Remote sensing and coastal morphodynamic modelling: A review of current approaches and future perspectives

We want to investigate the use of remotely sensed data in shoreline morphodynamic modelling. For this aim, we present a review of current approaches for Total Suspended Matter (TSM) retrieval from satellite data in coastal waters and outline some perspectives for the definition of an operative, satellite-based, alongshore sediment flux. Coastal, turbid and optically complex waters have traditionally posed challenges to remote sensing and space-borne techniques for a variety of reasons: the complexity and variability of their radiative processes on one hand; spatial, temporal and spectral resolution issues on the other. Nevertheless, different sensors/satellites have been used in order to retrieve the main biogeochemical characteristics of these waters. Geostationary satellites (such as SEVIRI for European seas and COMS1 for South Korea) have been recently adopted for their high temporal resolution while classical ocean colour mappers (such as SeaWiFS, MODIS, MERIS, VIIRS) and other Earth observation satellites (like the Landsat series, Envisat, ERS series and Sentinel program) are commonly used because of their finer spatial and spectral resolutions. The immediate future looks promising because of the recent launch of the first satellite of the Sentinel-3 constellation with a new ocean colour instrument (OLCI) (21 spectral bands, 300m spatial resolution and a revisit time of 1.4 days). In the longer term, from 2018 onwards, the launch of Hyper Spectral instruments (e.g., German EnMAP, Italian PRISMA) with much higher spectral resolution capabilities, although at the expenses of a lower time resolution, promises finer water constituents determination and grain size characteristics, based on their spectral signatures. Consequently, a large variety of different methods, empirical or semi-analytical, are used by the scientific community in order to get the most suitable algorithm for the TSM retrieval. Envisaged developments include multi sensor approaches, new algorithms, coupled sea-atmosphere radiative transfer models. We here discuss the best strategy in order to achieve the most suitable regional TSM product for coastal geomorphologic applications and thus to pair it with coastal water velocity fields, allowing for a satellite-based definition of alongshore sediment transport.We also discuss spatial, temporal, and spectral characteristics of different sensors and novel algorithms that might combine these properties together.