Sea ice microstructural characteristics in the Barents Sea in autumn: relevance to microwave remote sensing

The microstructural characteristics of sea ice during autumn freeze-up in the Barents Sea were measured during a microwave remote sensing validation campaign aboard the US Coast Guard icebreaker Healy during October-November 2001. Ice samples were obtained from 16 ice floes and digital images of the thin and thick sections were taken to examine the characteristics of the brine and void structure. Due to the dynamic nature of the marginal ice zone, brine structure in first-year or thin ice was highly variable. Although brine pockets were typically elongated and tube-like, they could either be randomly oriented or aligned vertically, and may form either well-connected network or relatively isolated pockets. Some samples contained a significant fraction of air bubbles. Multi-year ice was typically very porous. Void diameters ranged from less than 0.1 mm to several centimeters and were often nonspherical. Of particular importance for microwave scattering, the larger voids may have contained either brine or air, depending on the fluid permeability of individual cores. A wide range of void fractions were observed in the upper, salt-free layers of the ice, which could account in part for the range of backscatter values observed for multi-year ice.