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

JPB 2/10 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 JPB 3/10 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 JPB 4/10 “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 JPB 5/10 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 JPB 6/10 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 JPB 7/10 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 JPB 8/10 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 JPB 9/10 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 JPB 10/10 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