Investigations of newly formed sea ice in the Cape Bathurst polynya: 2. Microwave emission

This study examines the role of newly formed sea ice geophysical state on microwave emission. Coincident with sea ice geophysical sampling, ship-based passive microwave emission data (dual-polarized at 19, 37 and 85 GHz) were collected in the Cape Bathurst Polynya during 18 October and 13 November 2003. Using polarization ratios (PRs), we found that bare thin ice was separable from snow-covered ice. Thin snow (equal to 0.02-0.13 m) thickness is significantly correlated with the spectral gradient ratios GRV(85,19) (R2 = 0.55, P-value <0.05) and GRV(85,37) (R2 = 0.66, P-value < 0.05), but not with GRV(37,19) (R2 = 0.19, P-value > 0.2). The relationship between atmospherically corrected R37 and bare ice thickness showed an exponential relationship very comparable to that reported by Martin et al. [2004], which is ascribed to the reduction of bare ice surface salinity based on both observational and modeling studies. However, the relationship quickly becomes invalid for even thin snow covered ice, due to significant impact of thin wet (liquid water fraction ∼0.02-0.04) snow on microwave emission. Our results suggest that the sea ice algorithms NASA Team and NASA Team 2 could underestimate total ice concentration over thin bare ice by 35% on average, while both algorithms underestimate the total ice concentration by 20% over snow-covered ice. Using PR(85) sea ice could be delineated from open water using a properly adjusted threshold value accounting for cloud or fog effects, possibly with the exception of dark nilas and/or bare consolidated pancakes.