OBSERVATIONS OF THE POLARIZATION OF LIGHT REFLECTED FROM SEA-ICE

As part of a large, interdisciplinary program investigating the electr omagnetic properties of sea ice, we made spectral measurements of the albedo, reflectance, and Stokes vector of the reflected radiance field . The overall program encompassed observations of sea ice physical pro perties, optical properties and microwave properties, plus an extensiv e modeling effort. Measurements were made of an evolution sequence inc luding young sea ice, pancake ice, snow-covered ice, first-year ice, a nd ponded ice. The effects of surface roughness were investigated by a rtificially roughening part of a 31-cm-thick, smooth, young ice sheet. Spectral and total albedos were sensitive to surface conditions, cons istent with earlier studies. Stokes vector observations exhibited the greatest variability in the plane of incidence of the solar beam. Refl ectances at 0 degrees azimuth increased sharply with zenith angle. Smo other surfaces, such as melt ponds, pancakes and bare ice, exhibited a larger increase than the snow-covered cases with their ''rougher'' su rfaces. Since the solar zenith angle was close to Brewster's angle, sp ecularly reflected light was highly polarized. In the ''smooth'' ice c ases, there was significant polarization associated with the increase in reflectance, implying a substantial contribution from specular refl ection. This contribution was greater at longer wavelengths, where spe cular reflection was a larger component of the reflected radiance. Awa y from the plane of incidence, the Stokes vector showed little angular variation, and the reflected light at these angles was largely unpola rized.