An algorithm for the retrieval of sediment content in turbid coastal waters from CZCS data

Abstract

An algorithm for the retrieval of the sediment content of turbid coastal waters from Coastal Zone Colour Scanner (CZCS) data has been developed theoretically and tested against experimental values. The theoretical approach consisted of numerical simulations and sensitivity analyses, focused on the search for a retrieval variable with low sensitivity to chlorophyll-like pigments, and to uncertainties in the procedure for the determination of the atmospheric correction applied to the remotely measured radiances. The variableX, = [R(550) - R(670)]° [R{520)/R(550)]6where R(λ) is the subsurface irradiance reflectance at wavelength X, has been found to meet the above requirements, provided 0–5asλ 1·5 and – 2·5≤b≤–0·7. The algorithm log(sed.) = A + Blog(Ars) has been applied to the analysis of a set of CZCS scenes of the Adriatic Sea, with sediment and chlorophyll concentration ranges from 1 to 13gm-3 and from 0–1 to l–5mgm~3, respectively. The theoretically predicted low sensitivity to the atmospheric correction method has been confirmed by the experimental evidence, suggesting the possibility of using a simplified correction procedure, even in turbid waters where sediment and chlorophyll contents are uncorrelated. The experimental exercise led to the identification of two water types in the northern basin of the Adriatic Sea, characterized by a substantially different correlation between sediment and chlorophyll, and corresponding to coastal zones with different hydrological conditions