Inversion of Reflectance Spectra of Nonchlorophyllous Turbid Coastal Waters

This article deals with the inversion of reflectance spectra measured in the Rhône River mouth area during a flood event in terms of parameters characterizing the turbid water components. The optically active constituents considered are the total suspended matter, mainly composed of sediment, of known concentration ranging from 3.7 mg L−1 to 234 mg L−1, and yellow substance. A simple reflectance model is presented. Scattering is treated by Mie theory applied to a collection of particles of real refractive index mp and obeying a Junge size distribution law. A sensitivity study performed on the model shows that both concentration and refractive index and both cutoff particle diameters of the Junge size distribution law cannot be accurately determined from a given reflectance spectrum. Two model parameters, among a total of six, are estimated from model inversion: mp and a parameter characterizing the yellow substance absorption spectrum, ay0=ay (440 nm). The derived values are realistic as compared to the values that can be found in literature. Other combinations of parameters could be determined by inversion but measurement of mp and ay0 from reflectance spectra already has interesting applications in a satellite remote sensing perspective. Increasing the number of parameters of the model is feasable, but much work is needed to envisage the inverse problem.