利用2010 年DOY 209 期的Terra/MODIS 16 d 合成的植被指数(EVI)产品数据MOD13 A2 和8 d 天合成的地表温度(LST)产品数据MOD11 A2,构建LST- EVI特征空间,从而得到了条件温度植被干旱指数TVDI反映的藏北土壤湿度空间分布图。结合野外同步土壤表层水含量测试数据,二者表现出较好的相关程度,并通过0.05 水平的显著性检验。对藏北地区土壤湿度的空间格局和分异规律分析,研究结果表明：①藏北全区TVDI值呈正态分布,东部地区偏湿,中部地区多数为正常湿度,而西部TVDI直方图分布形状与全区相似,但偏旱；②藏北地区不同气候区划内土壤湿度分异较大,那曲高山谷地亚寒带半湿润区土壤湿度最高,其空间变异也最强烈,青南高原亚寒带半干旱区土壤干旱最严重；③研究区内土壤湿度空间分布受海拔影响较为明显,在海拔4500 m以下的地区土壤湿度随海拔升高而降低,此后,土壤湿度随着海拔升高而升高。
Using enhanced vegetation index (EVI) and land surface temperature (LST) dataset derived from TERRA/MODIS synthetic products MOD13 A2 (16-day composite, DOY 209 in 2010) and MOD11 A2 (8-day composite, DOY 209 and 217 in 2010), the LST-EVI two-dimensional characteristic space was constructed, and then TVDI (temperature-vegetation drought index) was extracted to indicate the top-soil moisture of northern Tibet. Furthermore, the simulated soil moisture was verified by synchronously measured data in the field. The two groups of data showed a strong relationship and the correlation coefficient got through the 0.05 significance level. Then the spatial pattern and heterogeneity of soil moisture in the studied area were further analyzed, and the results showed: (1) the TVDI values of pixels in northern Tibet proved to have a statistically normal distribution, and the soil moisture in eastern region, central region and western region respectively showed wet, normal and dry situations; (2) evident difference in soil moisture existed in different climatic zones, and the soil moisture in the mountain and valley-in-valley structured Nagqu sub-arctic and sub-humid zone was the highest and that in southern Qinghai sub arctic and semiarid zone was the lowest; (3) the spatial distribution of soil moisture in the area was obviously affected by the altitude. The soil moisture in the region below 4500 m showed a negative correlation with the altitude and the correlation was positive in the region higher than 4500 m.
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