Jason-2 geographically correlated radial orbit difference 365-day signals of DORIS-only dynamic (left) and reduced-dynamic (right) orbits when including or not Ries annual geocenter model.
Based on experience gained with the past altimeter missions initiated by TOPEX/Poseidon and continued through Jason-1, Envisat, and with the currently flying satellites Jason-2 (OSTM), CryoSat- 2, HY-2A, SARAL, Jason-3, Sentinel-3A (soon Sentinel-3B, Sentinel-6/Jason-CS, SWOT ...), for which we deliver precise and homogeneous orbit solutions, we propose to:
- assess quality by taking advantage of the three high precision tracking systems operating on the Jason-series missions (GPS, DORIS, and SLR);
- compute precise orbits for all three satellites (Jason-1, OSTM/Jason-2 and Jason-3) with state of the art force and geometric models;
- examine force and measurement modeling improvements: improved surface force models (Solar Radiation Pressure (SRP) and thermosphere models), new GRACE-based mean geopotential models. For GPS, new and promising results are expected on Jason-3 as the integer ambiguity fixing seems possible;
- accurately determine the gravity changes at low spherical harmonic degrees making the most of all available space geodetic techniques (GRACE, EOP, SLR, GNSS, DORIS, …): this requires improving the consistency of methods to solve for the variations of the three degree-1 coefficients (geocenter motion), i.e. look for strategies that mitigate sensitivity to miscentering effects on the orbit coming from the tracking measurements, and the spherical harmonic degree 2;
- characterize systematic errors in laser observation through precise orbit determination on the geodetic satellites (Lageos-1/2, Starlette, Stella, Lares) and possible alternative methods (e.g. using mascons based on multi-missions DORIS measurements);
- detect geographically correlated orbit errors using the laser-based short-arc technique;
- characterize orbit errors through the computation of altimeter sea level differences at crossovers, the Sea Surface Height (SSH) cross comparison between Jason missions, other altimeter missions, and in situ measurements (Argo floats);
- periodically define and produce an updated set of orbits and geophysical standards to address short-term and long-term orbit errors impacting mean sea level change estimates.