Studying the factor of ice of icing field loss from fresh water in the millimeter range

In this work, the attenuation of microwave radiation in an artificially formed icing field on the ice cover of a freshwater lake was measured in the millimeter range. The measurements were made using microwave radiometry at frequencies of 22, 34, 90, and 125 GHz with a cyclic change in the ambient temperature in the range from -19 to -31 °C. A special technique was used, which makes it possible to determine the attenuation of microwave radiation in it from the increments of radio brightness temperature between ice cover and without icing field. In the proposed method, the loss factor was found under the condition that attenuation in ice is determined by electromagnetic losses in the medium. The measurements were carried out on the ice cover of a fresh lake with a water salinity of about 100 mg/l. As a result of the study, it was found that the formation of radiation by ice is strongly influenced by scattering on inhomogeneities of the medium. This conclusion was made from a comparison of the calculations of the expected ice loss factor of icing field and the data obtained from measurements by the method used. The greatest difference in the loss factor (several tens of times) was found at frequencies of 90 and 125 GHz. It has been suggested that radiation scattering occurs on crystalline hydrates of salts and can be caused by increased electrical conductivity of thin water films on the surface of crystals. This feature can arise, as was recently established, during the formation of ice 0 crystals in the medium. This ice is formed from deeply supercooled water at temperatures below -23 °C. The observed effect is of interest for the development of radar measurements of fresh natural ice at low temperatures and low concentrations in salts (about 100 mg/kg). Such ice can form from slightly salty water with a salt content of up to several grams per liter or when water with a salinity of ~ 100 mg/l freezes in a confined space. The results obtained are of interest for microwave aerospace determination of areas of the ice cover with its structural disturbances, through which the water of the reservoir can penetrate to the ice surface with subsequent freezing. At the same time, radars can be effective at icing field temperatures below -20 °C, when liquid inclusions almost completely freeze out. For the temperature range above the eutectic point, where liquid inclusions appear, passive radiometric measurements can be effective.