Use of MODIS images to monitor water constituent concentrations in the Tuscany Sea

Paper Abstract Global standard ocean colour algorithms may be inefficient to estimate the concentration of seawater constituents in the Mediterranean Sea. Local overestimation or underestimation of chlorophyll, suspended sediments and yellow substance are in fact quite common. To avoid this problem, our research group works on the local calibration of empirical or semi-analytical algorithms through comparison to in situ measured data. The spectral features of chlorophyll, suspended sediments and yellow substance were found for a number of samples near the coast of Tuscany (Italy). An unconventional algorithm was then developed and applied to satellite data (MODIS) for the retrieval of water constituent concentrations. This inversion algorithm is based on the minimization of the spectral angle between simulated and measured remote sensing reflectances. The estimated concentrations show a lower error with respect to that obtained by a standard error minimization criterion. Monthly maps of seawater constituent concentrations obtained by applying the proposed algorithm to numerous satellite images confirm the oligotrophic nature of the Tuscany Sea, where high values of these concentrations can be found only in early spring near the mouths of the main rivers.