SWOT based intertidal topography mapping: A standalone method validated in a complex coastal region

The Surface Water and Ocean Topography (SWOT) satellite altimetry mission, with its high spatial resolution and global coverage, offers unprecedented opportunities for studying coastal environments. Although primarily designed for observing open ocean and inland water bodies, recent studies have demonstrated its ability to capture intertidal topography at low tide. One key challenge in such applications lies in separating intertidal pixels from water ones, as current SWOT classification lacks a dedicated intertidal class. This study introduces a standalone methodology that relies exclusively on SWOT level-2 High Resolution (HR) pixel cloud dataset. Intertidal pixels are identified using a simple approach based on the probability distribution function (PDF) of sea surface height anomalies relative to a nearby reference open water point. This method was applied to the macro-tidal, geographically complex coastal region of Pertuis Charentais along the French Atlantic coast. Validation against airborne LiDAR topography shows good agreement, with Root Mean Square Error (RMSE) below 30 cm for both single-cycle and temporally stacked SWOT observations. Performance was consistent across different bottom types, with highest accuracy over low slope (<1°) muddy and sandy bottoms and moderate degradation over rocky bottoms. Elevation profile analysis suggests that SWOT has a potential for detecting spatiotemporal morphological evolution in highly dynamic environments. While single-cycle observations are limited by inherent interferometric noise, annual stacks show promises in resolving long-term changes. These findings highlight SWOT's potential to fill key observational gaps in intertidal mapping, supporting coastal morphodynamic studies, hydrodynamic modeling and climate resilience efforts in data-sparse or rapidly evolving environments.