Beyond Coastal Validation: Resolving Storm-Time Sea Surface Height Variability with SWOT High-Resolution Observations

Coastal water levels during storms result from interacting tides, storm surges, waves, currents, bathymetry, and coastal geometry, producing spatially heterogeneous responses that remain difficult to characterize from point observations alone. The Surface Water and Ocean Topography (SWOT) mission provides a new opportunity to investigate this complexity through wide-swath High-Resolution (HR) observations of sea surface height (SSH). Here, SWOT HR water levels are first evaluated against five tide gauges in the English Channel and subsequently analyzed at three contrasting sites, Cherbourg, Villers-sur-Mer, and Étretat, using complementary spatial and scale-resolved approaches. SWOT HR shows strong agreement with tide gauges at the best-performing sites, with RMSE values of approximately 0.11 m and correlations exceeding 0.99, while accuracy remains site-dependent. Beyond point-based validation, the two-dimensional HR fields reveal pronounced spatial heterogeneity, including localized and elongated SSH anomalies with distinct geometries and orientations. EOF decomposition shows that more than half of the variance remains beyond the first six modes at all three sites, highlighting the complexity of the HR spatial signal. The detrended SSH anomalies show organized spatial patterns, while their point-by-point linear correlations with radar backscatter (σ0) remain close to zero. Across the three investigated coastal domains and two storm events, the two-dimensional wavelet analysis identifies enhanced SSH variability within an energetic scale range of approximately 0.5–1.0 km, although its intensity, spatial distribution, and organization differ substantially among sites. Comparison with independent wave, surface-current, and bathymetric fields further places these observations within contrasting hydrodynamic and morphological environments, suggesting that the observed sub-kilometer SSH variability may be associated with local coastal processes, although their individual contributions remain unresolved. . Together, these analyses demonstrate the added value of SWOT HR for resolving the two-dimensional, multiscale complexity of storm-time coastal SSH, providing new spatial information for investigating coastal dynamics and supporting high-resolution model validation and data assimilation.