Large scale uncertainties in sea level related to the estimation of the orbit model
As part of the ESA-CCI sea level new orbit models for ERS-1, ERS-2, Topex, Envisat, Jason-1 and Jason-2 have been estimated at GFZ. This study aims at quantifying the error of local sea level variability and trends related to the actual choice of the orbit solution. We have calculated gridded radial orbit differences from several state-of-the-art orbit models for every cycle of Envisat, Jason-1, ERS-2, and Topex, respectively. The orbit models are originating from the original geophysical data records (GDRs) and from different centers (eg. GFZ, ESOC, GSFC) and are integrated in GFZ's ADS Central system.
Main focus has been on the impact of time variable gravity field models on the orbit estimation. The variability of the radial orbit differences is large scale and seems to be connected to relative shifts of the geocenters of the orbit models. It can be described as the sum of a long term trend (up to 2.5 mm/year) and variability with peaks at frequencies of 180 and 365 days which reach ~10% of the value of the annual sea level signal. Even though the absolute numbers are small they add to the error level of local sea level trend estimations. Further studies on the impacts of additional models (e.g. troposperic models) are under way.
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Esselborn, S., Schöne, T., Rudenko, S. (2015 online): Impact of Time Variable Gravity on Annual Sea Level Variability from Altimetry. Proceedings of the IAG Symposium 2013, September 1-6, 2013, Potsdam, Germany, Vol. 143, Springer International Publishing Switzerland 2015. Available from: doi:10.1007/1345_2015_103
Rudenko, S., Dettmering, D., Esselborn, S., Fagiolini, E., Schöne, T. (2016): Impact of Atmospheric and Oceanic De-aliasing Level-1B (AOD1B) products on precise orbits of altimetry satellites and altimetry results. Geophys. J. Int., 204(3), 1695–1702, doi:10.1093/gji/ggv545
Topex: sea level differences due to orbit modelling
