Sea ice surface features in Arctic summer 2008: Aerial observations

Eight helicopter flights were conducted, and more than 9000 aerial images were obtained during the Third Chinese National Arctic Research Expedition in 2008 in the Pacific Arctic Sector (PAS). Along the cruise tracks between 77°N and 86°N, area fractions of open water and ice cover varied from 0.96 to 0.12 and from 0.03 to 0.81, respectively, while the melt pond fraction varied between 0 and 0.2. The ice concentrations derived from aerial images and the AMSR-E/ASI products were comparable to each other, especially in the range of 50–90%. However, the satellite-derived data overestimated the aerial observations by 14 ± 9% in areas with large ice concentrations (> 90%), and nearly ignored those with very low ice concentrations (< 20%). In addition, a significantly higher amount of melt ponds was observed in the PAS in the summer of 2008 as compared to five years ago. The areally averaged albedo increased from 0.09 in the marginal ice zone at 77°N to 0.63 in the far north zone at 86°N, where the ice concentration was 90%. The albedo was significantly smaller than those reported in earlier studies in the PAS for the same region because of an overall decrease in ice concentration. Compared with 2007 data, the lower ice concentration in 2008 may yield a smaller total ice-covered area, although the Arctic ice extent in 2008 was slightly larger than the record minimum in 2007.