DUACS DT2021 reprocessed altimetry improves sea level retrieval in thecoastal band of the European seas

More than 29 years of altimeter data have been recentlyreprocessed by the multi-satellite Data Unification and AltimeterCombination System (DUACS) and made available under the name of DT2021 through the Copernicus Marine Service (CMEMS) and the CopernicusClimate Change Service (C3S). New standards have been applied and variousgeophysical correction parameters have been updated compared to the previousrelease in order to improve the product quality. This paper describes the assessment of this new release through thecomparison of both the all satellites and the two satellites product with external in situ tide gaugemeasurements in the coastal areas of the European seas for a time periodfrom 1 January 1993 to 31 May 2020. The aim is to quantify theimprovements on the previous DT2018 processing version for the retrieval ofsea level in the coastal zone. The results confirmed that the CMEMS product in the new DT2021 processingversion better solves the signal in the coastal band. The all satellites dataset showed areduction of 3 % in errors when compared with tide gauges and of 5 % inthe variance of the differences between the datasets compared to DT2018reprocessing. Moreover, the all satellites dataset provided more accurate sea levelmeasurements when making a comparison with tide gauges with respect to the climatic two satellitesdataset due to the better performance of the former for the assessment ofhigher than climatic frequency signals. By contrast, the two satellite dataset is themost suitable product for the assessment of long-term sea level sea surface height (SSH) trendsin the coastal zone due to its larger stability to the detriment of the all satellitesdataset.