An evaluation of the problems of chlorophyll retrieval from ocean colour, for case 2 waters

Abstract

A reflectance model is presented that takes into account the spectral signatures of phytoplankton, dissolved organic matter and non-chlorophyllous particles. The model is validated by comparison with observed reflectance spectra. It is then used to simulate a data bank of reflectance spectra for a wide range of combinations of the three optically active substances in various concentrations. The in vivo chlorophyll-a fluorescence is masked. The simulated data are subjected to eigenvector and multiple regression analyses. It appears that the spectral signatures are sufficiently orthogonal to permit retrieval of the concentrations of individual components from the reflectance spectra. However, due to the non-linearity of the system, site-specific algorithms tailored to suit local conditions are likely to yield better results than a single universal algorithm for case 2 waters. Results indicate that the use of 400 nm in addition to the CZCS channels greatly enhances the capability to separate the phytoplankton signal from that of dissolved yellow organic matter. It appears possible to use 5 key-wavelengths (400, 440, 520, 565 and 640 nm) instead of the complete spectrum, without significant loss of information. The consequence of the variability in the backscattering signal of non-chlorophyllous particles is also examined.