The elements of the Mueller matrix for polydisperse systems of irregular, randomly oriented particles have been measured in absolute terms as a function of scattering angle for two wavelengths. These results have been compared to the matrix elements that were calculated for assemblies of spherical particles that fit the same particle size distribution function and have the same (real) refractive index.
A. C. Holland and G. Gagne, "The Scattering of Polarized Light by Polydisperse Systems of Irregular Particles," Appl. Opt. 9, 1113-1121 (1970)