Electrical, Optical and Acoustical Properties of Snow. Report of Committee Meeting,
EIDGENOESSICHES INST FUER SCHNEE- UND LAWINENFORSCHUNG DAVOS (SWITZERLAND)
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Measurements and modeling of the complex dielectric constant of dry and wet snow in the frequency range up to 100 MHz allow accurate 1 accuracy determinations of the snow wetness in the range of 0.5 to 30 water content as well as particle shape and possible surface parameters. Ground based active radar systems are in use for snow profiling and water-equivalent determinations. Radar radiometers and active radar systems ground-, aircraft - and satellite-based show improved performance for snow water-equivalent, wetness, melt-freeze cycle determinations and snow cover mapping. More work is needed to include and correct for the stratification of the snow cover and the structure of the snow. The most important model parameter is the correlation length distribution which can be directly determined from thin sections. Radar measurements are also used for avalanche speed measurements. Visible and near-infrared measurements of albedo are generally well-explained by model calculations, but further observations and modeling efforts are needed. The most important snow parameter is optical grain size a second important parameter is impurity content. The influence of snow surface structure on the albedo is less than the influence of these other two parameters, but may be important for very low sun angles. Thermal emissivity of snow is about 99, essentially independent of snowpack parameters.