Edward Salameh (Univ Rouen Normandie, Univ Caen Normandie, CNRS, M2C, UMR 6143, F-76000 Rouen, France , France); Erwin Bergsma (CNES, 18 Avenue Edouard Belin, CEDEX 9, 31401 Toulouse, France , France); Frédéric Frappart (ISPA, UMR 1391 INRAE/Bordeaux Science Agro, 33140 Villenave-D’Ornon, France, France); Ernesto Tonatiuh Mendoza (Univ Rouen Normandie, Univ Caen Normandie, CNRS, M2C, UMR 6143, F-76000 Rouen, France , France); Imen Turki (Univ Rouen Normandie, Univ Caen Normandie, CNRS, M2C, UMR 6143, F-76000 Rouen, France , France); Tatiana Goulas (Univ Rouen Normandie, Univ Caen Normandie, CNRS, M2C, UMR 6143, F-76000 Rouen, France , France); Julien Deloffre (Univ Rouen Normandie, Univ Caen Normandie, CNRS, M2C, UMR 6143, F-76000 Rouen, France , France); Sophie Le Bot (Univ Rouen Normandie, Univ Caen Normandie, CNRS, M2C, UMR 6143, F-76000 Rouen, France , France); Benoit Laignel (Univ Rouen Normandie, Univ Caen Normandie, CNRS, M2C, UMR 6143, F-76000 Rouen, France , France)

Intertidal flats act as a natural buffer between the sea and the land, protecting against coastal hazards such as storm surges. These dynamic environments are characterized by significant topographic variations driven by major processes and stressors, including tides, waves, freshwater inflow, storms, human activities, and climate change, all of which influence ongoing sediment redistribution. This emphasizes the growing need for accurate, up-to-date intertidal topographic maps. Spaceborne remote sensing is an efficient tool for monitoring these evolving landscapes and enables regular monitoring. As part of the SCO EO4Intertopo project, this study uses Sentinel-2, Sentinel-1 and SWOT observations to investigate changes in the intertidal topography of the Normandy coast over the past ten years. Sentinel-2 and Sentinel-1 DEMs were generated using a method that relates the inundation frequency of pixels to their corresponding elevations, while the SWOT_HR_PIXC product provides direct elevation measurements. Annual DEMs were generated from 2015 to 2024 using Sentinel-2, supplemented by Sentinel-1, and from 2024 to 2025 using SWOT. Comparing these with airborne LiDAR-derived DEMs at three specific sites (the Bay of Veys, Utah Beach and the Seine Estuary) showed mean absolute errors (MAE) ranging from 0.25 to 0.49 meters and root mean squared errors (RMSE) ranging from 0.41 to 0.70 meters. Validation was also performed using ICESat-2 laser altimetry observations covering the entire Normandy region. Correlation coefficients higher than 0.7 were obtained. Computing DEMs of difference (DoDs) has enabled the quantification of annual volumetric morpho-sedimentary changes (erosion, accretion and stable areas) at a regional scale along the Normandy coastline. Channel migrations and beach slopes were detected and analyzed in relation to hydrodynamic forcings and sedimentary characteristics linked to substrate types. These results demonstrate the potential of combining multi-source satellite observations, including SWOT, for long-term monitoring and understanding of intertidal morphodynamics in response to physical drivers.