Sentinel-6 PDAP products assessment over ocean

Launched on 21 November 2020, Sentinel-6 Michael Freilich is a Copernicus satellite designed to ensure the continuity to the mean sea level climate time series measured by the TOPEX/Poseidon and Jason satellites since 1992. The main payload carried on-board Sentinel-6 is the Poseidon-4 (POS4) dual frequency radar altimeter. POS4 uses an approximate9 kHz Pulse Repetition Frequency, and an innovative interleaved chronogram allowing for the optimization of the number of measurements acquired. Thanks to the interleaved design, POS4 offers for the first time the possibility to downlink simultaneous: Low Resolution (LR) data aiming at extending the legacy of the mean sea level record, and High Resolution (HR) or Synthetic Aperture Radar (SAR) data that significantly improves the along-track spatial resolution and reduces measurement noise. The on-board Range Migration Correction (RMC) algorithm , another innovation of POS4, allows reducing the HR data volume by half, in turn it facilitates the downlink of both LR and HR data all over the Globe. In this presentation we focus on the altimetry products from baseline F06, both the NRT/STC/NTC data disseminated by the EUMETSAT PDAP ground segment, as well as the full mission reprocessed data of the same baseline produced by EUMETSAT. All the NRT/STC/NTC timeliness products are assessed, and particular attention is given to the quality assessment of the NTC and reprocessed products. Both LR and HR performances are addressed. Moreover, POS4 instrument performances from the PDAP Long Term Monitoring are briefly summarized. For all latencies, LR requirements are fulfilled and data products show good continuity with Jason-3. GMSL inter-mission bias is well characterised after about 12 months, and GMSL continuity with Jason-3 is illustrated, although a longer time series is needed to fully demonstrate this. It is also shown that HR requirements are met for all latencies, except for SWH that are overestimated at high wave heights due vertical wave velocity impacts (a known issue in SAR altimetry) even after the number of looks was reduced in baseline F06. HR RMC is also assessed and presents performances very similar to the HR RAW data performances over open ocean, and in coastal regions.