T = 266(Ro/R)

The

distribution

The

dust

between

100 pro. emissivity large

for

width

Our at of

References Briggs, R.E. 1962, Astron. DIRBE Center

Explanatory (NSSDC).

Good,

J.C.,

IRAS

Hauser,

H.J.

and

T.N.

in Space

Atlases:

Habing,

P.E.

and

Leinert,

C., M. Hanner,

H. Link

Leinert,

C., M. Hanner,

I. Richter,

Leinert,

C.,

Misconi,

N.Y.

Particles

in the

Mukai, Murdock, Roser, Trulsen,

T.,

and

1980, Solar R.H.

T.L.

and

S., and

H.J.

J., and

"The

Giese S.D. Staude

A. Wikan

and

B. Planck

eds. 1984,

Price

1980,

I. Halliday Astron.

1985,

1978,

Plane

Astron. Astron.

1988,

of the and

Aatron. Astron. Zodiacal

B.A.

Y., 90, 375.

A_trophys., Astrophys.,

G - 14

C.A.

87,

381.

91,

155.

of the

Data

Zodiacal COSPAR

Beichman,

G. Neuge-

D.C.:GPO). 63,

183.

Astrophya., A_trophya., Astrophys., Cloud

Mclntosh,

131,355.

Science

of the XXVIth

ed.

Astron.

1981,

Space

Observations

A_trophys.,

1980,

Astrophys.,

Aatron.

IRAS

(Washington,

1978b,

E. Pitz

by National

Proceedings

Astron.

E. Pitz

Symmetry

System,

1986,"

Chester

1978a,

and

and

1986,

Supplement T.J.

E. Pitz

E. Pitz,

distributed

Research

and

C., M. Hanner,

1993,

Gautier

Explanatory Clegg,

Leinert,

I. Richter,

710. 19 July

and

in "Advances

Catalogs

bauer,

Supplement

M.G.

Background, Meeting.

J., 67,

Near

84,

119.

82,

328.

103,

177.

1 AU",

(Reidel:Dordrecht),

in Solid 49.

APPENDIX Zodiacal

H.1

The

IRAS

ZodiacM

problem

2.0,

which

that

are

outlined

found

in Version

All references 3.1. The proved

to Version

major and

rerun

change,

History

Version

improvements

and

History Version

File 3.0

(ZOHF)

Introduction

It replaced

was

H

below.

3.0.

with

the

were

improved

processing

to be an exhaustive

essential

information

of the

in the

calibration.

effects

Other

improvements, Results

and

The

changes

of the

to enable

baseline

Version

ZOHF

tests

a researcher

to use

below.

was

IRAS

included

presented.

3.0 or its the

a

to Version

a format change, This

analysis.

ZOHF

im-

survey

a sampling

are

Version

of

fixed

is given

entire

improvements,

ZOHF

3.1,

calibration

The

to the

in 1988.

a number

are applicable

incorporated.

position

by IPAC

its effect

in §H.8

of tile verification

description

is presented

than

were

in 1990,

problem

other

released

3.0 incorporates

release

appendix

calibration.

changes.

intended

3.0 was Version

A subsequent

for hysteresis

calibration

Version in 1986.

A statement

improvements

additional

(ZOtIF)

released

3.0 in this

corrections

several

File was

Version

is not Only 3.0

product. The

ZOHF

are, however,

Product The

data

seconds pixel 2.0. focal

Version

all detectors,

of time. sizes

Due

remains problem

the

differences

a systematic is discussed

final

at the

calibration

few-percent

of the level

IRAS

between

difference between ascending and in the section on anomalies below.

data.

observations. descending

There In scans.

Description

ZOHF

from

3.0 incorporated

still calibration

particular, there This systematic H.2

Version

This

are given to elimination

3.0 was created except

the

resulted

in Table

in the same

1/4

sized

manner

detectors,

in an approximately H.1.

of the

The

smallest

beam

sizes

detectors,

as the previous were

square

Table Pixel

Wavelength (_m)

Sizes

have

not

are not

Pixel

H.1 for

ZOHF

Size (arcminutes)

In-Scan

Cross-Scan

12

30.8

28.4

25

30.8

30.3

60

30.8

28.5

100

30.8

30.5

H

1

beam

they

plane.

boxcar

changed the

versions.

averaged 0.5 ° wide. from

those

full width

IRAS

over

eight

The

exact

in Version of the

IRAS

H.3

Format The

record

2.0 to give H.2.

format

UTCS

of the

ZOHF

in centiseconds

Version

instead

3.0 has

of seconds.

