1. Adrian Jäggi 24th IUGG General Assembly, 02-13 July, Perugia
Assessment of GPS Observables for Gravity Field Recovery from GRACE
Adrian Jäggi
24th IUGG General Assembly, July, Perugia
Astronomisches Institut, Universität Bern

2. Recovery from LEO hl-SST Data (1)
Kinematic Orbit Positions
Pseudo-Observations with Covariance Information
Accelerometer Data
(not used)
Accelerometer Data
(not used)
Set-Up of an Orbit Determination Problem by Least-Squares
computation of the observation equations for each daily arc by numerical integration
(estimated parameters: SH coefficients, arc-specific parameters, e.g., initial conditions and pulses)
- construction of the normal equations for each daily arc
Manipulation of Normal Equation Systems
manipulation and subsequent pre-elimination of arc-specific parameters
(e.g., constraining or downsampling of pulses)
- accumulation of the daily normal equations into weekly, monthly, and yearly systems
regularization of SH coefficients
(not used so far)
inversion of the resulting normal equation systems
Manipulation of Normal Equation Systems
manipulation and subsequent pre-elimination of arc-specific parameters
(e.g., constraining or downsampling of pulses)
- accumulation of the daily normal equations into weekly, monthly, and yearly systems
regularization of SH coefficients
(not used so far)
inversion of the resulting normal equation systems
Astronomisches Institut, Universität Bern

3. Recovery from LEO hl-SST Data (2)
CHAMP Kinematic Orbits
1 year of data (DOY 071, 2002 – DOY 070, 2003)
Jäggi, A., G. Beutler, H. Bock, U. Hugentobler 2006: Kinematic and highly reduced-dynamic LEO orbit determination for gravity field estimation, in Dynamic Planet – Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic Tools, edited by C. Rizos and P. Tregoning, pp , Springer.
GRACE Kinematic Orbits
1 year of data (DOY 001, 2003 – DOY 365, 2003)
Jäggi, A., U. Hugentobler, H. Bock, G. Beutler 2007: Precise Orbit Determination for GRACE Using Undifferenced or Doubly Differenced GPS Data, Advances in Space Research, in press, available online at
GRACE Kinematic Baselines
55 days of data (DOY 243, 2003 – DOY 297, 2003)
Jäggi, A., U. Hugentobler, H. Bock, G. Beutler 2007: Precise Orbit Determination for GRACE Using Undifferenced or Doubly Differenced GPS Data, Advances in Space Research, in press, available online at
Astronomisches Institut, Universität Bern

4. Difference w.r.t. EIGEN-GL04C
Recovery from LEO hl-SST Data (3)
Difference w.r.t. EIGEN-GL04C
Observations:
30s positions
Data Period:
1 year
Accelerometer:
not used
Pulses:
15min
Astronomisches Institut, Universität Bern

5. Cumulative Geoid Height Differences (in cm) w.r.t. EIGEN-GL04C
Recovery from LEO hl-SST Data (4)
Cumulative Geoid Height Differences (in cm) w.r.t. EIGEN-GL04C
GPS Smp:
30s
Pos Smp:
L. Prange et al Gravity Field Determination at the AIUB – The Celestial Mechanics Approach
Astronomisches Institut, Universität Bern

6. GPS Carrier Phase hl-SST Observables (1)
carrier phase measurement on P1 channel
(λ = 19.0 cm) L2
carrier phase measurement on P2 channel
(λ = 24.4 cm) LA
carrier phase measurement on C/A channel
(λ = 19.0 cm, σ(LA) < σ(L1) for BlackJack receivers)
The ionosphere-free observable may be formed as L3 = α1*L1+α2*L or L3‘ = α1*LA+α2*L2 L3‘ is better for BlackJack receivers w.r.t. the noise
Astronomisches Institut, Universität Bern

7. Difference w.r.t. EIGEN-GL04C
GPS Carrier Phase hl-SST Observables (2)
Difference w.r.t. EIGEN-GL04C
Observations:
30s positions
Data Period:
1 year
Accelerometer:
not used
Pulses:
15min
Astronomisches Institut, Universität Bern

8. GRACE Carrier Phase hl-SST Observables (1)
KBR RMS:
6.38 mm
15.91 mm
Kinematic (DD, float)
Reduced-Dynamic (DD, float)
KBR RMS:
10.90 mm
20.50 mm
Kinematic (ZD)
Reduced-Dynamic (ZD)
KBR RMS:
0.88 mm
4.41 mm
Reduced-Dynamic (DD, fixed)
Kinematic (DD, fixed)
Astronomisches Institut, Universität Bern

9. Difference w.r.t. EIGEN-GL04C
GRACE Carrier Phase hl-SST Observables (2)
Difference w.r.t. EIGEN-GL04C
Observations:
varied
Data Period:
55d
Accelerometer:
not used
Pulses:
15min
Astronomisches Institut, Universität Bern

10. Difference w.r.t. EIGEN-GL04C
GRACE Carrier Phase hl-SST Observables (3)
Difference w.r.t. EIGEN-GL04C
Observations:
30s pos. diff.
Data Period:
55d
Accelerometer:
not used
Pulses:
15min
Astronomisches Institut, Universität Bern

11. GRACE Carrier Phase hl-SST Observables (4)
“normal”
KBR RMS:
14.41 mm
5.78 mm
KBR RMS:
6.10 mm
“time-differenced”
Astronomisches Institut, Universität Bern

12. Conclusions Gravity Field Recovery from CHAMP and GRACE hl-SST
data has successfully been initiated at the AIUB.
General
Results are comparable with others
LA vs. L1
LA should be used for the recovery
No improvement for low degrees
Small benefit for very high degrees
Low degrees have to be improved
Ambiguity Resolution hardly helps
Affects expectations, e.g., for SWARM
Single Satellites
vs.
Space Baseline
Astronomisches Institut, Universität Bern