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, 02-13 July, Perugia Astronomisches Institut, Universität Bern

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

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. 354-361, 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 http://dx.doi.org/10.1016/j.asr.2007.03.012. 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 http://dx.doi.org/10.1016/j.asr.2007.03.012. Astronomisches Institut, Universität Bern

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

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

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*L2 or L3‘ = α1*LA+α2*L2 L3‘ is better for BlackJack receivers w.r.t. the noise Astronomisches Institut, Universität Bern

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

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

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

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

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

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