Bidirectional Reflectance of Polar and Alpine Snow Surfaces

The reflectance distribution of polar and alpine snow was measured under various conditions at 450, 514, 750 and 1000 nm wavelength. A reflectance peak appears in the azimuth directions up to 60° to both sides of the solar azimuth, is more prominent at high zenith angles of incidence and of reflectance and is better developed in coarse than in fine-grained snow. Under natural conditions, when only hemispherical-directional reflectivity can be determined, the anisotropy is spread in the blue part of the spectrum where the diffuse component dominates global irradiance. Bidirectional reflectance of a laser beam at 514 nm over alpine snow is comparable to that at 1000 nm over polar snow.