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Volume 14, issue 2 | Copyright
Ocean Sci., 14, 205-223, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Mar 2018

Research article | 15 Mar 2018

Orbit-related sea level errors for TOPEX altimetry at seasonal to decadal timescales

Saskia Esselborn1, Sergei Rudenko1,a, and Tilo Schöne1 Saskia Esselborn et al.
  • 1GFZ German Research Centre for Geosciences, Department 1: Geodesy, Potsdam, Germany
  • anow at: Deutsches Geodätisches Forschungsinstitut (DGFI-TUM), Technische Universität München, Munich, Germany

Abstract. Interannual to decadal sea level trends are indicators of climate variability and change. A major source of global and regional sea level data is satellite radar altimetry, which relies on precise knowledge of the satellite's orbit. Here, we assess the error budget of the radial orbit component for the TOPEX/Poseidon mission for the period 1993 to 2004 from a set of different orbit solutions. The errors for seasonal, interannual (5-year), and decadal periods are estimated on global and regional scales based on radial orbit differences from three state-of-the-art orbit solutions provided by different research teams: the German Research Centre for Geosciences (GFZ), the Groupe de Recherche de Géodésie Spatiale (GRGS), and the Goddard Space Flight Center (GSFC). The global mean sea level error related to orbit uncertainties is of the order of 1mm (8% of the global mean sea level variability) with negligible contributions on the annual and decadal timescales. In contrast, the orbit-related error of the interannual trend is 0.1mmyr−1 (27% of the corresponding sea level variability) and might hamper the estimation of an acceleration of the global mean sea level rise. For regional scales, the gridded orbit-related error is up to 11mm, and for about half the ocean the orbit error accounts for at least 10% of the observed sea level variability. The seasonal orbit error amounts to 10% of the observed seasonal sea level signal in the Southern Ocean. At interannual and decadal timescales, the orbit-related trend uncertainties reach regionally more than 1mmyr−1. The interannual trend errors account for 10% of the observed sea level signal in the tropical Atlantic and the south-eastern Pacific. For decadal scales, the orbit-related trend errors are prominent in a several regions including the South Atlantic, western North Atlantic, central Pacific, South Australian Basin, and the Mediterranean Sea. Based on a set of test orbits calculated at GFZ, the sources of the observed orbit-related errors are further investigated. The main contributors on all timescales are uncertainties in Earth's time-variable gravity field models and on annual to interannual timescales discrepancies of the tracking station subnetworks, i.e. satellite laser ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS).

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Short summary
Global and regional sea level changes are the subject of public and scientific concern. Sea level data from satellite radar altimetry rely on precise knowledge of the orbits. We assess the orbit-related uncertainty of sea level on seasonal to decadal timescales for the 1990s from a set of TOPEX/Poseidon orbit solutions. Orbit errors may hinder the estimation of global mean sea level rise acceleration. The uncertainty of sea level trends due to orbit errors reaches regionally up to 1.2 mm yr−1.
Global and regional sea level changes are the subject of public and scientific concern. Sea...