Effects of Directional Anisotropy of Thermal Infrared Temperature on Land Surface Evapotranspiration Estimation

Evapotranspiration (ET) plays an important role in a large range of applications in the fields of agriculture, hydrology and meteorology. Thermal infrared (TIR) land surface temperature (Ts) is a valuable metric for constraining ET. However, remote sensing-based Ts values corresponding to a scene viewed by different angles thus leading to different retrievals would bring directional anisotropy effect on ET estimation. In this paper, the anisotropy effect was evaluated at first by simulating the directional Ts with an integrated model named SCOPE (soil-canopy spectral radiances, photosynthesis, fluorescence, temperature and energy balance) in which the meteorological data at Yucheng site in China were used as driving data. Then ET were estimated with the surface energy balance system (SEBS) model using the simulated directional Ts. The ET differences with different directional Ts as input were analyzed for assessing the directional anisotropy effect on ET estimation. The analysis of the amplitude of anisotropy showed that the ET difference resulted from Ts anisotropy can reach up to 90 W/m
²
.