Abstract
By convention the absolute bias in sea surface height (SSH) is the difference between the altimeter and the in-situ reference SSH heights above the Earth ellipsoid. Both the absolute and the relative bias of the CryoSat-2 and Sentinel-3A missions are derived in this study at four stations along the German coasts.
Firstly, the coastal data processed in Delay Doppler altimeter (DDA) mode, also called SAR mode (SARM), are shown to be less noisy than data in pseudo-low resolution mode (PLRM), which is comparable to the conventional low-resolution mode (LRM). The best agreement with in-situ data is reached by the SARM data retracked with the SAMOSA+ coastal retracker (hereafter SAR/SAMOSA+) from the ESA GPOD SARvatore service.
Secondly the absolute bias and its standard deviation are computed for each mission and product type. The mean mission absolute bias depends on location and altimeter product. Both the absolute and relative biases are small and the standard deviation is smaller than 4 cm and larger than the bias. Departures between absolute biases evaluated at different stations are possibly related to geoid inaccuracy in the coastal zone. Finally, the smaller standard deviation of the bias time series confirms that SAR altimetry is more accurate than PLRM, the minimum standard deviation is 2 cm.
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Acknowledgements
The authors acknowledge EUMETSAT, the European Space Agency (ESA) and the ESA/ESRIN G-POD team for the CryoSat-2 and Sentinel-3A data products. In-situ data are kindly provided by the German Waterway and Shipping Administration (WSV) and by the German Federal Institute of Hydrology (BfG). Local geoid GCG2016 and GPS coordinates were make available by the Federal Agency for Cartography and Geodesy (BKG). We acknowledge the German Federal Maritime and Hydrographic Agency (BSH), the Deutscher Wetterdienst (DWD), the European Centre for Medium-range Weather Forecasts (ECMWF) for providing model data. Support to the first author was partly provided by ESA in the frame of the Sea Level Climate Change Initiative (SLCCI, ESA Contract N.4000109872/14/I-NB), the GOCE++ DYnamic COastal Topography and tide gauge unification (GOCE/Dycot, ESA Contract N.4000114331/15/NL-FF) and the SAR Altimetry Coastal and Open Ocean Performance (SCOOP, ESA Contract 4000115385/15/I-BG) projects. We are also grateful to the editor and to the two anonymous reviewers who helped to improve the manuscript.
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Fenoglio, L. et al. (2019). Calibrating CryoSat-2 and Sentinel-3A Sea Surface Heights Along the German Coast. In: Mertikas, S., Pail, R. (eds) Fiducial Reference Measurements for Altimetry. International Association of Geodesy Symposia, vol 150. Springer, Cham. https://doi.org/10.1007/1345_2019_73
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DOI: https://doi.org/10.1007/1345_2019_73
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