SWOT in the Cryosphere: Promise, Progress, and Challenges

The SWOT mission launched in December 2022 with the goals of delivering the first global inventory of Earth's surface water, high-resolution ocean topography, and temporal variability of water bodies. Although SWOT’s primary objectives targeted terrestrial hydrology and oceanography, SWOT’s ~78° latitude orbital turnaround results in up to sub-weekly observations, unaffected by clouds, in many critical polar regions. SWOT may, therefore, also make significant contributions to cryospheric science. To capitalize on this potential, a dedicated Cryosphere Working Group was formed from the 2024 Science Team to explore and expand SWOT’s cryospheric applications. The group’s early efforts yielded the first high resolution (HR) tasking over Antarctica, adding to HR acquisitions for other key Arctic regions. Other promising advancements include a demonstration that KaRIn backscatter enables robust discrimination between sea ice and icebergs, a long-standing challenge for automated classifiers, and that the combination of sea surface height anomaly (SSHA) and backscatter supports a novel SWOT-based classification of sea ice and leads. A preliminary examination of SWOT LR data against ICESat-2 provides confidence in the feasibility of retrieving the first truly two-dimensional estimates of sea ice freeboard. SSHA observations of the Antarctic coastal margin provide, for the first time, the potential to observe variability of major surface currents across multiple timescales. HR data also provide the first frequent repeats of the 3-D structure of rifts on some Antarctic ice shelves. Additionally, the initial assessment of SWOT observations offers valuable insights into the mission’s potential for monitoring freshwater ice. Preliminary comparisons of HR PIXC data with two days of concurrent DEMs collected over river ice show ice surface elevation differences of ~25 cm. For each of these applications, however, significant challenges remain. Errors in geoid, mean sea surface, and tide corrections, and ongoing issues with crossover corrections hinder the retrieval of accurate coastal SSHA values. For ice shelves, our initial studies of HR data reveal many regions where measured elevations experience jumps, some of which may be attributed to errors in the underlying digital elevation model (DEM) from changing ice shelf fronts and rifts, and from large voids in the v1.1 100m REMA DEM. Artifacts in both HR and LR products, combined with complications introduced by onboard and ground-based processing pipelines, present further obstacles to retrieving reliable surface heights in polar regions. Ongoing work aims to resolve these issues — taking advantage of collaborations with other working groups — and establish SWOT as a powerful tool for observing cryosphere processes.

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