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Precise orbit determination for GRACE using undifferenced or doubly differenced GPS data

This paper discusses the use of undifferenced or doubly differenced GPS data for precise orbit determination of the GRACE satellite mission. The study explores different processing strategies and solutions, including float and fixed processing, separate and combined processing, and the effects of ambiguity fixing on the relative GRACE positions. The results show improved orbit determination and potential for optimizing the solutions.

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Precise orbit determination for GRACE using undifferenced or doubly differenced GPS data

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  1. Precise orbit determination for GRACE usingundifferenced or doubly differenced GPS data Adrian Jäggi 36th COSPAR Scientific Assembly, 16-23 July, Beijing

  2. GRACE Processing Strategies • - ZD Solutions • - DD Solutions • float / fixed Separate Processing Combined Processing • - DD Solutions • space baseline only • all baselines • float / fixed

  3. GRACE A Pseudo-Stochastic GRACE Orbit Modeling Observations • GPS observations of GRACE A+B and IGS stations CODE AC products • GPS final orbits and high-rate clock corrections • Station coordinates and troposphere estimates GFZ Gravity Field Model • EIGEN-CG03C Orbit Determination • Reduced-dynamic batch least-squares • Piecewise constant accelerations (over 6 min) • (Instantaneous velocity changes (every 6 min)) • Kinematic batch least-squares

  4. GRACE ZD Results GRACE A SLR RMS: 2.43 cm GRACE B SLR RMS: 2.37 cm

  5. KBR RMS: 12.2 mm 10s Sampling 30s Sampling . EIGEN-CG03C o EIGEN2 KBRR RMS: 15.9 um/s GRACE ZD Results K-Band Range K-Band Range-Rate

  6. GRACE DD Processing (with Ground Net)

  7. Ambiguity fixing on the space baseline significantly improves the relative GRACE positions, but the displayed solutions are not (yet) fully optimized. GRACE DD Results (with Ground Net) K-Band Range KBR RMS: 11.3 mm 10.8 mm 10.2 mm 3.1 mm Separate Processing • ZD float • DD float Combined Processing • DD float • DD fixed (space baseline)

  8. GRACE DD Results (with Ground Net) GRACE A SLR RMS: 2.21 cm 2.20 cm 2.20 cm 2.03 cm GRACE B SLR RMS: 1.88 cm 1.83 cm 1.87 cm 1.81 cm

  9. GRACE DD Results (with Ground Net) Orbit Differences w.r.t. DD float ZD float DD float DD fixed anti-correlated oscillation anti-correlated offset

  10. K-Band Range Ambiguity fixing on the space-ground baselines significantly improves the relative GRACE positions, even if only 47.1% of all ambiguities could be fixed. GRACE DD Results (with Ground Net) K-Band Range KBR RMS: 10.3 mm 3.4 mm Separate Processing (no space baseline!) • DD float • DD fixed (space-ground baselines)

  11. Ambiguity fixing on the space baseline and relative constraining of GRACE A and B accelerations yields optimal baseline results. GRACE DD Tuning (Space Baseline only) K-Band Range KBR RMS: 1.39 mm 1.03 mm 0.80 mm Experimental Test Solutions • 06-min accelerations („abs“, „abs+rel“ constraints) • 60-min accelerations

  12. KBR RMS: 0.88 mm accelerations pulses KBR RMS: 4.41 mm GRACE DD Results (Space Baseline only) Reduced-Dynamic (fixed) Kinematic (fixed)

  13. GRACE DD Results (Space Baseline only) Reduced-Dynamic (float) KBR RMS: 6.38 mm Zero Difference KBR RMS: 10.90 mm

  14. Conclusions ZD Solutions • Attractive for single low Earth orbiters • (2.4 cm SLR and 12.2 mm KBR RMS for GRACE) DD Solutions (Ground Net) • Similar performance as ZD solutions • Attractive to include the space baseline • Ambiguity fixing improves the rel. orbit • (probably also the absolute orbits) DD Solutions (Space Baseline) • Attachment to „any“ orbit may be done • Ambiguity fixing improves the rel. orbit • (0.88 mm KBR RMS with relative constraints) Open Issue • Shift in cross-track (float / fixed)

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