M96-1 for web

Sea ice is a translucent material with an intricate structure and complex optical properties. Understanding the reflection, absorption, and transmission of shortwave radiation by sea ice is important to a diverse array of scientific problems, including those in ice thermodynamics and polar climatology. Radiative transfer in sea ice is a combination of absorption and scattering. Differences in the magnitude of sea ice optical properties are due primarily to differences in scattering. Spectral variations are mainly a result of absorption. Changes in such optical properties as the albedo, reflectance, transmittance, and extinction coefficient are directly related to changes in the state and structure of the ice. Physical changes that enhance scattering, such as the formation of air bubbles due to brine drainage, result in larger albedos and extinction coefficients. The albedo is quite sensitive to the surface state. If the ice has a snow cover, albedos are large. In contrast, the presence of liquid water on a bare ice surface causes a decrease in albedo, which is more pronounced at longer wavelengths. Sea-ice optical properties depend on the volume of brine and air and on how the brine and air are distributed. For conversion of SI units to non-SI units of measurement consult ASTM Standard E380-93, Standard Practice for Use of the International System of Units, published by the American Society for Testing and Materials, 1916 Race St., Philadelphia, Pa. 19103. Cover: Dr. T.C. Grenfell measuring melt pond albedos on first-year ice near Barrow, Alaska. A Kipp radiometer, which measures total shortwave irradiance, is in the foreground. The cylindrical instrument on the tripod is a scanning spectroradiometer that measures spectral irradiance from 400 to 2500 nm.