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Improvement of a Complete and Consistent TOPEX and Jason Orbit Time Series

Improvement of a Complete and Consistent TOPEX and Jason Orbit Time Series. GSFC Altimetry/POD Group F.G. Lemoine, N.P. Zelensky, S.B. Luthcke, D.D. Rowlands, B.D. Beckley, D.S. Chinn OSTST Meeting March 12-15, 2007 Hobart, Tasmania. Outline. Status

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Improvement of a Complete and Consistent TOPEX and Jason Orbit Time Series

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  1. Improvement of a Complete and Consistent TOPEX and Jason Orbit Time Series GSFC Altimetry/POD Group F.G. Lemoine, N.P. Zelensky, S.B. Luthcke, D.D. Rowlands, B.D. Beckley, D.S. Chinn OSTST Meeting March 12-15, 2007 Hobart, Tasmania

  2. Outline • Status • ITRF2000 / ITRF2005 Comparisons & Validation. • Jason DORIS SAA Correction & Impact. • Jason Solar Radiation Pressure (SRP) model tests • Summary

  3. Status • We have completed and delivered a consistent time-series of ITRF2000 and ITRF2005-based SLR/DORIS dynamic orbits for TOPEX/Poseidon & Jason-1: • Jason-1 cycles 1-183 ; 01/15/02 - 01/03/07 • TOPEX cycles 1-481; 09/25/92 - 10/09/05 • TOPEX SLR/DORIS orbits cycles 1-364, 365-446 Tandem • TOPEX SLR/Crossover orbits cycles 447-481 Tandem • The TOPEX orbits used by Phil Callahan for GDR reprocessing (“tvg_dyn_2006aug28”) are based on ITRF2000 and other modelling improvements. • These orbits are not the GSFC final product. • ITRF2005-based orbits are preliminary and will soon be updated.

  4. TOPEX/Jason GSFC Modeling Improvements

  5. Grace-derived time-variable gravity to 20x20 (annual terms only) • Monthly solutions from KBRR data only • Fit mean, trend, & annual harmonic • 2 solutions: 1-yr & 3-yr data span Reference: ‘Monthly spherical harmonics gravity field solutions determined from GRACE inter-satellite data alone,’ Luthcke et al., Geophyscal Research Letters, 2006.

  6. Jason-1 Tracking Data Summary Statistics Cycles 008-020 Evaluation Period

  7. Evaluation of new Jason orbits based on ITRF2005

  8. Evaluation of new TOPEX orbits based on ITRF2005

  9. TOPEX Radial Orbit Difference Trends (ITRF2005 – GDR (CSR95)) Geographically correlated error (GGM02C-JGM3) Annual signal amplitude (TVG annual – none)

  10. Long-term Orbit Error and the Terrestrial Reference Frame (TRF) Jason (and TOPEX) radial orbit differences are driven by the difference in Z

  11. TOPEX Radial Orbit Difference Trend ITRF2005 – GDR (CSR95) Consequent error in estimated regional and global MSL trends

  12. Jason GSFC TRF orbit trends

  13. Jason TRF orbit trends – JPL GPS

  14. Jason DORIS SAA correction

  15. Jason DORIS SAA correction: Comparison of SLR/DORIS & SLR/Crossover Orbits ~ 0.9 mm oscillator jump at cycle 91

  16. Jason DORIS SAA correction

  17. Jason Macromodel Scaling

  18. Jason SRP Model

  19. Jason SRP Model

  20. Jason SRP Model 120-day radial difference amplitude (mm) SLR/DORIS (CR=1) – (CR=0.914) orbits SLR/DORIS (CR=1) – JPL GPS6b orbits

  21. POD Summary => Latest and most accurate available GSFC orbits ensure a uniform and accurate reference frame over 14 - years of Topex and Jason altimeter measurements, and show significantly improved DORIS, SLR, and altimeter crossover residuals. Consistency across missions is vital. => Orbit error due to Terrestrial Reference Frame (TRF) Z-drift directly affects MSL trend estimates on the order of 0.2-0.4 mm/year overall, and up to 1-2 mm/year regionally. Tests show ITRF2005 is the best TRF to date. => Latest model and method refinements anticipate a further improved orbit time series which will be generated upon completion of testing.

  22. Current and Future Efforts • =>Several models continue to be refined and tested • • Finalize ITRF2005 SLR/DORIS complement (multi-center effort) • • Revisit SLR bias management and TOPEX LRA correction • • Mean and Time varying gravity derived from GRACE and SLR. • • DORIS SAA correction for Jason (?). • • UCL radiation surface force model for Jason. • • Atmosphere loading. • • Ocean pole tide model. • • GPS ITRF2005 issues and JPL GPS phase center maps • • GPS processing enhancements (e.g. single difference, undifferenced, improved bias handling …). • =>Additional complete and consistent orbit time series: • • Jason-1 GPS and GPS+SLR reduced dynamic orbits. • • TOPEX and Jason-1 SLR+DORIS reduced-dynamic orbits.

  23. Access to GSFC 2007 orbits The orbits are available on our anonymous ftp account in Unix compressed POE format. anonymous ftp dirac.gsfc.nasa.gov ITRF2000 TOPEX and Jason orbits: pub/earth/repro_topex/tvg_dyn_2006aug28/ gsfc_poe_dyn_tvg.$cycle.Z TOPEX (cycles 1-481) pub/earth/repro_jason/swt07/ gsfc_poe_dyn_saa.$cycle.Z Jason (cycles 1-183) The ITRF2005 and ITRF2005s (SLR rescaled) orbits are preliminary and will be updated: pub/earth/repro_topex/preliminary/ gsfc_poe_itrf2005_only.$cycle.Z TOPEX (cycles 1-481) gsfc_poe_itrf2005s_only.$cycle.Z TOPEX (cycles 1-364)   pub/earth/repro_jason/preliminary/ gsfc_poe_itrf2005_only.$cycle.Z Jason (cycles 1-183) gsfc_poe_itrf2005_only.$cycle.Z Jason (cycles 1-183)

  24. Backups

  25. Jason TRF orbit trends – CNES GDRB

  26. Jason-1 radial trend: SLR/DORIS (gsfc), vs. GPS(jpl). No modelling of COM in SLR/DORIS orbits. Include modelling of COM in SLR/DORIS orbits.

  27. GPS orbits for Jason-1 are based on GPS satellite orbits which are computed as free network solutions, and rotated to ITRF2000. SLR/DORIS orbits are computed using position & velocities fixed in ITRF2000. Therefore Jason-1/GPS orbits follow more closely the COM (geocenter), whereas the SLR/DORIS orbits are more COF. Lesson: Be consistent! Be careful when you create a sea level time series. Account for COM! Jason-1 radial orbit difference trend SLR/DORIS (gsfc), vs. GPS(jpl) Why do these differences occur? Why do we care?

  28. Orbit consistency across missions Jason-1 - TOPEX Mean SSH Improved agreement over Jason-1Verification period, seen in upper right image results from improved TOPEX and Jason-1 orbits. Improvement was realized by using the more current ITRF2000 reference frame and associated station complement in the orbit computations, the GGM02C gravity field, and other improved force and measurement models.

  29. TP/Side A TP/Side B Jason-1 ITRF2000 CSR95L02 Improvement in orbit accuracy and consistency across missions is critical to long-term sea level studies … Geophysical modeling and the Reference Frame are two issues that are critical to this problem.

  30. Topex/Poseidon Orbit Performance Summary: Cycles 1-446

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