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 reflectan ces of various snow covers. Atmospheric (optical thickness) and snow c haracteristics (grain size and type) were measured simultaneously. The ground reflectance data are compared with snow reflectance modeling r esults. A radiative transfer model based on the adding-doubling method is used to compute the snow reflectance. The single-scattering parame ters are determined by a Mie or a ray-tracing code depending on the pa rticle shape introduced in the model (spherical or hexagonal ice parti cles). Special attention is paid to the comparisons in the near-infrar ed spectral range (1.65 mu m) because of the sensitivity of snow refle ctance to the grain size and shape. In the visible and near-infrared d omains of the solar spectrum, the amplitude of the polarized signal is very low and independent of the snow grain size. The agreement betwee n measurements and model results is good if hexagonal particles are in troduced in the model instead of the spherical snow grains commonly us ed in reflectance studies.