CoAuthors

Nikita Zelensky (University of Maryland, USA); Brian Beckley (SGT/GSFC, USA); Douglas Chinn (SGT / GSFC, USA); Alexandre Belli (NASA/GSFC, USA); Despina Pavlis (UMD / GSFC, 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. We have updated and replaced the previous orbit series that we distributed to the NASA Measures program to be part of the Altimetry Climate Data Record (Beckley et al., 2017), std1504_dpod. This paper describes the new orbit series. We have addressed several important issues, including (1) adapting a new static and time-variable geopotential model to apply over the altimetry time period; (2) applying further improvements to the non-conservative force modeling, (3) mitigating 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 the IERS2014 mean pole, using he new 3-hrly AOD product developed by the GFZ for the GRACE RL06 processing, and elevation-dependent weighting for the DORIS data.

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 new GSFC orbits (std2006) with the CNES POEF, and the JPL/GPS Reduced-dynamic series of orbits. As a reminder, whereas the GSFC orbits use SLR and DORIS data, the JPL orbits only use GPS, and the CNES orbits use both GPS and DORIS data. Whereas the previous series (std1504_dpod) had an RMS radial agreement with POEF of 7-9 mm over 166 cycles of the Jason-3 mission, the new series has an RMS radial orbit agreement of 5-7 mm. Thus, the indications are that we have achieved a notable improvement in the quality of the satellite orbit products. In addition, we show a remarkable convergence in orbit modeling by the different geodetic techniques even in advance of the development of the new ITRF2020.