Microwave study of the formation of brine layers on homogeneous saline ice sheets

When sea water freezes into sea ice, brine and pure ice are produced. Due to the effects of the expulsion of brine from the sea ice interior and the wicking action of snow and frost flowers deposited on the air-ice interface, brine may accumulate on the upper ice sheet surface. Brine is a concentrated solution of sea salts and water, hence is highly lossy and has a large dielectric constant. Sea ice which is several hours old transforms to a layer which, as a bulk dielectric constant, is considerably less than that of the sea water from which it was born. Questions arise as to the impact of the surface brine layer. Potentially, the air-ice interface the reflectivity and transmission characteristics of this upper most ice layer may be perturbed. The purpose of this work is to quantify the importance of a brine layer on an ice surface, the type of changes in the microwave signature which may occur, and the expected signal dynamics. Predicted results are produced by the integration of an n-layer reflectivity model for use in determining the effective reflectivity of the air-brine-ice-water system, a sea-ice electrical-property model for predicting the ice sheet permittivity profile based on the temperature and salinity profile, an electrical-property model for brine, and EM models based on Kirchoff methods to predict backscatter for a rough surface. These results are compared with in-situ observations conducted during the recent Office of Naval Research Accelerated Research Initiative of the Electromagnetics of Sea Ice. Model predictions and measured data extend the microwave and millimeter-wave (0.5 to 95 GHz) portion of the electromagnetic spectrum