Satellite Remote Sensing of Permafrost and Seasonally Frozen Ground

Permafrost consists of ground materials that have remained at or below O°C for two or more years, while seasonally frozen ground refers to ground that freezes and thaws annually. Permafrost and seasonally frozen ground parameters are difficult to measure directly from remote sensing data since they are related to subsurface phenomena. Until recently, relatively few studies had examined the potential of remote sensing techniques for mapping the spatial distribution of near-surface permafrost, the properties of the active layer (the uppermost portion of the ground that freezes and thaws on an annual basis), and seasonally frozen ground in non-permafrost regions. In addition, few studies had made use of satellite imagery to map features indicative of the presence of near-surface permafrost or of the occurrence of permafrost degradation. Currently, high-resolution satellite images, such as those generated by sensors on board the IKONOS and QuickBird satellites, as well as declassified images generated by the CORONA spy satellite, are being used in conjunction with older aerial photographs to identify changes that have occurred in permafrost terrain in recent decades. Some of the most important advances in recent years have involved (1) the use of parameters related to permafrost conditions (including digital databases of topography and surface cover) to indirectly infer permafrost conditions over large areas by using remote-sensing classification algorithms and ground-truth data and (2) the development of active and passive microwave techniques to monitor near-surface soil freeze/thaw status at regional to continental scales. These recent advances, as well as potential areas of future development, are covered in this chapter.