Table Format (Replaces

name

description

format

format

of Version

is given

Version

Explanatory

Supplement

1988)

units

type

NSOP

SOP

Number

I3

NOBS

OBS

Number

I3

7

NUTCS

Time

UTCS

1

in Table

3.0

1

centisec

I10

Inclination

degrees

F6.2

Solar

degrees

F6.2

degrees

F6.2

17

INCL 1

23

ELONG

29

BETA

Ecliptic

35

LAMBDA

Ecliptic

degrees

F6.2

41

I_

12 #m

Brightness

Density

Jy/sr

E10.4

51

I_,_

25 tim

Brightness

Density

Jy/sr

E10.4

61

1,3

60 #m

Brightness

Density

Jy/sr

El0.4

71

I_,4

100 #m

Jy/sr

E10.4

to page

X-62

1

of tile

IRAS

Elongation Latitude Longitude

Brightness

Explanatory

Density

Supplement

1988

for definitions.

Processing Several

in Version different Version

improvements 2.0 was

in data

corrected.

calibrated

using

Version

In total,

Version

3.0.

processing

The

from that of Version 2.0 was included for

be properly

prior

new

the

4

Refer H.4

in IRAS

byte

The

from

H.2

of ZOHF

old version

changed

set

were made

of observations

average

position

3.0 and

in Version

an error

3.0 is slightly excluded from that could not

the

excluded

new

stimulator

3.0 contains

extraction

0.07%

fewer

glitches

method

were

observations

were

removed

than by

Version

a deglitch

from 2.0.

processor

data used in tile ZOHF Version 2.0 were destriped with an algorithm the gain and offset of each individual detector in a band to match those of all detectors

should have and did not An

contained

Version

2.0. A small set of survey scans erroneously the first time in Version 3.0. Observations

Radiation spikes and other electronic to resampling the data (§III.A.3).

The adjusted

for ZOHF

in that

band.

This

destriper

little effect since the destriper left the affect the striping caused by calibration

error in-scan

was

found

in Version

by 115" for half

2.0

and

of the mission H-2

was

used

for Version

average value of the variations between

corrected data.

not

in Version

Improvements

ZOHF scans.

3.0 that in the

which of the

3.0.

unchanged

advanced

satellite

This

the

pointing

reconstruction made to support the IRAS the

ZOHF

to the

Version

resolution

The

impact

ZOHF

interval

adjacent

adjacent in-scan to Version 2.0.

The

of the

sampling

between

H.5

3.0.

ZOHF

pixels.

pixels,

of these

Source

Survey

improvements

1992

were

is generally

incorporated

not

large

in

relative

(§III.A.3).

in the

in-scan

Paint

Version

Because

the

3.0 is eight

ZOHF

the file size of Version

seconds

Version

and

there

2.0 was made

3.0 is reduced

by a factor

with

is no overlap overlapping

of two as compared

Calibration Several

detailed H.6

important

in §III.A.2

Analysis Several

characterize H.6.a

Gain

minima

analyses

it with

respect

and

the

approximately for Version a linear sources

in the

IRAS

calibration

software.

the

Version

These

are

done

at IPAC

to Version

intensities, The

covered

given

expected

mission

offsets

of these

in Table

H.3.

from

calibration

extremes

to the during

and

3.0 observation

the of gain

ZOHF

3.0 data

and

detector

Gain

and

Offset

Compared Wavelength Coefficient

Band

GAIN

OFFSET -1)

The

and

was linearly

fit to its counterpart

fits

as

changes

offset

nonlinearities

as well

mission are

mean that

caused

encountered

the

maxima

and

gain

and

were

implemented

by

attempting

when

especially

offset

bright

(#m)

