A new mean sea surface (MSS) was determined by focusing on the accuracy provided by exact-repeat altimetric missions (ERM) and the high spatial coverage of geodetic (or drifting) missions. The goal was to obtain a high-resolution MSS that would provide centimeter-level precision. Particular attention was paid to the homogeneity of the oceanic content of this MSS, and specific processing was also carried out, particularly on the data from the geodetic missions. For instance, CryoSat-2 and SARAL/AltiKa data sampled at high frequencies were enhanced using a dedicated filtering process and corrected from oceanic variability using the results of the objective analysis of sea-level anomalies provided by DUACS multi-missions gridded sea-level anomalies fields (MSLA). Particular attention was also paid to the Arctic area by combining traditional sea-surface height (SSH) with the sea levels estimated within fractures in the ice (leads). The MSS was determined using a local least-squares collocation technique, which provided an estimation of the calibrated error. Furthermore, our technique takes into account altimetric noises, ocean-variability-correlated noises, and along-track biases, which are determined independently for each observation. Moreover, variable cross-covariance models were fitted locally for a more precise determination of the shortest wavelengths, which were shorter than 30 km. The validations performed on this new MSS showed an improvement in the finest topographic structures, with amplitudes exceeding several cm, while also continuing to refine the correction of the oceanic variability. Overall, the analysis of the precision of this new CNES_CLS 2022 MSS revealed an improvement of 40% compared to the previous model, from 2015.

Polar sea surface height observation by radar altimeters requires missions with high-latitude orbit and specific processing to observe the sea-ice-covered region within fractures in the ice. Here, we combine sea surface height estimates from different radar satellites over the ice-free and ice-covered polar oceans to create cross-calibrated along-tracks and gridded products over the Arctic Ocean (2011–2021) and the Southern Ocean (2013–2021). The sea surface height from our regional polar products is in great agreement with tide gauges and bottom pressure recorders at monthly timescales in seasonally to year-round ice-covered regions. Thanks to the use of several missions and the mapping strategy, our multi-mission products have a greater resolution than mono-mission products. Part of the sea level variability of the Arctic Ocean product is related to the Arctic Oscillation atmospheric circulation. At long term, the Arctic altimetry sea level is coherent with in-situ steric height evolution in the Beaufort gyre, and negative sea level trends over the 10-year period are observed in the East Siberian slope region, which may be related to the local freshwater decrease observed by other studies. Our regional polar sea level products are limited by current understanding of the sea-ice lead measurements, and homogenization of these polar products with global sea level products needs to be tackled.

In the polar regions satellite sea level observations are limited by the sea ice. Thanks to a dedicated processing, sea level can however be estimated within fractures in the ice (leads) enabling to produce continuous sea level maps including the ice-covered region. Maps of sea level of the Arctic (Prandi et al., 2021) and Southern (Auger et al., 2022) ocean were produced over 2011-2021 by combining measurements of 3 satellites from 50°N/S to 88°N/S through optimal interpolation. The three satellite missions (Sentinel-3A, SARAL/AltiKa and Cryosat-2) are processed using the same standards and are in great agreement. The along-track data were ingested in the new CNES/CLS22 mean sea surface solution and in a prototype of global sea level maps. The products are provided on the Aviso Regional Products portal and serve as demonstration products for the future generation of operational CMEMS-SLTAC products. The sea level maps are validated against hourly Gloss/Clivar tide gauge at Prudoe Bay and monthly PSMSL tide gauges. It is also compared to bottom pressure recorders at the north pole and in the Beaufort sea (BGEP project) showing great correlation at monthly timescale. At inter-annual timescale, the product sea level and steric height from in-situ profiles (BGEP project) show the same evolution in the Beaufort sea. Sea level trends are also estimated from this product and compared to model trends. Arctic sea level is influenced by the atmospheric circulation. At large scale, the product sea level is correlated to the arctic oscillation index. At smaller scale in the Kara and Laptev sea regions, the product sea level is well correlated with zonal wind producing cross-shelf sea level accumulation.