中文摘要：

多年冻土和季节冻土分别占北半球裸露地表的24％和55％。近地表土壤冻融的范围、冻结起始日期、持续时间及冻融深度对寒季／寒区植物生长、大气与土壤间能量、水分及温室气体交换都具有极其重要的影响。自20世纪70年代以来，应用卫星遥感结合地面观测资料研究局地到区域尺度的季节冻土和多年冻土已取得诸多成果，而遥感在冻土研究中的最直接应用是利用微波探测近地表土壤冻融状态。相对于主动SAR，星载被动微波传感器具有多通道观测且重访周期较高，空间分辨率很低的特点。重点评述了近几十年来被动微波辐射计在冻土研究中的算法发展及其应用前景，主要包括双指标算法、时间序列变化检测算法及判别树算法3类，其核心均是基于冻土的低温特征和“体散射变暗”效应。发展可靠实用的微波遥感土壤冻融状态判别算法，提供区域和全球尺度上的土壤冻融状态信息，对水文学、气象学以及农业科学、工程地质研究与应用都具有重要意义。

英文摘要：

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, water and greehouse gas ex- changes 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 re- gional scales with some successes. However, the direct application of remote sensing in the frozen ground research is to us the passive microwave brightness temperature to detect the soil freeze/thaw cycle. Compared to the active SAR, the spaceborne radiometers has the ability of multi-channels observation with frequent revisiting period, but with coarser spatial resolution. As the succession of the review, this paper focuses on the algorithm development and potential application of passive microwave radiometers in detecting near surface soil freeze/thaw cycle. The three widely used algorithms include dual-index algorithm, change detection algorithm based on the time series of brightness temperature and the decision tree algorithm. All three algorithms are based on low-temperature character- istics and volume scattering darkening effect of frozen soil. These algorithms are highly promising in detecting sur- face soil freeze/thaw status. However, further algorithm refinement, calibration and validation are needed.