In-situ observation of the microwave response of lead evolution

Numerous questions exist as to the air-sea-ice interaction processes which take place at leads in the Arctic. Leads are areas of open water or very new ice, and are generated in response to convergence-divergence in the polar pack. A critical proportion of the heat transfer and brine flux occurs in association with these features, especially during winter and spring. The Office of Naval Research (ONR) has sponsored a "lead processes study" in the Beaufort Sea via a manned ice camp. Leads are transient features. Newly formed leads were surveyed. In-situ radar scattering, physical property, oceanographic, and meteorological data were acquired. The focus of the paper is to describe the evolution of the microwave and physical properties as newly spawned lead age. A lead begins life as a region of open water, but a skim of ice forms rapidly when conditions become quiescent. Thicknesses of several centimeters are easily achieved within the first day. Formation of a rim type feature on the ice surface is observed once the ice exceeds just a few centimeters. A backscatter is observed in association with a bare ice sheet, 2-4 cm thick. Radar backscatter intensity in the microwave region (e.g. C-X-band) is found to increase with frost flower development. Thick first-year and multiyear ice signatures are also documented. These ice forms represent the "clutter" background from which the lead ice is to be detected. The final results and conclusions of the study are presented. The change in backscatter and physical properties are described as a function of ice thickness and growth interval.