冻土遥感研究进展——可见光、红外及主动微波卫星遥感方法
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 freeze/thaw soil have a significant impact on the plant growth,energy,water and trace gas exchanges between the atmosphere and the soils in cold seasons and 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 successes.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 data in optical-thermal wavelengths,passive microwave sensing,and active microwave remote sensing(including the scatterometer and Synthetic Aperture Radar).Any single sensor is not 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 the revisiting period of existing satellites are relatively longer compared to 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.The optical-thermal sensors provide a compromise in spatial resolution and temporal sampling between SAR and passive microwave satellites,but a prior relationship between permafrost(and freeze/thaw depth) and corresponding environmental factors needs to be provided.Overall,microwave remote sensing is a promising technique to detect the near-surface soil freeze/thaw cycles over snow-free land.The potential of using land surface temperature derived from the thermal