Temporal evolution of Arctic sea ice surface temperature and thin ice types from airborne thermal infrared imaging during the winter 2019/2020 MOSAiC expedition

Abstract:

During the MOSAiC expedition thermal infrared imaging from a helicopter is used to measure the brightness temperature of sea ice and ocean water surfaces. Thin ice and open water areas dominate the heat exchange between the ocean and atmosphere during wintertime. This influences the Arctic Climate and becomes even more important in the currently changing Arctic. The sea ice gets thinner, moves faster, and breaks up easier. Observations with high accuracy of parameters like thin ice area or lead fraction are needed for a better understanding. In our study, a thermal infrared camera is flown on a helicopter in 43 flights. The measured surface temperature is evaluated up to a regional scale during the winter legs of the MOSAiC expedition. Two helicopter survey types were conducted: (i) a series of detailed survey flights of the MOSAiC floe and central observatory and (ii) repeated regional flights within the distributed network of autonomous buoys around the ship. We can resolve the surface in a georeferenced map with 1 m grid resolution where several hundred images are combined. Based on the temperature distribution we can conduct a surface classification for thin ice and open water. The temporal evolution of the surface conditions can be determined. This allows us to investigate the spatial and temporal variability of the thin ice areas. The conversion of the measured brightness temperature into an actual physical temperature requires knowledge of the surface properties as well as information about atmospheric conditions. The derived physical temperature is an important parameter for analyzing the heat exchange between ocean, ice, and atmosphere on different spatial and temporal scales. This knowledge will be used to compare and evaluate the thin ice or lead coverage as well as the ice surface temperature with satellite products. Based on these results, a new understanding of the variability of the ocean to atmosphere heat flux in the Arctic can be developed.