Abstract
Climatological changes occur globally but have local impacts. Increased storminess, sea level rise and more powerful waves are expected to batter the coastal zone more often and more intense. To understand climate change impacts, regional bathymetry information is paramount. A major issue is that the bathymetries are often non-existent or if they do exist, outdated. This sparsity can be overcome by space-borne satellite techniques to derive bathymetry. Sentinel-2 optical imagery is collected continuously and has a revisit-time around a few days depending on the orbital-position around the world. In this work, Sentinel-2 imagery derived wave patterns are extracted using a localized radon transform. A discrete fast-Fourier (DFT) procedure per direction in Radon space (sinogram) is then applied to derive wave spectra. Sentinel-2 time-lag between detector bands is employed to compute the spectral wave-phase shift and depth using the gravity wave linear dispersion. With this novel technique, regional bathymetries are derived at the test-site of Capbreton, France with an root mean squared (RMS)-error of 2.58 m and a correlation coefficient of 0.82 when compared to the survey for depths until 30 m. With the proposed method, the 10 m Sentinel-2 resolution is sufficient to adequately estimate bathymetries for a wave period of 6.5 s or greater. For shorter periods, the pixel resolution does not allow to detect a stable celerity. In addition to the wave-signature enhancement, the capability of the Radon Transform to augment Sentinel-2 20 m resolution imagery to 10 m is demonstrated, increasing the number of suitable bands for the depth inversion.
Highlights
Climatological extremes are occurring more frequently and with greater intensity, in particular, coastal flooding and higher intensity storms [1,2]
The results show that wave patterns can be extracted by a local application of the Radon transform [20] (RT) for two different wave conditions and depth can be estimated
Wave patterns are extracted by applying an RT and subsequent angle filtering to Sentinel-2 imagery so that the wave signal contains the most-dominant wave directions
Summary
Climatological extremes are occurring more frequently and with greater intensity, in particular, coastal flooding and higher intensity storms [1,2]. These environmental changes and associated risks are often described in terms of sea level at the coast. Sea level at the coast can be broken down into several contributors such as regional sea level and wave contribution. The latter is dictated by the underlying bathymetry. As a matter of concept, powerful conditions such as storms can be considered large sediment transport drivers in the near-shore. Considering the dynamic coastal bathymetry to better predict its action on waves is paramount
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