POD/Geoid splinter

1. POD/Geoid splinter March 14, 2007 J.P. Berthias Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

2. Venice OSTST 2006 POD/Geoid splinter summary • Very good agreement between all orbits (CNES, JPL, GSFC, CSR) • Periodic Z-shifts between GPS and DORIS/SLR orbits • expected origin was incoherence between reference system of the three tracking techniques • Good convergence on standards to start producing orbits with new standards by Fall’06 • assumed availability of ITRF2005 and time variable gravity model by mid-2006 • Choice of geoid model (EIGEN-GL04C) Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

3. GDR-b reprocessing • ITRF2005 evaluation revealed problems with SLR • adoption of ITRF2005 in Fall’06 but expected convergence between tracking systems not satisfactorily achieved • Decision to reprocess early Jason-1 cycles with GDR-b standards • as a consequence the switch to the new standards (GDR-c standards) is postponed to the end of 2007 • new goal is to define standards which will be used by Jason 1 and 2 • note: GDR-b models predate the Venice OSTS meeting • Opens the possibility to revise the “Venice” standards • newer generation GRACE Gravity and Geoid models ? • new models for Time Variable Gravity ? • corrections to ITRF2005 ? • various enhancements to other models ? Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

4. “Venice” standards • Models based principally on IERS2003 standards • GRACE based gravity model : EIGEN-GL04C • Tide model FES2004 with correction to K2 wave • ITRF2005 checked and “corrected where needed” • GPS orbits and clocks • JPL ITRF2005 orbits and clocks • JPL antenna maps for Jason and GPS constellation • Data combination DORIS+SLR+GPS • Appropriate level of parametrization • green color indicates standard implemented in GDR-b, red indicates not implemented Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

5. Standards as of Venice OSTS meeting (continued) • Geocenter motion (not applied for lack of consensus model) • Time Variable Gravity (atmosphere, hydrology) • models remained TBD • Solar radiation pressure modeling • still undecided between UCL and scaled box+wing model • Laser reflector array correction • to be confirmed • SAA model for DORIS • thermal emission forces • evidence of incoherencies between “physical” and “observed” values Note: GDR-b uses SAA model until cycle 90 not later Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

6. What the “Tasmanian” standards could be … • IERS2003 standards with ocean pole tide model • GRACE based gravity model with C21/S21 and rates set to IERS2003 values • Tide model FES2004 with corrected K2 wave • ITRF2005 checked and “corrected where needed”, with updated station weights and biases • ITRF 2005 GPS orbits and clocks from JPL • Time Variable Gravity (atmosphere, hydrology) based on meteorological data and annual/semi-annual low degree expansion • Solar radiation pressure modeling with modified box+wing model ? • Laser reflector array elevation dependant correction ? • SAA model for DORIS • thermal emission forces based on “observed” values ? • Data combination DORIS+SLR+GPS for GDR • but provide also DORIS+SLR solution for tandem phase ? Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

7. Practical goals for POD/Geoid splinter • Evaluate quality of delivered orbit products (GDR-b) • Evaluate impact of ITRF2005 and adopt it as a reference for Jason • review SLR scale factor issue • propose corrections for DORIS and SLR • Review of progress on Gravity and Geoid models • Review available TVG models and discuss implementation issues • Review of progress on other models • Review contribution of orbit to the overall error budget • Collect inputs on the Jason-3 orbit choice issue from the POD point of view Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

8. Morning session – first half (Tasman A) • 09:30 - J.-P. Berthias - Introduction:Status of Pending Actions and Key Issues • 09:45 - L. Cerri - Jason-1 POD Reprocessing at CNES: Current Status and Further Developments • 10:00 - L. Cerri, J.-P. Berthias – Time Variable Gravity : Implementation Issues for Jason 1 • 10:15 - W. Bertiger - Precision Orbit Determination, Trade Studies and Improvements for Jason-1 with GPS • 10:30 - Break Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

9. Morning session (Tasman A) • 11:00 - F. Lemoine - Improvement of the Complete TOPEX and Jason Orbit Time Series: Current Status • 11:15 P. Bonnefond - Validation Activities for Jason-1 and Topex/Poseidon Precise Orbit • 11:30 - J. Ries - Orbit Error Budget for Jason-1 and Topex/Poseidon Precision Orbits • 11:45 - Ch. Foerste - On the use of Temporal Gravity Field Models Derived from GRACE for Altimeter Satellite Orbit Determination • 12:00 - P. Willis - Validation and Extension of ITRF2005 for DORIS POD • 12:15 - J. Ries - Validation and Extension of ITRF2005 for SLR POD Ocean Topography Science Team Meeting - Hobart, Australia – March 2007

10. Afternoon session (Tasman A) • 16:30 - Discussion on key POD Issues: ITRF2005 implementation, time variable gravity, other model recommendations • 17:00 - J. Ries GRACE Mission Status and Current Results • 17:15 - R. Biancale EIGEN5 activities at GFZ and GRGS • 17:30 - X. Deng Assessment of Geoid Models off Western Australia Using Oceanographic In-Situ Measurements • 17:45 - M.-H. Rio Ocean Mean Dynamic Topography from Altimetry and GRACE: Toward a Realistic Estimation of the Error Field • 17:55 - Discussion on remaining Geoid Issues • 18:00 - Adjourn Ocean Topography Science Team Meeting - Hobart, Australia – March 2007