Optical Measurements of Sea Ice in the Gulf of Finland

Abstract

During the spring of 1998, measurements of total albedos, spectral albedos and ice transparency were made on coastal fast ice in the Gulf of Finland, Baltic Sea, to produce values for models, to compare instruments and to test a new method for measuring under ice irradiance. The broadband albedos between 400 and 700 nm varied between 0.19 and 0.76, and those between 300 and 1,100 nm were from 0.16 to 0.75. The condition of the surface, and especially the presence of liquid water or snow, was the most important factor affecting the albedos, but also the cloudcover and forest shading had an effect. The diffuse attenuation coefficient integrated over the range 400 to 700 nm was 6.8 m−1. Spectral albedos were weakly dependent on wavelength in the visible band (300-800 nm) decreasing in the longer wavelengths. The albedo results were in good agreement with earlier observations.

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

“…The shape of the spectral transmittance in the present study is close to what was obtained by Rasmus et al (2002): their maximum transmittance was 16% at about 550 nm, while our maximum transmittance was within 570-600 nm. Thus there is insignificant difference between reflectances of brackish landfast ice and lake-ice when they are covered by a similar snow cover.…”

“…For landfast sea ice (brackish ice) in the Gulf of Finland, broadband reflectances over the PAR band were 0.76 ± 0.1 for ice covered by dry snow, 0.38 ± 0.04 for dry bare rough ice, 0.30 ± 0.06 for dry bare smooth ice and 0.26 ± 0.07 for ice covered by a thin water layer (Rasmus et al 2002). The shape of the spectral transmittance in the present study is close to what was obtained by Rasmus et al (2002): their maximum transmittance was 16% at about 550 nm, while our maximum transmittance was within 570-600 nm.…”

Optical properties of melting landfast sea ice and underlying seawater in Santala Bay, Gulf of Finland

“…In Figures 7b–7d the model results are compared to K net and to K d determined from measurements of downwelling irradiance above and beneath the sea ice cover according to Here R s is the specular reflection from the ice surface; its value here is assumed to be 5% and depends on solar angle and the fractions of direct and diffuse irradiance [ Arrigo et al , 1991]. was used by, e.g., Arrigo et al [1991] and Rasmus et al [2002]. The results are shown in Table 2.…”

“…In the Baltic Sea, however, observations of the optical properties of sea ice and the underlying water column are sparse. A few spectral irradiance measurements in the Gulf of Finland were carried out by Blanco and Haapala [1995] and Rasmus et al [2002]. Leppäranta et al [2003] compared photosynthetically active radiation (PAR) measurements to the properties of seawater and melted ice samples.…”

Impact of UVA radiation on algae and bacteria in Baltic Sea ice

“…The fluctuating air temperatures result in meltingfreezing events in the Baltic Sea, exposing the ice to solar radiation and incorporating the melted snow into superimposed ice . Rasmus et al (2002) calculated that transmittance of UVA was from ca. 5 to 11% for 30 cm thick ice with 3 cm snow cover in Santala Bay, Gulf of Finland, in early April.…”