For the first time since the restrictions imposed due to the Coronavirus pandemic, flights of the Polar 5 and Polar 6 research aircraft are currently taking place from Longyearbyen airport on the island of Spitsbergen to the central Arctic. Both aircraft are operating as part of the MOSAiC expedition led by the Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research to study the polar atmosphere and sea ice. The high-resolution Modular Aerial Camera System (MACS) and scientists from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) are on board. The researchers are particularly interested in how the thickness of the sea ice currently under investigation develops and how changes in the ice sheets can be more easily identified. DLR atmospheric researchers are also involved in the project and want to find out how clouds form over the Arctic Ocean.
From Mount Everest to the Arctic
An earlier version of the MACS camera system has already provided highly detailed, 3D images of ice and snow under the extreme environmental conditions around Mount Everest in the Himalayas. "We have now used this experience to develop an advanced camera instrument for remote sensing of polar regions, which, in addition to a channel for visible light, also has channels for near-infrared and thermal-infrared radiation," says Jörg Brauchle from the DLR Institute for Optical Sensor Systems in Berlin who is flying on board Polar 6. "In this way, we are closing the gap between very costly, detailed exploration on the ground and large-scale, but lower-resolution, remote sensing data acquired from space."
Observations made from the air using MACS make it possible to automatically determine the degree of ice coverage on the water with very high resolution. The optical images also help researchers to determine the roughness of the ice and snow in order to better characterise and classify them both and to better understand the processes at play in sea ice. The near-infrared images are used for the automatic detection of water and ice floes, while the thermal-infrared images allow improved detection of temperature differences between ice and the surrounding environment as well as freezing fissures. Thanks to the high recording rate of four images per second, it is possible to record everything under the aircraft without interruption, even during low flights just 100 metres above the surface. Details as small as two centimetres across can be identified.
The scientists acquired more than 300,000 images with MACS during the first flights at the beginning of September. "Even with the currently very small differences in temperature between water and ice, clear thermal signatures can be identified," Brauchle emphasises. "Even greater temperature differences can be expected during the use of the camera in one of the upcoming winter expeditions, which the powerful thermal sensor will document." The detailed information about the surface ice will help to improve climate models and serve as a training basis for new AI methods that will be used to evaluate the large number of images. In addition to the documentation of the surface properties of the sea ice, an electromagnetic measuring system (EM-Bird) from AWI on board Polar 6 is being used to measure sea ice thickness.
Droplet size distribution and analyses of ice crystal shapes for cloud research
While Polar 6 measures the sea ice in the Arctic Ocean, the Polar 5 crew is concentrating on studying the atmosphere and clouds above the Arctic Ocean. Previous studies have shown that clouds contribute significantly to the rapid warming of the Arctic region. However, modern atmospheric models have so far underestimated the influence of clouds and still simulate it too imprecisely. For this reason, the team of researchers from AWI, DLR and the universities of Leipzig, Bremen, Cologne, Mainz, and Clermont Auvergne are studying the air masses over the Arctic Ocean on a large scale and investigating in detail all the factors relevant to cloud formation. "On board Polar 5 we are measuring microphysical cloud properties such as droplet size distribution, phase, ice and liquid water content, and the shapes of ice crystals," explains Valerian Hahn from the DLR Institute of Atmospheric Physics. "Another main focus is on Arctic mixed-phase clouds," adds Manuel Moser from the same institute. As they make their measurements of the Arctic air, the researchers are also following the route previously taken by the German research icebreaker, Polarstern, as part of the MOSAiC campaign.