Field investigations of apparent optical properties of ice cover in Finnish and Estonian lakes in winter 2009

Abstract

A field programme on light conditions in ice-covered lakes and optical properties of lake ice was performed in seven lakes of Finland and Estonia in February–April 2009. On the basis of irradiance measurements above and below ice, spectral reflectance and transmittance were determined for the ice sheet; time evolution of photosynthetically active radiation (PAR) transmittance was examined from irradiance recordings at several levels inside the ice sheet. Snow cover was the dominant factor for transmission of PAR into the lake water body. Reflectance was 0.74–0.92 in winter, going down to 0.18–0.22 in the melting season. The bulk attenuation coefficient of dry snow was 14–25 m–1; the level decreased as the spring was coming. The reflectance and bulk attenuation coefficient of snow-free ice were 0.1–0.4 and 1–5 m–1. Both were considerably smaller than those of snow cover. Seasonal evolution of light transmission was mainly due to snow melting. Snow and ice cover not only depress the PAR level in a lake but also influence the spectral and directional distribution of light

Numerical modelling of snow and ice thicknesses in Lake Vanajavesi, Finland

“…On 14 April, a 3-cm slush layer was still observed but snowÁice had disappeared. The melt rate of ice was 1 cm d (1 from 7 April to 14 April (Lei et al, 2011), both in the model and in the observations. The melting of ice started in the beginning of April, as soon as snow had gone, and it accelerated towards the breakup (Fig.…”

“…This error is likely due to overestimation of snow density in the model. Later, on 7 April, a 2-cm slush layer and a 5-cm frozen slush layer were observed (Lei et al, 2011), while in NUMERICAL MODELLING OF SNOW AND ICE THICKNESSESour simulation these values had become 2.9 and 2.7 cm, respectively, by the end of March. On 14 April, a 3-cm slush layer was still observed but snowÁice had disappeared.…”

“…Hydrographical surveys were made regularly, an automatic ice station was set up and optical investigations were performed (Jaatinen et al, 2010;Lei et al, 2011). The average maximum snow and ice thicknesses reached 15 and 41 cm, respectively, in March.…”

“…Snow to snowÁice transformation also contributed a little to the total ice thickness in the late season. A 9-cm slush layer and a 1-cm snowÁice layer were measured on 18 March (Lei et al, 2011), while the model prediction was a 5-cm slush layer and no snowÁice. This error is likely due to overestimation of snow density in the model.…”

Winter conditions in six European shallow lakes: a comparative synopsis

“…Scalar irradiance is therefore higher than PAR measured conventionally by planar sensors. Moreover, the spectral distribution is also different (Dokulil, 1979;Lei et al, 2011). The concentrations of suspended matter and chlorophyll a as well as the beam attenuation coefficient under the ice are markedly lower than the maxima during the ice-free period.…”