Remote detection of bare soil moisture using a surface-temperature-based soil evaporation transfer coefficient

Abstract An approach for estimating soil moisture is presented and tested by using surface-temperature-based soil evaporation transfer coefficient ( h a ), a coefficient recently proposed through the equation h a =  ( T s  −  T a )/( T sd  −  T a ) , where T s , T sd , and T a are land surface temperature (LST), reference soil (dry soil without evaporation) surface temperature, and air temperature respectively. Our analysis and controllable experiment indicated that h a closely related to soil moisture, and therefore, a relationship between field soil moisture and h a could be developed for soil moisture estimation. Field experiments were carried out to test the relationship between h a and soil moisture. Time series Aqua-MODIS images were acquired between 11 Sep. 2006 and 1 Nov. 2007. Then, MODIS derived h a and simultaneous measured soil moisture for different soil depths were used to establish the relations between the two variables. Results showed that there was a logarithmic relationship between soil moisture and h a ( P 3 /cm 3 and 0.0503 cm 3 /cm 3 for surface energy balance method at two soil depths (10 cm and 20 cm), with RMSE of 0.0467 cm 3 /cm 3 and 0.0581 cm 3 /cm 3 for maximum temperature method at two soil depths. For vegetated surfaces, the ratio of h a and NDVI suggested to be considered. The proposed approach has a great potential for soil moisture and drought evaluation by remote sensing.