植被含水量估算在作物灌溉和森林火灾预警中具有重要指导意义。采用8天合成MODIS地表反射率数据,针对植被水分含量与陆表水指数,植被覆盖与归一化植被指数的关系及不同植被类型和地表水分含量状况在NDVI-LSWI二维空间中的分布规律,在NDVI-LSWI梯形特征空间中确定最大和最小含水量边界线的基础上采用植被干燥指数直接估算植被水分亏缺程度。该方法不仅简便,而且可以避开植被指数温度梯形图中陆地表面温度和气温差值的测量。
Estimating the water status of vegetation is most important in crop irrigation and prediction of forest fire. This paper analyzes the relationships between vegetation water content (VWC) and land surface water index (LSWI) and between fractional vegetation cover and normalized difference vegetation index (NDVI) from 8-day composite MODIS (Moderate Resolution Imaging Spectroradiometer) surface reflection products (MOD09A1), and the distribution regularities of different type of vegetation and its surface water content in LSWI-NDVI space. Two years’ 8-day composite MODIS Surface Reflection products were used to estimate the minimal and maximal water content lines of the hypothetical trapezoidal shape of NDVI-LSWI in the study area. Instead of the theoretical trapezoidal shape of fractional vegetation cover and Ts-Ta that indirectly estimated water status per fractional vegetation cover (Ts-Ta is surface (soil and canopy) temperature minus air temperature at measuring time), the vegetation dryness index (VDI) developed in this study was directly used to estimate vegetation water deficits at the canopy level by the trapezoidal shape of LSWI-NDVI. The technique simply estimated vegetation water status without measuring Ts-Ta.
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