H.3

of each

Version

to each

Version

Mission

Error

Mean

Mean

3.0 2.0

Observation Observation

of (1 c,)

Mission

Mission

Maximum

Minimum

12

0.896

0.013

1.083

0.685

25

0.919

0.022

1.420

0.713

60

1.075

0.042

1.344

0.706

100

1.031

0.082

1.999

0.505

12

-0.028

0.072

.441

-0.680

25 60

-0.158 -0.008

0.065 0.021

0.452 0.120

-1.092 -0.142

100

0.014

0.018

0.227

-0.118

g

--

3

is

to fit

a scan.

Table

(106 Wm-2sr

to verify

2.0.

Version

gain

are

value

The

each

average

mission the

3.0.

were

Offset

transformation are

made

Supplement.

general

2.0. for

of this

were

Results

To compare in Version

changes

H.6.b

Position The

cumulative

effect

of the

position

correction

and the

improved

can be shown by differencing the position given in the ZOHF Observation Parameter File for each ZOHF record in Versions Parameter

File

is an internal

scan

to an accuracy

Note

that

Version Version would

Version 2.0.

3.0 positions

are

20".

Histograms

3.0 compares

It should the

file that

of about

much

also be noted

2.0 Observation reflect

IPAC

actually

to the

both

does

better

not

than Table

differences of the

It is likely

histogram

the

of Comparison Observation

Difference

(")

Version

of ZOHF Parameter

Positions File

Version

3.0 (%)

2 (%)

39.0

37.7

10-20

15.7

23.6

20-30

9.1

17.4

30-40

5.9

12.0

40-50

4.2

7.0

50-60 60-70

3.3 2.7

2.1 .1

70-80

2.5

**

80-90

2.2

0.

90-100

1.9

0.

100-200

11.9

0.

200-300

1.5

0.

300-400 400-500

** **

0. 0.

500-600

0.

0.

600-700

**

0.

700-800

**

O.

800-900

O.

O.

900-1000

**

O.

1000-2000

**

0.

**

0.

** represents

a percentage

H-4

< .05

the

for each

in Table File than

compared

Parameter that

shows.

0-10

>2000

were

H.4

Histograms with

given

Parameter ZOHF

scheme

predicted in the The Observation

information are

3.0 Observation

exist). the

the pointing

Observation

versions

File (a Version

pointing, slightly

of these

better that

Parameter

improved

summarizes

interpolation

to a position 2.0 and 3.0.

File, ZOHF

H.4. does to the which

Version

H.6.c

Calibration M.G.

Verification

Hauser,

L.J.

formed extensive Their results are If the the

calibration

during

daily

TFPR

t)rightness between

H.1.

scatter

were

some

the

survey

is seen

should

measure

of the

agree

with

stability

Flight

and

the

TFPR

the

these

3% at 12 and

TFPR

used

during

two

of the

model

25 ttm,

per-

of the

model

uncertainty and

have

consistency.

brightness

between

and

TFPR

Center

calibration

tile

discrepancy

of the

to be approximately

level

perfectly,

The

observations

Space

noise

working

observations.

gives

at Goddard

checking

observations

calibration

difference I00

J. Vrtilek

system

survey

baseline

The

and

analyses of the ZOHF summarized here.

IRAS

measured

Rickard

values

baseline.

is shown

of The

in Figure

4% at 60, and

8%

at

#m. We should

model

that

TFPR

be able

we used

model

that

part

This

check

variability

due

seriously.

descending H.7

model

accurate

Hauser

the

same

variable

part

et al.'s

check

of the

variable

of the symmetry the

the

and

free

the

and

et aI. also

scans,

see §H.7

of the

ZOHF

zodiacal

that

data

alone

enough

systematic

the

differences

part

both

drift.

of the

reproduced above.

ecliptic

poles.

Derivation

is unreliable

to affect

TFPR

discussed

cross

of baseline

of the

dust

consistency

scans

effects

survey

of the

internal

of survey the

are large found

plane

model's

ends from

from

not eliminated

survey

ZOHF

Hauser

to within

to eccentricity are

the

calibration.

by differencing

quite

drifts

from

inclination

TFPR

is done be

baseline

in the

to the

of the

It should

term

due

to re-derive

of the

because

calculated between

residual

eccentricity ascending

and

below.

