Monitoring surface soil moisture status based on remotely sensed surface temperature and vegetation index information

Surface soil moisture is a key variable for describing water and energy exchanges at the surface/atmosphere interface. The triangle or trapezoid method is appropriate for monitoring the regional surface soil moisture status. In this study, an advanced temperature vegetation dryness index (ATVDI) is used to monitor soil moisture status using an improved surface temperature and a vegetation index space that is formed by the theoretical dry edge determined by the surface energy balance principle and the wet edge extracted from water surface temperature. The ATVDI was validated by in situ soil moisture measurements from the Southern Great Plains (SGP) and is compared with a simple temperature vegetation dryness index (STVDI) estimated from the observed dry edge. The results indicate that the theoretical dry edge forms a trapezoid shape during the period of data coverage whereas the observed dry edge does not. Across all points, the R2 of the ATVDI (0.35) is greater than that for the STVDI (0.28). For almost all of the sites, the R2 between the ATVDI and soil moisture apparently improved. We also examined the spatial variation, and the value range of the ATVDI is closer than the STVDI to the real soil moisture conditions. The temporal variation of the ATVDI is closer to soil moisture than that of the STVDI, and the ATVDI is more sensitive to rainfall. This study demonstrates that a theoretical dry edge, determined by the energy balance principle, sets a standard for different days and that the ATVDI could monitor soil moisture conditions better than the STVDI could.