近10 年我国地表比辐射率的时空变化

基于Terra-MODIS L3 级产品MOD11C3,得到2001-2010 年10 年我国地表比辐射率时空数据集。结果表明,我国地表比辐射率最小的区域是西北沙漠地带,该区域比辐射率一年四季变化不大、分布范围固定。东北地区和北疆地区、青藏高原地区、长江中下游和华东华南地区等区域比辐射率变化明显。冬季,东北地区、北疆地区地表比辐射率比较大。青藏高原地区11 月-次年3 月维持在一个中低比辐射率水平,其他月份比辐射率则呈现增大趋势。长江中下游、华东、华南和四川盆地地区的比辐射率7-10 月减小,其中8 月份面积达到最大。低比辐射率区(0.6163~0.9638)、中低比辐射率区(0.9639~0.9709)、中比辐射率区(0.9710~0.9724)所占面积都不大,分别维持在20%、10%、20%左右;中高比辐射率区(0.9725~0.9738) 所占范围最大,达到我国陆地面积的40%~50%,且变化十分明显,表现出明显的波峰、波谷变化,春季和秋季是波峰、夏季和冬季是波谷;高比辐射率区(0.9739~0.9999) 面积变化也很明显,冬季是一个明显的波峰,面积可达10%,而其他季节则维持在1%、2%以下。我国地表比辐射率时空分布与温度之间呈现一定的相关关系,比辐射率越高、气温越低。

Spatial-temporal Changes of Land Surface Emissivity in China from 2001 to 2010

The land surface emissivity is one of the important parameters in temperature inversion from thermal infrared remote sensing. With the aid of MOD11C3 of Terra-MODIS L3 level products, we obtained 10-year spatial-temporal data sets of land surface emissivity in China from 2001 to 2010. The results show that Northwest China’s desert region has the minimum land surface emissivity in China, with little seasonal variations. In contrast, there are significant seasonal variations in land surface emissivity in Northeast and Northwest China, Qinghai-Tibet Plateau, the Yangtze River Basin, East and South China. In winter, the land surface emissivity is relatively high in Northeast and Northwest China. The land surface emissivity of Qinghai-Tibet Plateau maintains a lower value from November to March, while it is higher in other months. The land surface emissivity of the Yangtze River Basin, East China, South China and Sichuan Basin decreases from July to October, and peaks in August. Land surface emissivity values could be divided into five levels: low emissivity (0.6163-0.9638), low-moderate emissivity (0.9639-0.9709), moderate emissivity (0.9710-0.9724), moderate-high emissivity (0.9725-0.9738), and high emissivity (0.9739-0.9999). The percentages of regions with low emissivity, low-moderate emissivity and moderate emissivity are, respectively, about 20% , 10% and 20% . The moderate-high emissivity regions makes up of 40%-50% of Chinese surface land area. The inter-annual variation of moderate-high emissivity region is also distinct, with two peaks (in spring and autumn) and two troughs (in summer and winter). The inter-annual variation of high emissivity regions is very significant, with a peak in winter (10%), while only 1% and 2% in other seasons. There is clear relationship between the spatial-temporal distribution of Chinese land surface emissivity and temperature: the higher the emissivity, the lower the temperature, and vice versa. Emissivity is an inherent property of any object, but the precise value of its emissivity depends greatly on its surrounding environmental factors.