Geocenter Geocenter coordinates coordinates ...

Geocenter coordinates from SLR and combined GNSSGNSS-SLR analysis D. Thaller (1), K. Sośnica So nica (1), A. Jä Jäggi (1), R. Dach (1), G. Beutler (1), M. Mareyen (2)

(1) Astronomical Institute, University of Bern, Switzerland (2) Bundesamt für Kartographie und Geodäsie, Frankfurt a.M., Germany

EGU General Assembly 2012, Vienna

Astronomical Institute University of Bern

D. Thaller et al.: Geocenter coordinates from SLR and combined GNSS-SLR analysis EGU General Assembly 2012, Vienna

Overview

Geocenter from singlesingle-technique solutions: solutions: Comparison of GNSS and SLR

Geocenter from combined GNSSGNSS-SLR solutions: solutions: Impact of weighting Impact of range biases Impact of microwave antenna offsets (SAO) and laser array offsets (LRA) Impact of orbit parameterization

Conclusions


Weekly GNSS: CODE reprocessing using IGS08 (TRF, antenna model) Weekly SLR: Computed at AIUB, based on LAGEOS satellites 20

10 GCC−Y [mm]


SLRSLR-only and GNSSGNSS-only geocenter series

0

−10 GNSS: Mean = 5.2 mm, RMS = 4.4 mm SLR: Mean = 1.2 mm, RMS = 3.6 mm −20 2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Comparable series from GNSS and SLR (except (except for shift: shift: 4 mm) Astronomical Institute University of Bern

40

GCC−Z [mm]

20

0

−20 GNSS: Mean = 5.9 mm, RMS = 10.7 mm SLR: Mean = 0.2 mm, RMS = 6.4 mm −40 2000 ∆ GCC−Z [mm]



40 20 0 −20 −40 2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

∆ Z: Mean = −5.7 mm, RMS = 12.6 mm

2001

2002

2003

2004

2005

2006

2007

2008

2009

SLR shows clearly fewer variations than GNSS Astronomical Institute University of Bern

2010

2011

GNSS−only (blue) vs. SLR−only (orange) 6 50.0 117.8

5

GCC−Z amplitude [mm]



70.2

364.0

4

333.7

3 166.8

2

GNSS-only 7-day solutions SLR-only 7-day solutions

222.4

182.0 1 0 0

50

100

150 200 250 Period in Days

300

350

400

Draconitic year is clearly visible: GNSS = 352 d, d, LAGLAG-2 = 222 d

Annual and draconitic signal are not distinguishable for GNSS

Big amplitudes at harmonics of draconitic year for GNSS Astronomical Institute University of Bern


Combined GNSSGNSS-SLR solutions

Microwave observations to GPS / GLONASS

SLR observations to GPS / GLONASS

SLR observations to LAGEOS

Connection of SLR and GNSS at the GPS / GLONASS satellites ( „satellite coco-location“ location“ )

No local ties applied


GNSS F7 (blue) vs. GNSS+SLR A73 (pink) 7 50.0

GNSS-only 7-day Combined GNSS-SLR 7-day

6 GCC−Z amplitude [mm]


Combined geocenter

117.8

5 70.2 4

333.7 69.0

3

364.0

114.4

2 1 0 0

50

100

150

200 Period in Days

250

300

Annual signal remains; draconitic GNSS signal vanishes

Harmonics of draconitic GNSS year are reduced but not eliminated

350


400


Combined geocenter: geocenter: Impact of weighting σ SLR_LAG

σ SLR@GNSS

Mean

σ GNSS

σ GNSS

X

Y

Z

X

Y

Z

A

1

1

3.7

4.9

5.0

3.9

5.0

7.6

B

10

10

3.7

4.9

3.8

3.9

4.9

7.9

C

0.1

0.1

4.1

4.8

6.8

4.9

5.8

11.7

D

1

10

4.2

5.0

3.8

4.3

5.4

8.2

GNSSGNSS-only series

4.6

5.2

5.9

3.5

4.4

10.7

SLRSLR-only series

1.0

1.2

0.2

4.1

3.6

6.4

RMS

Higher weight for SLR data (solution C) degrades the solution All other combinations show improvement w.r.t. GNSS-only Down-weighting SLR@GNSS data (B B or D) not necessarily needed Astronomical Institute University of Bern

Considering / Ignoring range biases (per Sta, per Sat): Impact on geocenter 20

∆ X: Mean = 0.1 mm ∆ Y: Mean = −0.3 mm ∆ Z: Mean = 2.5 mm

15

∆ GCC [mm]


Combined geocenter: geocenter: Impact of RGB

10 5 0 −5 2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Comb 1: No range bias considered Comb 2: Range bias per station, per satellite considered ⇒ Bias and annual signal (mainly in z-component): several mm Astronomical Institute University of Bern

2011

Considering / Ignoring corrections to SAO, LRA (RGB applied): Impact on geocenter 1 0

∆ GCC [mm]


Combined geocenter: geocenter: Impact of SAO, LRA

−1 −2 −3 ∆ X: Mean = −0.7 mm ∆ Y: Mean = −0.1 mm ∆ Z: Mean = −1.8 mm

−4 −5 2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

Comb 1: Range bias per station, per satellite considered Comb 2: RGB, SAO, LRA corrections considered ⇒ Bias at mm-level (mainly in z-component) Astronomical Institute University of Bern

2010

2011

GNSS satellites only: only: Test

solution: solution: OPR parameters D, Y, X un-constrained

«Standard» Standard»

solution due to correlations with geocenter: Onceper-Rev (OPR) parameters D, Y fixed GNSS satellites only (MW+SLR): OPR free (cyan) vs. OPR fixed (brown) 16 364.0

50.0 14 12 Amplitude GCC−Z [mm]


Impact of orbit constraints

69.0

10 8

70.2 6

87.0

38.9 58.0

4

117.8

182.0 333.7

2 0 0

50

100

150

200 Period in Days

250

300

350


400

Combined GNSSGNSS-SLR solution: solution: OPR parameters unun-constrained GNSS satellites only Combined GNSS+SLR (including (including LAGEOS satellites) satellites) OPR free: GNSS−Sat−only (a73r6, blue) vs. GNSS−Sat + LAGEOS (A73R6, orange) 16 364.0

50.0 14 12 Amplitude GCC−Z [mm]


Impact of orbit constraints

69.0

10 8

70.2 6

87.0

38.9

182.0

4 2 0 0

50

100

150

200 Period in Days

250

300


350

400


Conclusions

SLR geocenter series are very clean for all 3 components

GNSS geocenter series for X-, Y-component are very clean

GNSS geocenter series for Z-component shows artifacts at periods related to the draconitic year

These artifacts are reduced in combined GNSSGNSS-SLR solutions, but 3rd, 5th, 7th harmonics are still present

Ignoring range biases and antenna offset corrections generates a shift and annual variations in Z-component of ~4 mm (partly also in Y-component)

The negative impact of OPR parameters on geocenter cannot be fully avoided by the inclusion of SLR data


10

∆ X (shifted +5): Mean = 0.1 mm

5

∆ GCC [mm]


Impact of atmospheric loading

∆ Y (not shifted): Mean = −0.1 mm 0

−5 ∆ Z (shifted −5): Mean = 0.2 mm −10 2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

⇒ See poster presentation by Sośnica et al.: Impact of atmospheric loading corrections on SLR and the consistency between GNSS and SLR solutions. Session G2.1, Thursday Astronomical Institute University of Bern

2011