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GPS-Based Precise Orbit Determination: Jason-1 Status

GPS-Based Precise Orbit Determination: Jason-1 Status. Willy Bertiger, Bruce Haines, Shailen Desai Jet Propulsion Laboratory, California Inst. of Tech., Pasadena CA Pascal Willis Institut Geographique National/Institut de Physique du Globe de Paris, France. March, 2007

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GPS-Based Precise Orbit Determination: Jason-1 Status

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  1. GPS-Based Precise Orbit Determination: Jason-1 Status Willy Bertiger, Bruce Haines, Shailen Desai Jet Propulsion Laboratory, California Inst. of Tech., Pasadena CA Pascal Willis Institut Geographique National/Institut de Physique du Globe de Paris, France March, 2007 Ocean Surface Topography Science Team Meeting Hobart, Australia

  2. Release 07a Incremetal Changes Relative to Release 06b (March 2006) • Better Understanding of GPS Phase Centers based on GRACE Dynamics and Calibrations • JEM03 – GRACE Static Gravity Field (vs GGM02C) • AOD1B Release 4 ( vs none ) • Sub-daily density variations in atmosphere, gravitational effect • ITRF2005 (vs ITRF2000)

  3. 0 mm –15 15 0 GRACE As An Antenna Instrument For GPS Trans. Calibration • Daily precise orbit solutions spanning two years (2004–06) • One s/c at a time • Dynamical POD to preserve link between scale and GM • CD and 1 cpr acc. reset every rev. per UT/CSR approach • GPS ephemeris and clock offsets fixed to precise values (JPL/IGSAC) • GRACE antenna a priori PCV model from anechoic chamber: • 30-sec GPS data • Carrier (LC) only and carrier + code (LC + PC) solutions performed. No Z apriori • Postfit residuals binned according to az/el of transmitters. • Least-squares fit to antenna map • Iterate until converged (12XLC, 5XLC/PC)

  4. Block II/IIA PCV +10 mm -10 Block IIR-B(M) PCV +18 +10 mm mm -12 -10 GRACE-Based Phase-Center Variation (PCV) Maps Reveal GPS Antenna Elements Block IIA Antenna (Mader and Czopek, 2002) Block IIR-A PCV PCV for Ionosphere-free Carrier (LC) with Mean Offset Removed

  5. T/P Radial Antenna Offset Explained

  6. JASON Calibration (3 Iterations) Code Phase mm mm -30 30 -400 400 • Dynamic JASON runs 2002-JAN-14 to 2006-JAN-01 • Very similar in appearance to release 06b (last year)

  7. Release 07a Comparison with GDRB

  8. GDRB-ITRF2000, Rel07a/GSFC-ITRF2005

  9. Reference Frame, Differences with GSFC SLR/DORIS Model Errors, GPS? Some Pattern with GDRB

  10. Geographic Radial Comparison to GDR-B Cycles 21-39 Cycles 150-169 -16 0 16 -16 0 16 mm mm RMS: 3.5 mm RMS: 1.9 mm ITRF2000 - 05 Z ~ 11.5 ITRF2000 - 05 Z ~ 5.1

  11. Geographic Radial Comparison to GSFC SLR+DORIS Cycles 21-39 Cycles 150-169 -16 0 16 -16 0 16 mm mm RMS: 3.4 mm RMS: 2.9 mm GSFC and JPL Rel07a both use ITRF2005

  12. Release 06b - Release 07a Cycles 141-146 -16 0 16 mm RMS: 1.8 mm

  13. Xover Tests

  14. Xover Tests

  15. Summary • Incremental Changes to JPL GPS orbits • Gravity Field, Phase Centers, AOD1B, ITRF2005 • Comparison with GDR-B • Close Performance Measured by crossovers • Slightly better comparison to R06b, Z shift ITRF2005 • Reference Frame Issues ~ cm (Comparison with GSFC SLR/DORIS) • Antenna, Force Models? • Future Enhancements • Use Solar Panel Quaternions to improve solar pressure • Test other gravity fields, apply time varying solid earth gravity ( fit to monthly fields ) • Improved Albedo Models • Re-tune POD strategy

  16. Backups

  17. -30 +30 mm -30 +30 Jason Phase Simulation Empirical 2XSimulation • Simulation/Limitations • Bus Structure -- Flat Plates • Other GPS Antenna -- Disk • Radiometer -- Disk

  18. GPS Transmitter PCV Maps Explain Anomalous Estimated Radial Antenna Offsets for Jason-1

  19. Improvements Over JPL Release 4, Nov. 2005 Improved Antenna, Force Models => Re-tune Stochastics, Data weight, Outlier Detection

  20. R06b Comparison to GDR

  21. Reference Frame GDRB vs Rel07b

  22. Release 06b - Release 07a Cycle Mean Z

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