Estimation of soil moisture using trapezoidal relationship between remotely sensed land surface temperature and vegetation index

The trapezoidal relationship between land surface temperature (T-s) and Vegetation Index (VI) was used to estimate soil moisture in the present study. An iterative algorithm is proposed to estimate the vertices of the T-s similar to VI trapezoid theoretically for each pixel, and then Water Deficit Index (WDI) is calculated based on the T-s similar to VI trapezoid using MODIS remotely sensed measurements of surface temperature and enhanced vegetation index (EVI). The capability of using WDI based on T-s similar to VI trapezoid to estimate soil moisture is evaluated using soil moisture observations and antecedent precipitation in the Walnut Gulch Experimental Watershed (WGEW) in Arizona, USA. The result shows that, the T-s similar to VI trapezoid based WDI can capture temporal variation in surface soil moisture well, but the capability of detecting spatial variation is poor for such a semi-arid region as WGEW.