Polarimetric observations and theory of millimeter-wave backscatter from snow cover

Polarimetric radar measurements carried out at 95 and 225 GHz are presented for fresh and refrozen snow cover. These data indicate that the Mueller matrix for snow cover consisting of spherical ice particles has a relatively simple form, with 10 of the 16 elements approximately zero. Measurements of new-fallen snow consisting of predominantly nonspherical snow crystals are also presented. The anisotropic structure of such snow cover results in a more complex Mueller matrix, fitting the general form for natural surfaces. An analytic expression for the Mueller matrix of isotropic snow cover is derived by computing the response of a semi-infinite layer of scatterers that are insensitive to the orientation of the incident polarization. This matrix is shown to accurately predict the polarimetric response of the snow cover comprised of spherical ice particles based solely on copolarized and cross-polarized radar cross-section measurements