Diffuse and coherent backscattering of polarized light: Polarization ratios for a discrete random medium composed of nonspherical particles

For a sparse, disordered, plane-parallel particulate medium, we analyze quantitatively the effects of particle microphysical properties on the values of the linear and circular backscattering polarization ratios. Using numerically exact T-matrix and vector radiative-transfer codes, we performed computations for the following models: (1) a semi-infinite homogeneous layer composed of randomly oriented, polydisperse oblate spheroids with the real part of the refractive index equal to 1.2, 1.4 and 1.6 and the imaginary part of the refractive index equal to 0 and 0.01; (2) a semi-infinite homogeneous layer composed of randomly oriented, polydisperse, oblate circular cylinders with the refractive index 1.4; (3) finite homogeneous layers of various optical thickness composed of randomly oriented, polydisperse, oblate spheroids with the refractive index 1.55. Our computations demonstrate that the values of the polarization ratios depend substantially on particle shape, real and imaginary parts of the particle refractive index, particle size relative to the wavelength, illumination geometry and optical thickness.