Contribution of DORIS in Unveiling Systematic Errors in Altimeter Satellites' Precise Orbits

The continuous record of sea surface height measurements was initiated in 1992 by the TOPEX/Poseidon (NASA/CNES) mission and continued in 2001, 2008 and 2016 with the successive launches of the reference Jason-1 (CNES/NASA), OSTM/Jason-2 and Jason-3 (CNES/NASA/EUMETSAT/NOAA) satellites, respectively. The complementary missions Envisat and CryoSat-2 (ESA), HY-2A (CNSA), Saral/AltiKa (ISRO/CNES), Sentinel-3A/B (ESA) fly in different orbits with lower altitudes and higher inclinations. This altimeter constellation of 10 satellites will keep expanding in the future with the extension of the three families Jason-CS, Sentinel-3 and HY-2 with 11 more satellites by 2030, not counting the next generation radar altimeter U.S.-French SWOT mission. All these Low-Earth Orbiters (LEOs) are at least equipped with a DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) receiver in addition to a laser retroreflector array, and most of them also carry a GPS (Global Positioning System) dual-frequency receiver, to support their Precision Orbit Determination (POD) requirements.The CNES POD group delivers homogeneous precise orbit solutions for these independent altimeter missions. This paper presents our plans for updating our POD standards and investigating improvements to modeling or mitigating remaining sources of orbit error. In particular, we show results from independent validation of SLR station biases, long-wavelength time-variable gravity recovery before the GRACE era, as well as geocenter motion determination, leveraging the long-time history of LEO satellites that are tracked using DORIS measurements.