Bathymetry of the Golfe d’Arguin, Mauritania, derived with the moderate resolution Sentinel-2 satellites

We derive bathymetry with the Sentinel-2 medium-resolution (20m) satellites, using the shallow depth wave dispersion relationship. Our test area is the Golfe d’Arguin, Mauritania, a shallow shelf extending 120 km from shore. A semi-enclosing shoal (the Arguin Shoal) divides the area into a very shallow inner basin and an outer shelf. The ground truth for validation is a 1962 French Hydrographic Survey in the area of the infamous 1816 Medusa stranding on the Arguin Shoal. Our bathymetry accurately located the edge of the shoal (8m isobath) and mapped the outer shelf to 35 m depth. The Sentinel-2 maps the bathymetry with 200 m resolution, significantly better than the (at best) 2 km resolution of International Hydrographic organization charts (commonly known as GEBCO). Of particular note (and relevance to navigation safety), we found an uncharted 6-8m deep reef in the outer shelf with mounds rising from the reef floor to 2-3m depth. Based on the Golfe d’Arguin results, we conclude that Sentinel-2 satellites may be applied in other coastal areas with suitable waves and sun illumination. The optimum conditions are long wavelengths (peak wavelength $\geq$100 m) waves, and sun zenith angles 20°-40°. The most promising are coasts in tropics and mid-latitudes exposed to Atlantic, Pacific, or Indian oceans storm waves.