On the use of SWOT altimetry data for monitoring coastal hydrodynamics

• SWOT provides an effective monitoring of SWH and SSH with a standard variation less than 0.85 m. • SWOT estimates changes in SSH within a semi-open basin, at shallow areas and close to cliff coasts. • SWOT accuracy for estimating waves is ∼ 3–4 km radius and ∼ 8–12 m depth from the coastline. • Integrating SWOT 2D views is useful for monitoring the storm evolution at local scales. Satellite altimetry has proven highly effective for monitoring sea surface variability in open oceans and continental shelves, yet its extension to nearshore environments remains challenging. Within the framework of the Surface Water and Ocean Topography (SWOT) wide-swath interferometric mission, this study evaluates SWOT’s capability to retrieve coastal Sea Surface Heights (SSH) and Significant Wave Heights (SWH) in the English Channel along the UK and French coasts. SWOT 1-day Cal/Val and 21-day Science Orbit data were validated against in-situ records from 16 tide gauges and 10 wave buoys between March 2023 and July 2024, encompassing five energetic storm events. Results indicate that SWOT-derived SSH and SWH exhibit strong consistency with in-situ measurements, demonstrating high accuracy (mean RMSE ≈ 0.9), precision (mean STD ≈ 0.85), and a robust correlation (∼0.95). Agreement is influenced by the spatial offset between SWOT tracks and sensor locations, as well as by complex bathymetric and topographic conditions. A benchmarking analysis with coastal wave buoys further demonstrates reliable SWOT wave estimates within ∼ 3–4 km of the shoreline and at depths of ∼ 8–12 m. This finding underscores SWOT’s potential for monitoring shallow-water hydrodynamics and for improving the fidelity of regional and local coastal numerical models.