Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Quality Control ofGFZ Orbit Predictions

Daniel Koenig, Roland Schmidt, Rolf Koenig

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Contents

* Characterisation of Predicted Orbits

* Quality Control* Improvement of CHAMP Orbit Predictions

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Characterisation of PDOs for CHAMP and GRACE-A/-B

True Orbit(RSO)

radial cross-track

along-track/Time Bias

3h 6h 9h ... 48h

last observation Time Advance

PDOObserved Part Predicted Part

Part of Force Function Model

Gravity of Earth Up to 05/2005: GRIM5-C1 (90x90)Since 06/2005: EIGEN-CG01C-2 (60x60)

Ocean Tides Up to 05/2005: GRIM5-C1Since 06/2005: FES2002

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Quality of Observed Part (Orbit Fit): CHAMP Laser Residuals

Change to

new gravity field

EIGEN-CG01C-2

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Quality of Observed Part (Orbit Fit): GRACE-A Laser Residuals

Change to new gravity field

EIGEN-CG01C-2

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Quality of Predicted Part: Orbit Comparison to RSOs

Satellite: CHAMPPeriod: 03/2005Component: Time BiasTime Advance: 9h

Histogram of Orbit ErrorsBetween Predicted Part and RSO

Mean : -0.57 ms Sigma : 11.64 ms Min : -32.37 ms Max : 31.42 ms Rate of inner class: 60.0 %

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Improvement of CHAMP Orbit Predictions – Results –

Satellite: CHAMP Period: 09/2004

Rate of Time Bias in [-10ms, +10ms]from Histograms

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Improvement of CHAMP Orbit Predictions – Results –

Satellite: CHAMP Period: since 05/2001 Time Advance: 9h

Rates of Time Bias in [-10ms, +10ms]from Histograms

Quality Control of GFZ Orbit Predictions

ILRS Fall 2005 WorkshopOctober 3-7, 2005, Eastbourne, UK

Summary

• Operational quality control of CHAMP and GRACE predictions by comparison to precise RSOs.

• Evaluation of orbit differences for CHAMP based on histograms for 09/2004 shows:

– that more than 90 percent of the predictions are within a time bias of [-10ms, +10ms] up to 6 hrs after the last data point, and

– that in the interval 9 to 12 hrs the aging of the predictions is most pronounced. However, still about 50 percent are within the requirement of [-10ms, +10ms] .

– Thus updating at 8h intervals (3 predicts/day) is currently still sufficient.

• On the other hand, the quality of CHAMP predictions, in particular in the critical time interval of 9 to 12 hrs after the last data point is significantly improved when exchanging the static gravity model from GRIM5-C1 to a modern GRACE-based gravity model EIGEN-CG01C-2 .