Modifications to the surface albedo that result from surface melting may create a positive feedback on climate change, known as the "snow/ice - albedo feedback." Spectral albedo measurements of the Arctic surface have shown that individual features,such as melt ponds and leads, serve to substantially lower the albedo from typical values relative to pure ice. The albedo of a particular scene should thus be influenced by the fractional areal coverage of melt ponds and leads.
Aircraft observations of the Arctic surface have recently been obtained during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. A C-130 aircraft was equipped with a suite of instruments to view the surface during May and July 1998. A downward-looking video camera recorded continuously for the duration of each flight (16 total), which provided high (1.7m @ 1km altitude) resolution views of the surface during clear periods. Eppley pyranometers were mounted atop and on the underside of the aircraft and obtained hemispheric broadband downwelling and upwelling radiation, integrated from 0.285 to 2.80 micrometers.
A method has been devised to identify melt ponds within a video "snapshot," due to their unique spectral signature in the visible band. Melt ponds preferentially reflect blue over red, in contrast to the gray refelection exhibited by snow-covered and bare ice. Computer software utilizes this reflection difference to calculate the areal percentage of melt pond coverage within each "snapshot." Leads are also identified, due to their lower reflectance, when compared to the surrounding pack ice.
The variation of fractional melt pond and lead percentage should influence the albedo observed by the Eppley pyranometers. A relationship between melt pond / lead fraction and albedo will be proposed. Does the observed broadband albedo equal the sum of the individual feature albedos when weighted by their percentage area within the scene? How does the melt pond / lead fraction during SHEBA compare to previously observed and modeled values?