Improved inter-calibration of multi-mission altimeter significant wave heights for climate data record

With 30 years of uninterrupted observations and more than 15 successful missions, satellite altimetry is a mature technology for investigating sea state variability at decadal timescales with global coverage. However, deriving robust long-term statistics from multi-mission products requires careful processing of each mission product in order to ensure inter-mission consistency and long-term stability. Over the last three years, the ESA Sea State Climate Change Initiative has been performing a full reprocessing of the SGDR products from Jason-1, ENVISAT, Jason-2, Cryosat-2, SARAL, and Sentinel-3A. This reprocessing benefits from recently developed waveform retrackers, consistent data editing and inter-calibration methods and an adaptive denoising approach designed for the analysis of non-stationary and non-linear signals. In this study, we present the method to calibrate the Jason-2 reference data against in situ observations and inter-calibrate the other missions using comparisons with this reference at crossover ground points. The validation of the results uses in situ observations, model results from ERA-5 reanalysis and WW3-IFREMER hindcast, and cross-comparisons of independent missions . A particular focus is given on the coastal zone and on low and extreme sea state data in order to discuss the performance of this new altimeter product with respect to standard products provided by the space agencies.