Effects of the new Priestly-Taylor equation on determining the boundary of LST/FVC space for soil moisture monitoring

Abstract

Land Surface Temperature and Fractional Vegetation Coverage (LST/FVC) space is a classical model in remote sensing of soil moisture (SM). Its most vital issue is the determination of the boundary i.e. dry and wet edges. Visual interpretation and automatic fitting methods are very demanding for the research area. In contrast, theoretical calculation of the boundary has great application potential, where the traditional Priestley-Taylor (PT) equation has been introduced to derive a Sun2016 method. Recently, a new Priestly-Taylor equation was suggested. In order to furtherly improve the optical & thermal remote sensing of SM, we evaluated the new PT equation for boundary determination through deriving a Sun 2021 method. The evaluation was conducted using data from three aircraft experiments for SM observation i.e. SMAPVEX12, SMAPVEX16 in Iowa, and SMAPVEX16 in Manitoba. Simulated data with the Simsphere model was also used. Results demonstrated that the effects of the new PT equation are related to air temperature (Ta). For a certain range of Ta such as from 290 K to 310 K, the Sun 2021 method is close to the Sun2016 method, which implies limited influence of the new PT equation within that range. For Ta out of that range, the Sun 2021 method presented better performance than the Sun2016, which implies stronger suitability of the new PT equation. Sensitivity analysis indicated that the new PT equation increases the sensitivity of calculated wet edge to Ta while decreases its sensitivity to the other input variables. For future extensive application, we also explored convenient ways for determining some essential parameters in the Sun 2021 method. The new PT equation has potential to promote the optical & thermal remote sensing of SM, evapotranspiration, drought, etc.