On the effect of non-tidal atmospheric and oceanic loading on the orbits of the altimetry satellites ENVISAT, Jason-1 and Jason-2

The German Research Centre for Geosciences GFZ provides non-tidal atmospheric and oceanic loading (NTAOL) displacements for tracking stations located on the Earth's surface based on ECMWF numerical weather models (NWM) and compatible with GRACE atmosphere and ocean de-aliasing products (AOD1B). We apply both, the dynamic (AOD1B) and the geometric (NTAOL) models, to Precise Orbit Determination (POD) of the altimetry missions ENVISAT, Jason-1, and Jason-2 with Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations. Alternatively to the GFZ displacements, those provided by the International Mass Loading Service (IMLS) based on the MERRA NWM are applied also. The differences in POD are qualified in terms of orbital fits, orbit differences and altimeter cross-over differences. It turns out that the major effect comes from AOD1B, that from NTAOL is considerably smaller, but visible and of benefit for POD. Long-term systematics introduced by the loading models can not be detected. Geographicaly correlated systematics important for altimetry show up, however well below the millimeter. The effect of loading on altimeter cross-over results is even smaller and close to the point where sensitivity is lost.