Improved detection of turbid waters from ocean color sensors information

Various empirical techniques have been developed to identify turbid marine waters within satellite ocean color imageries. The present technique, which essentially rests on the enhancement of reflectance in the green part of the spectrum when sediments are present, accounts for the improved knowledge regarding the relationship between the chlorophyll concentration and the scattering coefficient in oceanic case-1 waters. It also accounts for the bidirectional character of the light field emerging from a water body and thus for the sensitivity of the water-leaving radiance to the observational conditions (viewing angle and sun angle). Therefore, the thresholds, above which the turbid waters can be detected, are not constant. They depend on the chlorophyll concentration and on geometry (on the zenith-sun angle). The practical way of implementing such a discriminating tool is explained. Examples of the application of this technique are provided for level-2 and level-3 satellite data (SeaWiFS and MERIS).