Anomalies Several

which

users

progress

with

plane

than

are

the

Note

that,

in the

Version

decreasing ascending

IRAS

2.0 have

ecliptic scans

orbit,

found

latitude)

(scans

descending

are

that

the

descending

systematically

which

progress

scans

always

with

brighter

increasing

look behind

scans

(scans

at the

ecliptic

ecliptic

the

latitude.)

Earth

in its orbit

while ascending scans always look ahead. We have investigated this effect and found that a discrepancy on the order of 2% (2% at 12 and 60 ttm, 1.5% at 25 tim, and 4% at 100/_m) is seen the

at the

north

ecliptic

sets

of scans

are

two

zero.

The

error

This the

detector

after

DC

the

at the

same

could

pole

crossing was

a scale

few-percent

level.

the

to the

survey

scans

following

an

group

of scans,

which

to the

scan

SAA are

further

part

the

after

to vary

the

This

descending These

scans

have

SAA

and

H

5

are

AC

in the

only may

dominate

the fluxes

predominantly

At the

DC

and

first

be

response

of

implemented

for the not

pole

should

calibration.

model

response

assumption

elevated

scans. difference

DC gain

The

derived

the

scans

the

effect

(SAA).

was

with

and

of the

hysteresis

SAA

linearly

descending

sky

Anomaly

AC response.

from

and

of the

uncertainties

Atlantic

strategy,

crossing.

ascending

by a residual

South

hysteresis

assumed

factor

is within

be caused

for handling

response

by applying

Due

between

at the

difference

in calibration The

seen

pole looking

AC response. was

obtained

be correct

group

relative ascending.

at the

of survey

to the

next

In Figure

H.1, the abscissais the ratio of the measuredflux at the North Ecliptic Pole (NEP) and the flux calculatedfrom the calibration model and assignedto the NEP. This is plotted against the time from tile SAA crossingfor the 12, 25, 60, and 100 tim bands. If the calibration were the

perfect, time

for each

all measurements

axis.

Figure

grouping

In short,

H.2

attributed

to uncorrected

possibility

that

H.8

Zodiacal

some

3.1.

This

No samples

that

the

mean

a large

calibration of the File

flux

observations

ratio

and

fall

population

into

groups

standard

ascending-descending

At this

is a real

along

deviation

time,

feature

asymmetry

we cannot of the

however

can

eliminate

be the

sky.

3.1

for the

ZOHF

a small

Version

number

at 12 or 25 #m,

at 100 #m. Most of the samples affected at 100/_m were lowered

Tile

100 #m.

of the

drifts.

Version

affected

were affected

part

asymmetry

the averages problem

be unity.

at 12, 25, 60, and

History

In calculating included.

shows

of scans

we believe

would

3.0, some

of ZOHF

one sample

intensities

samples

and

at 60 #m and

were erroneously was fixed

in Version

382 (0.03%)

affected were in short low gain observations. 23%, on average, with a maximum decrease

samples

The samples of 45%.

References IRAS bauer, Moshir, 2, JPL

Catalogs

and

Atlases:

H. J. Habing,

Explanatory

P. E. Clegg,

M. et al., 1992, Explanatory D-10015

8/92

and

Supplement T. J. Chester

Supplement

(Pasadena:JPL).

tt-6

1988, ed.

C. A. Beichman,

(Washington,

to the

IRAS

Faint

G. Neuge-

D.C.:GPO). Source

Survey

Version

1.10 12 t.tm X 1.06 £:3 III

_

_

0 UJ n" 13..

_0,,

&' o_o

.

