Optical properties of the water in a deltaic environment: Prospective tool to analyze satellite data in turbid waters

In vivo absorption spectra, pigment concentrations from algal cultures, and field samples (Po Delta, Northern Italy) are analyzed to differentiate the contribution by each optically active constituent to the total absorption by the water. The results yield systematic trends in the blue:red and blue:NIR absorption ratio for living phytoplankton cells and detrital material, which are then used to retrieve the absorption coefficient of dissolved organic material (yellow substance) at 410 nm from the total in vivo absorption coefficients of natural waters at 410 nm, 670 nm, and 730 nm. A simple model has then been applied to retrieve in situ absorption coefficient by yellow substance and for different values of blue:red/NIR absorption ratios. Sensitivity and regional tests in the studied site and in the Baltic shows that the model can explain more than 85% of the variance in the observed data under various conditions of turbidity, and shows that predicted yellow substance is more sensitive to a change in detrital material than a change in living phytoplankton. Such work can be used with remote sensing techniques to differentiate the optically active constituents in coastal and turbid waters. Suggestions are given to solve the problem related to the backscattering coefficient of the water, and to propose an accurate method to remove the atmospheric effect from the remotely sensed signal.