APPLICATION OF SATELLITE REMOTE SENSING TECHNIQUES TO FROZEN GROUND STUDIES

摘要

Permafrost and seasonally frozen ground regions occupy approximately 24% and 55%, respectively, of the exposed land surface in the Northern Hemisphere. The areal extent, timing, duration, and depth of the near-surface soil freeze and thaw have a significant impact on plant growth, energy, and water and trace gas exchanges between the atmosphere and the soils in cold seasons/cold regions. Satellite remote sensing combined with ground "truth" measurements have been used to investigate seasonally frozen ground and permafrost at local to regional scales with some success. The objective of this paper is to provide an overview of satellite remote sensing techniques applied to study seasonally frozen ground and permafrost over the last few decades. Remote sensing of permafrost terrain and surface freeze/thaw cycles typically uses a combination of imaging in optical and thermal wavelengths, passive microwave sensing, and active microwave remote sensing using scatterometer and Synthetic Aperture Radar (SAR). No single sensor is capable of providing the range of observations needed. SAR imaging provides information on the timing, duration, and regional progression of the near-surface soil freeze/thaw status in cold seasons/regions with a relatively high spatial resolution, but repeat times of existing satellites are relatively long compared to the rate of change of the soil freeze/thaw cycle in fall and spring. Spaceborne passive microwave sensors offer more frequent coverage at several wavelengths, but with substantially lower spatial resolution. Optical and thermal sensors provide a middle ground in spatial resolution and temporal sampling between SAR and passive microwave satellites, but a known relationship between permafrost (and freeze/thaw depth) and corresponding environmental factors needs to be provided. Overall, microwave remote sensing is a promising technique for detecting near-surface soil freeze/thaw cycles over snow-free land. The potential for using land surface temperature derived from satellite visible and near-infrared sensors to study soil freezing and thawing processes is substantial. Satellite remote sensing data products—such as for snow cover extent, snow depth, snowmelt, land surface type, Normalized Difference Vegetation Index (NDVI), surface albedo, surface wetness, and soil moisture—can be very helpful for frozen ground studies at local, regional, and global scales.