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Coupled forward and inverse radiative transfer modelling.  Sanjuan Calzado, Violeta; Fournier, Georges. CMRE-FR-2014-027. December 2014.

The optical signature in the ocean is a result of the absorption and scattering processes in the medium with particles. Calculating the radiant field from these absorption and scattering interactions is a well known problem. The radiant distribution is calculated from the radiative transfer equation, where state of the art models are able to reproduce similar boundary conditions as in the environment. The inverse problem, where the absorption and scattering processes are calculated given a radiant distribution, has only been attempted once with numerical formulations. Gordon's algorithm is discussed here and evaluated for success under a variety of different types of scenarios. The algorithm convergence in shallow water scenarios with high bottom reflectivity and sediment resuspension is moderate with average convergence of 50%, whereas in oceanic stations it is less than 5%, even in scenarios presenting vertical stratification. However, the calculation time is very high and therefore it is notappropriate for implementation in any operational system. Based on Gordon's formulation, a new inversion algorithm has been developed, with excellent results compared with Gordon's approach. The algorithm does not include a forward radiative transfer model; therefore the computational time required is minimal. Initial tests have shown excellent agreement when introduced in an iterative fashion with a forward radiative transfer model compared with measured absorption and backscattering data.