ET Mapping with High-Resolution Airborne Remote Sensing Data in an Advective Semiarid Environment

Accurate estimates of spatially distributed evapotranspiration (ET) are essential for managing water in irrigated regions and for hydrologic modeling. METRIC (Mapping ET at high Resolutions with Internal Calibration) energy balance algorithm was applied to derive ET from six high-resolution aircraft images (0.5–2.0 m pixels). Images were acquired over the USDA Agricultural Research Service (USDA-ARS) Conservation and Production Research Laboratory (CPRL) in the semiarid Southern High Plains. The remote sensing (RS) campaign occurred during the 2007 summer cropping season. Daily ET estimations were evaluated using measured ET data from five monolithic weighing lysimeters located in the CPRL. On average, errors in estimating hourly ET were -0.7±11.6%; for daily ET, errors were 2.4±9.3%. Results indicated that METRIC algorithm estimated ET values well when the surface roughness for momentum transfer considered heterogeneous surface conditions and when the grass reference ET fraction was used to extrapolate instantaneous estimates of ET. Results showed that it was possible to apply METRIC with airborne images in a semiarid environment. However, an appropriate (or combination of) surface roughness length and ET extrapolation methods have to be incorporated into the ET algorithm.