Ground measurements of the polarized bidirectional reflectance of snow in the near-infrared spectral domain: Comparisons with model results

Ground-based measurements were carried out in the French Alps in March 1995 to study the bidirectional and polarized bidirectional reflectances of various snow covers. Atmospheric (optical thickness) and snow characteristics (grain size and type) were measured simultaneously. The ground reflectance data are compared with snow reflectance modeling results. A radiative transfer model based on the adding-doubling method is used to compute the snow reflectance. The single-scattering parameters are determined by a Mie or a ray-tracing code depending on the particle shape introduced in the model (spherical or hexagonal ice particles). Special attention is paid to the comparisons in the near-infrared spectral range (1.65 mu m) because of the sensitivity of snow reflectance to the grain size and shape. In the visible and near-infrared domains of the solar spectrum, the amplitude of the polarized signal is very low and independent of the snow grain size. The agreement between measurements and model results is good if hexagonal particles are introduced in the model instead of the spherical snow grains commonly used in reflectance studies.