New Perspectives in the Monitoring of Marine Sedimentary Transport by Satellites—Advantage and Research Directions

Advances in satellite data, revisit times, computing capacity and processing speed are on their way to deliver a revolution in the monitoring and management of coastal erosion due to systematic remote sensing of the shoreline from space. This represents, and enables further, major progress on a far greater scale than the current state of the art. European public satellites of the Sentinel Constellation (Sentinel-1 and Sentinel-2) of the COPERNICUS program currently offer a revisit time of (i) five days with four satellites under the same viewing conditions, for bathy-topography investigation of the shoreline, i.e. from the continental shelf-break to the foreshore, (ii) a few days at mid latitudes but from different points of view, and (iii) almost daily at higher latitudes. The low resolution (5-to-20 m) of the radar & VNIR components of the time-series is mitigated by high spectral density that allows a true spectral analysis of the earth surface and waters, after appropriate corrections, i.e. removal of atmospheric scattering, sun glint and white caps effects, geometric configuration due to the anisotropic bidirectional soils & waters reflectance distribution function (BRDF). New tools in open source like the SNAP toolbox or interfaces like Coastal Thematic Exploitation platform allow public labs and companies to benefit from this breakthrough in data acquisition, rapid processing or database collection. Via remote sensing techniques, time series of seafloor bathymetry and suspended sediment in the water column can be derived from optical (spectral analysis) and SAR imagery (correlation between radar cross section changes and Bragg scattering of the water-foreshore surface for the assessment of the errors). It complements, when required, Very High Resolution (VHR) surveys made on order with commercial imagery, (or dug out from archives), aerial LiDaR (Light Detection and Ranging) with planes or drones, or depths sounders (on launches) and topographic instrumentation for beach profiling. Yet, the current swarms of nanosatellites such as Planet/Doves give access to systematic VHR cover of the earth. Such work can be carried out in the frame of national programs such as LITTO3D or regional/local programs.