Sentinel-3 surface topography Baseline Collection BC005: improved performance over the ocean

The Sentinel-3A/3B (S3A/B) satellites were launched in 2016 and 2018, respectively, as part of the Copernicus Program and their on-board radar altimeters provide key variables for the understanding of surface ocean dynamics and the monitoring of sea level, such as measurements of significant wave height, wind speed and sea surface height. The EUMETSAT service contract ”Copernicus Altimetry Service” (COPAS) has the goal to monitor the performance of S3 observations over ocean and validate the newly available improved products ensuring the long-term stability of the missions. Here, we provide an overview of the S3A and S3B Baseline Collection 005 (hereafter BC005) performance over the ocean compared to the previous processing baselines. Our analysis focuses on geophysical parameters such as topography, wind and waves. We used for this study mono-mission and multi-mission diagnostics, like cross-over analysis as well as comparison of maps and time series. Particular attention is given to the long-term analysis of the S3 mission performance. BC005 has become operational with the release on 9th March 2023. The new baseline provides improved sea level products and shows an overall increased quality of the observations. A full reprocessing campaign based on the new baseline collection has been completed during 2023, in order to ensure homogeneous S3A/B observations over the whole duration of both missions. BC005 brings several relevant evolutions and anomaly fixes to the S3 altimetry marine products such as correction of USO sign reading, range walk correction to SAR mode, exact dynamic zero-masking, new sea state bias correction and new GPD+ (GNSS-derived Path Delay Plus) tropospheric correction. The first two provide key improvements on the long-term stability of the S3 sea level record, rectifying the drift on global long-term trends of sea level anomaly that were previously reported for S3A/B.