Author(s): Ants Erm; Ove Parn; Fred Buschmann
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Abstract: Apparent optical properties of ice in the largest lakes of Estonia Lake Peipsi (3555 km2) and Lake Vortsjarv (270 km2) are discussed. Photosynthetically active radiation (PAR) was measured above as well as under the ice cover, also the restriction coefficient r (λ) of ice and snow were registered for every series of measurements. From the measured field data attenuation coefficients were calculated separately for the snow, ice and under ice water. These coefficients varied in great ranges (10–20 m-1 for the snow, 1–6 m-1 for the ice and water) depending on the ice and snow structure and existing of suspended matter in these. Maximum thickness of ice in ivestigated lakes normally was between 40–70 centimeters, the transparency depended more on the snow thickness than on the optical density of ice. Although there are some irreversible processes going by freezing-melting cycles, the inherent optical characteristics of ice cover, including its vertical profile, can be estimated by studying of ice melt-water. Beam attenuation spectra and suspended matter concentrations of melt-water of ice layers (of the snow and congelation ice in the most cases) were measured in the laboratory. Collected data showed that the congelation ice was much more pure than the overlying sheets of the snow ice and snow (attenuation rates about ~1 m-1, ~5 m-1 and 5–10 m-1 accordingly).
Year: 2012