LIGHT-REFLECTION FROM SEA-ICE DURING THE ONSET OF MELT

A knowledge of the reflection of light from a sea ice cover is important for the interpretation of remote sensing imagery at visible and near-infrared wavelengths, for climatological studies involving the energy balance of the polar regions, and for understanding radiative transfer in sea ice. Spectral measurements of albedo, bidirectional reflectance distribution function, and polarized reflectance were made for Arctic sea ice conditions found during the onset of melt. The wavelength region studied was from the visible to the near infrared (400-1000 nm). Results are presented for the five following surface types: (1) dry snow, (2) dry snow with a glazed surface, (3) bare ice, (4) blue ice, and (5) melt pond. Results indicate that spectral albedos decrease at all wavelengths as the melt season progresses and the surface conditions evolve from (1) through (5) and that the decrease is most pronounced at longer wavelengths. Reflectance data suggest that at most angles, reflectance has the same spectral shape as albedo; at 30-degrees zenith, reflectance is for the most part azimuthally isotropic; and at 60-degrees zenith there is a significant specular component at 0-degrees azimuth, especially for the bare ice cases. Light reflected at 60-degrees zenith angle was strongly polarized. In general, light reflected from snow-free ice was more strongly polarized, with the degree of polarization increasing with wavelength.