Author(s): Ants Erm; Juho Jakkila; Jari Uusikivi; Antti Kangas; Matti Lepparanta
Linked Author(s): Matti Leppäranta
Keywords: No keywords
Abstract: Spectral and integral optical properties of ice, ice meltwater and under ice water of some Estonian and Finnish lakes and of the Gulf of Finland were investigated as in the field and in the laboratory. In the field the albedo of ice and snow and irradiation above and under the ice were measured. The main purpose of this study was to answer the question: is it possible to learn about the optical properties of ice by investigating ice meltwater. In the laboratory the beam attenuation spectra of meltwater were measured, and concentrations of optically active substances (OAS) were analyzed. Although there are some irreversible processes going by freezing-melting cycles, especially in hard waters, the inherent optical characteristics of ice cover, including its vertical profile, could be estimated by studying of ice meltwater. The investigations have shown that not only the upper layer of ice (snow-ice) and bottom skeleton layer of sea ice may have an elevated amount of OAS, but there may occur optically denser layers inside the ice-sheet too, where the concentration of OAS could be some tens of g/m3 while the common level is below 5 g/m3. Assuming the optical density of distinctive layers is proportional to the amount of OAS, its values can be calculated. Two different approximations for the light field inside of ice were composed and compared: one based on the beam attenuation coefficient of meltwater and an other based on the concentration of the suspended matter. From these approximations more accurate transition coefficients to estimate the optical properties of the ice could be calculated, an specific attenuation coefficient of the suspended matter in ice also.
Year: 2008