CoAuthors

Nikita Zelensky (ESSIC, University of Maryland, USA); Alexandre Belli (Universities Space Research Association (USRA) @ NASA GSFC, USA); Brian Beckley (SGT Inc., U.S.A.); Douglas Chinn (SGT Inc., USA); Despina Pavlis (ESSIC, University of Maryland, USA)

Orbit error remains a major component in the overall error budget of all altimeter satellite missions. Error sources include terrestrial reference frame and station positions, systematic and unaccounted-for errors in the satellite tracking measurements, mismodeling of non-conservative forces, and incomplete modeling of time-variable gravity. The agreement between the SLR/DORIS and GPS-reduced-dynamic orbits is at the level of 6-9 mm radial RMS, however we continue to observe systematic signatures in the orbits and in the tracking data. This paper presents a status report on the development of a consistent set of new orbit standards that can be applied for the entire orbit time series, from 1992 to 2019. We have addressed three important issues: (1) adapting a new static and time-variable geopotential model to apply over the altimetry time period; (2) further improvements to the non-conservative force modeling, (3) Mitigation of the SAA effect in the Jason-2 & Jason-3 DORIS data, and the impact on the orbits and the coordinates for the DORIS stations. For the time-variable gravity modeling, the approach we have taken is to adjust a low-degree harmonic field from a large set of SLR & DORIS satellites on top of the new GRACE+GOCE a priori gravity field. Other improvements include adoption of the IERS2014 mean pole, use of the new 3-hrly AOD product developed by the GFZ for the GRACE RL06 processing. With these new set of geophysical standards, we find that RMS of fit to other altimeter satellite missions (e.g. Envisat, SARAL, HY-2A) is frequently at or below the cm level. Making an assessment of radial orbit accuracy for these non-reference mission satellites is more challenging.

We present the altimeter measurement calibration with tide gauges for the new sets of orbits for TOPEX & Jasons1-3, as well as comparisons of the GSFC orbits with those produced by other analysis centers, including the CNES, JPL, ESA, and other centers.