Retrieval of nearshore bathymetry from Sentinel-2A and 2B satellites in South Florida coastal waters Estuarine Coastal and Shelf Science

This study examines the relatively high-resolution MultiSpectral Instrument (MSI) onboard Sentinel-2A and 2B for generating bathymetric maps through a ratio transform model in South Florida (United States). Atmospheric correction of imagery is implemented though ACOLITE software, providing accurate performance and consistency over different Sentinel-2A/B scenes and three different study sites. Vertical calibration uses 5-10 points collected from digital charts, independent of lidar surveys, which are used for validation and error analysis. Satellite-Derived Bathymetry (SDB) has Median Absolute Error (MedAE) of 0.5 m in West Palm Beach (at depths ranging between 0 and 18 m, limit of lidar survey for validation), 0.4 m in Key West (0-5 m), and 0.22 m in Dry Tortugas (0-6 m), in conditions with low turbidity. Accurate bathymetry mapping can be accomplished with both sensors over environments with varying water transparency conditions, with the advantage of a fast, flexible, and economical solution. The 10-m MSI can capture small-scale features, such as tidal channels, straits relevant to navigation or steep slopes. While the least error is achieved by calibrating each image separately, a generic calibration produces only a moderately greater error with MedAE still similar to 1m, indicating the robustness of the approach. The research highlights the great potential of the 5-day revisit, suggesting that the twin Sentinel-2 mission of the Copernicus programme may enhance SDB to leverage its use for several operational purposes, particularly in remote and inaccessible regions of the world.