Direct identification of absorption and scattering coefficients and phase function of a porous medium by a Monte Carlo technique

A general method of direct identification of absorption and scattering coefficients and phase function of porous media, assumed statistically homogeneous and isotropic, has been developed for wavelengths small in regard of the typical structure length (i.e. by neglecting diffraction). This method is here limited to a transparent fluid phase and an opaque solid phase. Diffuse and specular reflection laws and combination of these laws are considered. First results have been obtained for sets of Dispersed radius Overlapping Opaque Spheres (DOOS) in a transparent fluid phase, or sets of Dispersed radius Overlapping Transparent Spheres (DOTS) in an opaque solid phase. In the case of DOOS models, the absorption and scattering coefficients have the same analytical expressions as those characterizing the optically thin limit for any porous medium. For DOTS models, these coefficients have been, for porosity higher than 0.65, identified from Monte Carlo calculations versus the porosity or the specific area per unit volume of the fluid phase. For DOOS models, the phase functions have been expressed by a simple analytical expression in the case of a specular reflection law, and derived from Monte Carlo calculations in the case of the diffuse reflection law. For DOTS models, phase function have been numerically calculated from Monte Carlo calculations. The case of the combination of the two reflection laws is finally discussed.