Early Assessment of SWOT’s Swath-mapping Capabilities over Arctic Sea Ice

Abstract

The routine measurement of sea ice, an essential climate variable, is urgently needed for improving seasonal sea ice forecasting and tracking ocean-ice-atmosphere interactions. Over the last few decades, ocean remote sensing techniques have revealed significant and rapid declines in both the extent and volume of Arctic sea ice, driven by accelerated warming at high northern latitudes. The Surface Water Ocean Topography (SWOT) mission delivers innovative wide-swath Ka-band synthetic aperture radar (SAR) interferometry and coincident Ku-band altimetry and provides, for the first time, swath mapping of sea ice from a space-based system. The novel SWOT technology can be exploited to advance knowledge of sea ice processes and properties. Although SWOT’s latitudinal limit of coverage is 78° N, this is nevertheless sufficient for mapping the seasonal sea ice zone in the Arctic which develops, grows and deforms in winter and typically reaches a maximum in the month of April. SWOT can obtain measurements across ~9-10 million square kilometers of Arctic sea ice in April. It's high-resolution swath-mapping approach captures sea ice surface topography in two dimensions, both along- and across-track. This new capability allows us to determine the areal fraction and shape of individual sea ice floes, map the 2D structure of leads, identify the ice edge location in higher fidelity than has heretofore been possible, and simultaneously measure sea ice height, from which sea ice freeboard and hence thickness may be derived. Here we show the results of our initial assessment of SWOT data collected during the 1-day fast repeat orbit phase. This particular sampling strategy allows us to track individual sea ice floes and derive high resolution estimates of ice drift velocity. SWOT backscatter signatures over sea ice are also used to discriminate between rough sea ice floes and smooth, specular  leads. We evaluate SWOT backscatter using high-resolution measurements of sea ice roughness derived from spatially-coincident ICESat-2 laser altimetry data.  We also show the feasibility of using the 2D swath-mapping capabilities of SWOT in concert with ICESat-2 sea ice height profiles to map the joint floe size-ice thickness distribution. Our results demonstrate the many benefits of swath mapping altimetry for polar sea ice studies.