Modelling the Backscattering Probability of Marine Particles in Case Ii Waters

In order to develop new methods to retrieve bio-geochemical or physical parameters of the marine environment from ocean colour data, either based on semi-analytic models or radiative transfer simulations, parameterisations of the inherent optical properties (IOPs) of the various constituents present in sea water are required. Such parameterisations are meanwhile rather well established for Case I waters [Bricaud et al., 1981; Bricaud et al., 1998; Loisel and Morel, 1998; Zhang et al., 2003]. The constituents present in Case II waters are characterised by a larger variability as compared to Case I waters. This variability as well as the difficulties encountered with in-situ determination of bio-optical parameters are the main reasons for the actual lack of bio-optical models for Case II waters. During the COASTLOOC (Coastal Surveillance Through Observation of Ocean Colour) project [Babin, 2000], bio-optical models of the absorption of nonchlorophyllous particles and coloured dissolved organic matter (CDOM) as well as marine particles scattering were developed from measurements taken in European coastal waters. One objective of this study is to develop a bio-optical model of the back scattering probability of marine particles which shall allow to simulate the light field in Case II waters with the accuracy required for the development of retrieval schemes for oceanic constituents. The model was derived by optimising the agreement between radiative transfer simulations of the hemispherical reflectance just below the sea surface and the corresponding COASTLOOC data.