High-resolution characterization of intertidal areas and lowest astronomical tidal surface by use of Sentinel-2 multispectral imagery and hydrodynamic modeling: Case-study in Cadiz Bay (Spain)

In intertidal areas, the zonation is determined by factors such as sea-level and topography. For this reason, a mixed methodology for the characterization (topography, extension, and zonation) of maximum intertidal areas is presented, based upon multispectral satellite imagery, hydrodynamic modeling, and in situ measurements. The methodology is applied and validated in the inner Cadiz Bay (SW Spain) as a case study. Satellite-derived waterlines were vertically referenced by tide-gauge measurements of sea-level; the resulting partial topography of intertidal areas was integrated into available hydrographic/topographic data to elaborate a high-resolution (10 m) model grid from which hydrodynamic simulations were conducted. Model results for lowest and highest tidal level situations were used to characterize the maximum intertidal areas within the inner Cadiz Bay, as well as the lowest astronomical tidal surface (LAT). The obtained LAT, referenced with respect the chosen geoid and/or ellipsoid, was identified with the vertical reference surface for Hydrography (VRSH) in this environment, complementing and improving the official VRSH presently being developed for Spanish waters. Obtained results show errors of the order of 1 cm for sea-level amplitudes and <1 min for the main tidal lags when comparing with tide-gauge data. Further applications of this exportable, relatively fast, low-cost, and accurate methodology are outlined.