Bidirectional anisotropic reflectance of snow and sea ice in AVHRR Channel 1 and 2 spectral regions. I. Theoretical analysis

The bidirectional reflectance anisotropy in Advanced Very High Resolution Radiometer (AVHRR) Channel 1 and 2 spectral regions for snow- and ice-covered surfaces was investigated using a comprehensive radiative transfer model for the coupled atmosphere, snow, ice, and ocean system. The model has been developed to include surface roughness effects. The importance of the scattering characteristics of snow and the surface roughness of sea ice to the bidirectional reflectance of these surfaces is presented. The modeled anisotropic factor, however, shows less sensitivity to aerosol loading and snow soot contamination than to solar elevation, snow phase function, and ice surface roughness. Results show high anisotropic reflectance factors (ARFs) and different reflectance features for snow and ice surfaces in both the AVHRR Channel 1 and 2 spectral regions. The model-observation comparison indicates that the model is able to predict the general characteristics of the bidirectional reflection of snow and sea ice. The introduction of surface roughness in the model can well explain the extremely strong forward or high anisotropic reflectance of sea ice.