Optical Measurements of Sea Ice in the Gulf of Finland

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.