Wide-Swath Mapping of Antarctic Sea-Ice Height and Freeboard From SWOT Ka-Band Interferometry: Comparison Using ICESat-2

Abstract

The surface water and ocean topography (SWOT) mission provides Ka-band wide-swath interferometric altimetry, enabling two-dimensional (2-D) observations of polar sea ice. This study presents one of the first large-scale Antarctic assessments of SWOT-derived sea-ice surface height and freeboard through near-coincident comparison with ICESat-2 laser altimetry across multiple sea-ice sectors and seasons. Sea-ice surface height relative to the DTU21 mean sea surface shows strong spatial consistency with ICESat-2 ATL07 across 130 spatiotemporally collocated regions, yielding a mean absolute error (MAE) of 0.13 m and a correlation coefficient of 0.84 at 500 m resolution. SWOT-derived freeboard, retrieved using an adaptive-window inverse-distance-weighting reconstruction of the lead-referenced local sea surface, shows moderate consistency with ICESat-2 ATL10 total freeboard, with a negative bias of −0.07 m and an MAE of 0.11 m. A systematic variation of SWOT–ICESat-2 freeboard differences is observed across different freeboard regimes, with larger negative differences occurring at higher freeboard values, likely reflecting the combined effects of scale-dependent spatial representation, local sea-surface reference uncertainty, and radar–laser measurement differences. Overall, these results demonstrate that SWOT provides spatially coherent, 2-D wide-swath observations of Antarctic sea-ice freeboard, complementing the high-precision but along-track sampling of ICESat-2 and supporting improved characterization of mesoscale sea-ice variability.