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Laboratory determination of the characteristic reflection matrices of natural surfaces

A simple procedure to determine the elements of a 3×3 matrix which describes the reflection of light by natural surfaces composed of soil, sand, etc. is described. The procedure is based on the determination of the Stokes vector of the light reflected by the sample under different conditions of illumination, either with unpolarized or linearly polarized light. It is found that, in the principal plane defined by the direction of illumination and the normal to the mean surface, the reflection matrix is analogous in form to that of a specular reflector. The individual matrix elements are, however, suitably modified to account for the lack of complete polarization of the reflected light under all conditions of illumination.