Radar image from Japan’s ALOS-2 satellite of the sea ice near the Polarstern icebreaker. Polarstern is drifting in the Arctic sea ice for a year for the MOSAiC polar research expedition. During the polar winter, the researchers use radar satellite images such as this to monitor the sea ice in the surrounding area. In this false-colour image, which was acquired on 19 November 2019, dark blue cracks show open water leads or thin ice between the ice floes. The white filament-like structures are typically sea-ice ridges or other deformed sea ice.