Estimating ground ice volumes in tundra polygon networks

As outlined in the previous IAF congress in Vancouver, global warming is a majorand growing concern in Arctic regions. Climatic changes in the polar regions of earth are believed to be at least twice as dramatic as in others. A wide international and interconnected approach to the investigation of its impacts is needed. Remote sensing of Arctic regions is unique as it can be used to provide periodic, reliable and precise datasets of any given region. Field research, on the other hand iscrippled by the remoteness, the cost, and the short time frame generally involved. While a considerable amount of research has been conducted on sea ice, sea surface temperatures, and sea currents, few studies have been focusing on the impacts of climate change on theland, and in particular on the permafrost that underlies the entire Arctic. This critical issue has to be addressed rapidly since it directly affects the Inuit communities, the flora, and the fauna of the Arctic.One singular component of the Arctic regions is the presence of tundra polygons, also termed patterned ground. Tundra polygons are linked to the thermal contraction ofthe ground at very low temperatures. They can be found on Earth and on Mars and are observable over large areas, delineating fractal-like networks on the ground. They are characterized by the presence of large quantities of ice at their edges. The imminenceof considerable warming of air temperatures in the Arctic will undoubtedly lead to the melting of most ice, subsequently inducing a lowering of the ground over thousands ofsquare kilometres. No method presently exists to automatically delineate these networks of polygons, and thereafter to quantify the volumes of ice. In this study we present the first attempt to quantify the volumes associated with the thermal contraction fractures and subsequently the volumes of ice present in the ground using high resolution imagery. We investigated several terrains in the western and high Canadian arctic and validated this method with intensive field campaigns. Geophysical methods including ground penetrating radar and capacitive-coupled resistivity were used to provide and in situ mapping of the subsurface, yielding the necessary calibration datasets.Ikonos 1 m imagery for several locations of the Arctic was used to process the algorithm developed at McGill University (Canada) and at the Alfred Wegener Institute (Germany) by the authors. A set of directional edge-enhancement filter combined with radiometric enhancements was applied to the images and yielded remarkably sharp and clear images of the polygonal networks. In addition, geophysical yield data proved to corroborate the patterns extracted by the algorithm. Further processing allowed us to make a first assessment of the volumes of ice associated with the polygons and subsequently of the potential settlement of the ground.The method could be extended to the study of mars polygons (MOC imagery) andsimilarly produced sharp images with clearly defined delineations of the network. This method emphasizes the crucial role played by satellite imagery in the study of climate change environmental impacts in remote Arctic regions. Current innovations including the launch of new high resolution sensors and constellations of such sensors will allow periodic and intensive studies of remote and inaccessible locations. In addition,this technique, by its universal component, can serve current reassessments of potential permafrost hazards in remote Arctic regions.

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