A Method for Deriving All‐Sky Evapotranspiration From the Synergistic Use of Remotely Sensed Images and Meteorological Data

Evapotranspiration (ET) is an important component of the water and energy cycle. The present study develops a practical approach for generating all‐sky ET with the synergistic use of satellite images and meteorological data. In this approach, the ET over clear‐sky pixels is estimated from a two‐stage land surface temperature (LST)/fractional vegetation cover feature space method where the dry/wet edges are determined from theoretical calculations. For cloudy pixels, the Penman‐Monteith equation is used to calculate the ET where no valid remotely sensed LST is available. An evaluation of the method with ET collected at ground‐based large aperture scintillometer measurements at the Yucheng Comprehensive Experimental Station (YCES) in China is performed over a growth period from April to October 2010. The results show that the root‐mean‐square error (RMSE) and bias over clear‐sky pixels are 57.3 W/m2 and 18.2 W/m2, respectively, whereas an RMSE of 69.3 W/m2 with a bias of 12.3 W/m2 can be found over cloudy pixels. Moreover, a reasonable overall RMSE of 65.3 W/m2 with a bias of 14.4 W/m2 at the YCES can be obtained under all‐sky conditions, indicating a promising prospect for the derivation of all‐sky ET using currently available satellite and meteorological data at a regional or global scale in future developments.