Complex yet translucent: The optical properties of sea ice

Don Perovich

USACE Engineer Research and Development Center
Cold Regions Research and Engineering Laboratory
72 Lyme Road, Hanover,
New Hampshire, 03755-1290 USA

Sea ice is a naturally occurring material with an intricate and highly variable structure consisting of ice platelets, brine pockets, air bubbles, and precipitated salt crystals. The optical properties of sea ice are directly dependent on this ice structure. Since sea ice is a material that exists at its salinity determined freezing point, its structure, and optical properties, are significantly impacted by small changes in temperature. Understanding the interaction of sunlight with sea ice is important to a diverse array of scientific problems, including those in polar climatology. A key optical parameter for climatological studies is the albedo, the fraction of the incident sunlight that is reflected. The albedo of sea ice is quite sensitive to surface conditions. A presence of a snow covered enhances the albedo, while surface meltwater reduces the albedo. 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, while spectral variations are mainly a result of absorption. Physical changes that enhance scattering, such as the formation of air bubbles due to brine drainage, result in more light reflected and less transmitted.