abstract:
Remotely measuring evapotranspiration (ET) and separating its two components, soil evaporation (E) and vegetation transpiration (T), have been challenges for ET study and application. In this study, a three-temperatures model (3T model) based on thermal remote sensing is developed, verified, and applied for ET estimation under a multi-scale condition. There are two sub-models in the 3T model: soil evaporation sub-model and vegetation transpiration sub-model. E and T can be separately estimated by these two sub-models, and then ET can be obtained to put E and T together. One of the most significant advantages of the 3T model is that only a minimum amount of data are required. The necessary parameters are net radiation, soil heat flux, surface temperature (dry soil and drying soil), and air temperature for E estimation, while it is net radiation, surface temperature (canopy and reference canopy), and air temperature for T estimation. Verifications and applications were carried out by using ground and space based thermal remote sensing, varying from leaf scale (a few square centimeters) to catchment scale (over 10 thousand square kilometers). Verifications were carried out by comparing the estimated results with the measured ET from weighing lysimeter, Bowen ratio, Penman-Monteith, eddy covariance, and water budget. Results show that the approach of “3T model + thermal remote sensing” is a reliable and practical way for remotely measuring ET. Especially in arid and semi-arid regions, the method performs better. Therefore, it can be applicable for irrigation water management, water and energy budgets monitoring, thermal environment monitoring and evaluation, and other applications.