A Full Satellite-Driven Method for the Retrieval of Clear-Sky Evapotranspiration

Abstract

Evapotranspiration (ET) plays an important role in the soil-vegetation-atmosphere system for its considerable effect in surface energy balance and water cycle. The determination of ET based on full satellite data has been a challenge. In the present study, a full satellite-driven method is proposed based on a newly developed pixel-to-pixel scheme of the land surface temperature-vegetation index trapezoidal feature space in the presence of clear-sky conditions. For the implementation of this approach, the three main meteorological parameters of net surface radiation, air temperature, and relative humidity were obtained solely based on satellite observations. With the exception of the three main satellite-derived meteorological parameters, different wind speed data—including actual measurements, the assimilated product, and an averaged value of meteorological observations—were used to investigate their effects on the retrieval of ET. Specifically, two pixel-to-pixel trapezoidal feature space schemes, namely an original and a two-stage scheme, were implemented to estimate ET over an arid region of the study area located in the northwest part of China. Comparison of the estimated ET with the values acquired from the eddy covariance systems yielded a reliable accuracy response with root-mean-squared errors of ~80 W/m2 and ~70 W/m2 for the original and two-stage trapezoidal methods with satellite-derived inputs, respectively, and constant wind speed data over the growing 2012 season from May to September. These results indicate that the full satellite-driven method is capable of estimating ET over the arid region of the study area.