Daly Christopher, Baba W., Bergsma E., Thoumyre Grégoire, Almar Rafaël, Garlan T. (2022). The new era of regional coastal bathymetry from space : a showcase for West Africa using optical Sentinel-2 imagery. Remote Sensing of Environment, 278, p. 113084 [14 p.]. ISSN 0034-4257.
Titre du document
The new era of regional coastal bathymetry from space : a showcase for West Africa using optical Sentinel-2 imagery
Daly Christopher, Baba W., Bergsma E., Thoumyre Grégoire, Almar Rafaël, Garlan T.
Source
Remote Sensing of Environment, 2022,
278, p. 113084 [14 p.] ISSN 0034-4257
Large-scale coastal bathymetry is paramount to understand natural and human-induced coastal behaviour and plays a vital role in coastal research and governance. Here, we use a recently developed algorithm, S2Shores (Satellite to Shores), to invert coastal bathymetry from wave kinematics, based on the linear dispersion relation. Wave numbers and celerity are extracted from optical Sentinel-2 imagery, by exploiting the small temporal offset between the image bands of its Multi-Spectral Instrument. Inverted depths are output at 200 m resolution, and individual depth points are merged to create a composite bathymetry using a weighted average of images from 10 different dates. The resulting bathymetry mosaic spans 4000 km along the West African coast. S2Shores is able to detect depths up to 35 m, depending on mean incident wave conditions and cloud cover, which varies by location. Underwater features are well reproduced by S2Shores, such as flow channels in Guinea, the St. Ann's Shoal in Sierra Leone, and ebb delta lobes at several outlets along the Niger River Delta. S2Shores results match well (r2 = 0.76, RMSE = 4.9 m) with a bathymetry survey along the Senegalese coast. As a difference with traditional satellite-derived bathymetry methods based on water colour, a wave-based approach allows estimations in turbid areas and relatively deep waters, which suggest that the two approaches are complementary and should be used in combination to cover coastal environments in their diversity. The new possibility offered by this regional coastal atlas opens the door to increased research and planning capabilities and sets an example that can be applied to the rest of the world.
