Aurelien Carbonniere

Climate wave data, derived from significant wave height (SWH) altimetry, provide accurate information towards nearshore and coastal areas. Their use is crucial to enhance our capabilities of observing, understanding, and forecasting storm waves, even in complex coastal basins. In this study, SWOT nadir data were combined with nine existing altimeters for assessing waves and monitoring their evolution during storms in the English Channel, near UK–French coasts. Validation against wave buoys and numerical models shows high accuracy, with correlations around 95%, decreasing to 85% when buoy track offsets > 50 km, producing the largest errors. The multi-source approach enables depth-resolved monitoring, with SWH mapping revealing ~20–25% modulation in the Channel and ~36% dissipation near the Seine Bay during storms. Spectral analysis of multi-source altimeter-derived merged observations improve time-sampling, resolving high-frequency variability from monthly to daily scales and capturing ~75% of storms. Most storm wave features along altimetry tracks are resolved, with CFOSAT mapping nearshore areas and SWOT capturing coastal zones, both achieving ~80% variance. This temporal and spatial monitoring would be further enhanced with SWOT’s 2D wide swath. This finding provides a complementary, comprehensive understanding of coastal waves and offers valuable input for data assimilation, to improve storm wave estimates in coastal basins.

Nowadays, most satellite altimeters have proven effective in providing datasets on sea surface changes in oceans towards nearshore zones. The need to extend satellite sea level and wave records closer to the coast has been a focus of several studies investigating the accuracy of observations in shallow water areas and coastal zones, with the aim of monitoring spatial and temporal changes in the hydrodynamics. The recently launched Surface Water and Ocean Topography (SWOT), is the first wide-swath interferometric altimetry mission. Here, we integrate SWOT observations with 9 existing altimeters for assessing the Significant Wave Height (SWH) at regional and local scales with a special focus on high energetic periods. The monitoring of storms using multisource altimeters offer the possibility to enhance their evolution with full coverages. The combination of SWOT with conventional altimeters improves the time-sampling to capture the variability modes from inter-monthly to inter-daily scales, including storms; and the spatial sampling that would be expanded thanks to the SWOT 2D consistent view. The frequency analysis of SWH along tracks highlights the wavelength of wave features and their changes during storms. This challenging issue benefits from ongoing works of new altimeters, including SWOT, to offer reliable estimates of coastal waves.