O

0

0 A

1.02

nO

A A

0

A

-......

x

A

A

_ 0.98

o

--

A A

t_

A

0A g

%

_

A

A

A A

LLI > rc

w 0.94 O0

0 0.90 0

I 1500

I 3000

I 4500

I 6000

I 7500 SECONDS

I 9000

I 10500

I 12000

1 13500

[ 15000

1.10 25 I.tm X

1.06 ILl I-0 W n-

1.02

R A

O 0 O O0 0

x

0.98

R ---

l.lJ > rr W ¢/1 rn

R

A

0

0

R

A O

A A

g

A

A

A

A

0.94

O 0.90

0

I 1500

I 3000

l

I

4500

6000

I 7500 SECONDS

I

I

I

I

9000

10500

12000

13500

Figure H.1 Flux ratio at North Ecliptic Pole vs. time 12, 25, 60, and 100 #m. (See text, Anomalies.)

H-7

(seconds)

1 15000

from SAA crossing

at

1.10

60 pm X -J

LL 1.06 a LM t-O a 1.02 LU rr 12. X 3

w

--

w

0.98-

w

)11

II

}i

Q uJ :> rr w 0.94 m 0

t

-

I

0.90 0

I

1500

3000

I

I

I

I

I

I

I

I

45O0

6000

7500

9000

10500

12000

13500

15000

SECONDS 1.10

1O0 p.m x -J

LL 1.06 D LU _t-O n 1.02LM

rr 13.. X :::3 " 0.98 LL a uJ > rr W rj) 0.94 133 O

w

I

0.90 0

1500

I 3000

I 4500

I

I

6000

I

7500

9000

SECONDS

Figure

H.2

H-

(cont'd)

10

I 10500

I 12000

I 13500

I 15000

TECHNICAL

1.

Report No.

4.

Title IRAS

Sky

Author(s)

9.

Per_rming

Survey

Accession

- Explanatory

Name

PROPULSION

Pasadena,

91109

Agency

California Name

AERONAUTICS

Washington, Supplementary

D.C.

No.

5.

Report May

6.

Performing

OrganizaHon

Code

8.

Performing

Organization

Report

Date 1994

Unit

No.

No.

LABORATORY of Technology

Spomoring

Reclplent's

10. Work

ondAddress

Catalog

TITLE PAGE

3.

No.

Supplement

California Institute 4800 Oak Grove Drive

NATIONAL

116.

Atlas

Organization JET

15.

Government

and Subtitle

7.

12.

2.

"94-11

REPORT STANDARD

Ill. 13.

Type of Report

Supplement Atlas

and Addre_ AND

Contract or Grant NAS7-918

SPACE

ADMINISTRATION

!14.

to

Sponsoring

No.

and Period Sky

Agency

Covered

Survey

Code

20546

Notes

Abstract

This Explanatory Supplement accomparfies the IRAS Sky Survey Atlas (ISSA) and the ISSA Reject Set. The first ISSA release in 1991 covers completely the high ecliptic latitude sky, I#l > 50°, with some coverage down to I_I _ 40°. The second ISSA release in 1992 covers ecliptic latitudes of 50 ° > I#1 > 20 °, with some coverage down to J#J 13". The remaining fields covering latitudes within 20 ° of the ecliptic plane are of reduced quality compared to the rest of the ISSA fields and therefore are released as a separate IPAC product, the ISSA Reject Set. The reduced quality.is due to contamination by zodiacal emission residuals. Special care should be taken when using the ISSA Reject images (§IV.F). In addition to information on the ISSA images, some information is provided in this Explanatory Supplement on the/P.AS Zod/aca/H/story File (ZOHF), Version 3.0, which was described in the December 1988 release memo (AppendixH). The data described in this Supplement are available at the National Space Science Data Center (NSSDC) at the Goddard Space Flight Center. The interested reader is referred to the NSSDC for access to the IRAS Sky Survey Atlas (ISSA).

1"7. Key Words Astronomy Astrophysics Astronomical Infrared Infrared Infrared 19.

(Selected

Images

Sky Survey Atlas

Security

Cl_slf.

Unclassified

_f

byAuthor(s)) i Infrared Images Atlas

18.

Distribution

Statement

Images

Sky Surveys IRAS i IRAS Images this repo_) 20. Security

Clmsif.

Unclassified

_fthis

page)

21.

No.

of

Pages

22.

Price

164 JPL

0184

R9183