Denise Dettmering (DGFI-TUM, Germany); Maria Pisareva (DGFI-TUM, Germany)

In the framework of the SWOT Science Team project "SWOT for Marine Applications in the Polar Seas (SMAPS)" SWOT’s capabilities for sea surface height (SSH) determination in the ice-covered ocean up to a latitudinal limit of 78°N are assessed. In the case of the Arctic Ocean, the SWOT L2 LR Unsmoothed swath observations represent the predominant observation mode and will be used from the end of March 2023 to the end of April 2024. In order to assess the quality of the novel 2D-SSH data, they are compared with laser altimetry observations from ICESat-2. The comparison is carried out based on sea level anomalies (SLA). To ensure the most coherent assessment possible, both datasets are referenced to the same mean sea surface (i.e., DTU21), and consistent geophysical corrections are applied as far as possible. The greatest challenge, however, is to find simultaneous measurements of overlapping areas. This is particularly important in the sea-ice covered ocean because of rapidly changing sea ice conditions within a few hours. For this reason, a maximum acquisition time gap of 30 minutes has been set, leading to about 550 suited Arctic-wide crossover locations. In the next step, the SWOT wide-swath data is interpolated to ICESat's individual laser beams, enabling point-by-point quantitative comparisons. Moreover, visual comparisons with Sentinel-1 radar images are performed in order to evaluate the extent to which sea ice surface features, such as ice floes or leads, are mapped by SWOT. Different spatial resolutions are considered by applying spatial low-pass filtering to ICESat-2 and Sentinel-1.
For all crossover locations, point-by-point comparisons are performed, and statistical analyses of the differences are conducted. In general, the differences in SLA show a mean standard deviation of 8 cm when taking all surface conditions into account and 6 cm by limiting the pointwise comparison to open water (i.e., leads). Discrepancies, resulting from the SWOT internal cross-correction, may cause significant height deviations of tens of centimetres between the left and right SWOT swath. Visual comparisons clearly show good accordance between minimum heights and dark pixel values, indicating leads and open water spots. Limitations can be found in the representation of smaller ice-floes or narrow leads, and ridges not showing clear height variations in the swath data.