Estimation of regional evapotranspiration and soil moisture conditions using remotely sensed crop surface temperatures

Crop surface temperature gives information on the evapotranspiration rate and on soil moisture conditions. The use of crop surface temperatures remotely sensed by infrared line scanning (IRLS) can provide this information over large hydrologically nonuniform areas. A composite method has been developed to calculate actual evapotranspiration rates from remotely sensed crop surface temperatures, with the aid of the energy budget equation and aerodynamic heat and water vapor transport equations, while incorporating soil-plant-water relations. This method has been tested for grassland in an area near Losser, in the eastern part of the Netherlands. In this area, drought damage occurs due to groundwater extraction for drinking-water supply. A way to analyze accuracy was established. This analysis did show small standard deviations for measurements of evapotranspiration near the potential level, and a doubling of standard deviations when evapotranspiration approaches zero.