Revealing Coastal Storm‐Wave Transformations From SWOT HR Observation: The English Channel Case Study

Abstract Swell propagation and transformation across variable bathymetry and coastal obstacles fundamentally control nearshore wave energy redistribution, sediment transport, and shoreline evolution. Conventional satellite altimetry cannot adequately resolve these dynamics, particularly refraction and diffraction as swell transition into shallow waters. Leveraging high‐rate (HR) observations from the Surface Water and Ocean Topography (SWOT) mission, we present the first spaceborne measurements of nearshore‐coastal wave transformation at sub‐kilometric scales. SWOT HR observations over the English Channel during Storm Mathis reveal wavelength shortening, directional shift and distinctive fan‐shaped diffraction patterns, including a 27.5° island‐induced diffraction signal undetected by operational models. Comparisons with in situ measurements and the Atlantic‐European Northwest Shelf (NWShelf) Reanalysis, a regional configuration of the WAVEWATCH III spectral wave model, validate the robustness of the SWOT‐derived wave parameters. This finding establishes SWOT HR data as a new observational capability for quantifying wave‐bathymetry interactions and the resultant redistribution of wave energy that conventional altimetry fails to resolve.