水分亏缺指数在全国干旱遥感监测中的应用研究

APPLICATION OF WATER DEFICIT INDEX IN DROUGHT MONITORING IN CHINA WITH REMOTE SENSING

水分亏缺指数(WDI)是建立在作物水分胁迫指数理论基础上,并假设陆地表面温度是冠层温度与土壤表面温度线性加权及土壤与植被冠层之间不存在感热交换的情况下,结合陆气温差与植被指数得到的区域干旱评价指标。本文利用MODISTerra陆地表面温度和植被指数数据产品,采用NDVITs空间法分别计算了2000年4月上旬和5月中旬气温空间分布的基础上,结合陆气温差和植被指数计算全国范围WDI,并与表层土壤含水量进行对比。结果表明:WDI能够比较合理地用来监测区域干旱,不仅适用于裸地条件,还能够有效地应用于完全植被或部分植被覆盖条件下的干旱监测,克服了CWSI只能应用于郁闭植被冠层的限制。

Crop Water Stress Index (CWSI) that was firstly suggested by Jackson and Idso to evaluate water status was expressed as a function of (T_c-T_a). Since remote sensed thermal radiation is a mixture information of soil and canopy, CWSI is not applicable at the pixel scale. On the assumption that land surface temperature (T_s) is a linear function of canopy temperature (T_c), soil surface temperature (T_ soil) and vegetation cover fraction (f_v) and that there is no coupling between soil and canopy, Water Deficit Index (WDI) that was extended from CWSI was used to evaluate regional drought. In the paper, air temperature (T_a) spatial patterns in the first ten days of April and second ten days of May in 2000 were firstly figured out with NDVI-T_s (where NDVI is Normalized Difference Vegetation Index) space with Terra MODIS land surface temperature and vegetation index product. Then Water Deficit Index (WDI) was calculated based on (T_s-T_a) and NDVI. The comparison between WDI and topsoil moisture show that WDI can reach a satisfactory estimation of field water deficit for both full-covered and partially vegetated sites and have overcome the shortage of CWSI that can only work for the site of fully covered by vegetation.