Results of a stratified snow emissivity model based on the wave approach: Application to the Antarctic ice sheet

The results from a snow emissivity model are used to help with the interpretation of the Scanning Multichannel Microwave Radiometer data (aboard the satellite Nimbus 7, 1978–1986) over Antarctica. The model is based on the solution of Maxwell's equations through strong fluctuation theory (Stogryn, 1986). The snow is considered isothermal with horizontal stratification, isotropic inside each stratum, and with smooth interfaces. To wipe out the interference pattern created by plane stratification and in order to take into account the spatial variability of the snow characteristics, the final result is a mean value of many computations done with many stratigraphies randomly distributed around a mean profile. The spatial distribution of the microwave signatures over Antarctica reveals three areas with typical spectral signatures. These areas are identified from the point of view of snow characteristics through a ground data set (Surdyk and FiIy, 1993). The model reproduces well the effect of the stratification on the polarization differences as observed. The strong gradient of emissivity versus frequency observed on one of the test sites is not completely understood. Depth hoar layers characterized by faceted and cup‐shaped, coarse snow grains seem to have a particular scattering behavior compared with that of the usual grains. When those coarse grains are replaced by fine grains, the model results are closer to the measured data. The presence of crusts, the roughness at the snow‐ice interfaces, and crystal orientation may also have significant effects.