Improved Non-tidal Atmospheric and Oceanic De-aliasing for GRACE and SLR Satellites

Non-tidal high-frequency atmospheric and oceanic mass variation models are routinely generated at GFZ Potsdam as so-called GRACE Atmosphere and Ocean De-aliasing Level-1B (AOD1B) products. As the barotropic ocean model PPHA used in release 0 (RL00) and 1 (RL01) has shown some deficiencies the latest versions of AOD1B are based on the baroclinic Ocean Model for Circulation and Tides (OMCT). In this chapter, we summarize the configuration and improvements of OMCT for operational AOD1B RL04 generation. As the temporal resolution of AOD1B products is 6 h and therefore S2 air tide signals may not be accounted for properly, some experiments have been made to investigate the influence of 3-hourly meteorological forcing on the resulting GRACE orbits and gravity fields. It turned out that the time-invariant atmospheric tide model used to correct interpolation errors is sufficiently accurate and even the error caused by a complete neglect of the atmospheric tides is below the current GRACE error level. Finally, the AOD1B RL04 model has been reprocessed back to 1976 for a consistent processing of SLR and subsequent combination with GRACE data. First results of LAGEOS derived C20 values with those from GRACE show higher correlations for the annual amplitudes but also semi-annual signals of unknown nature.