Mapping ET at High Resolution in an Advective Semi-Arid Environment with Airborne Multispectral Imagery

Periodic and accurate estimates of spatially distributed evapotranspiration (ET) are essential for managing water in irrigated regions and in hydrologic modeling. In this study, METRIC (Mapping ET at high Resolutions with Internal Calibration), an energy balance algorithm originally developed for application with Landsat imagery at a regional scale, was applied to very high resolution aircraft imagery (0.5–2 m pixels) in the Texas High Plains. ET predictions were evaluated using data from four large precision weighing lysimeters located in the USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas. Statistical results indicated that METRIC worked better for crops with leaf area index greater than 2.5 m² m^–2. Potential limitations may have been the areal extent of the imagery, the surface roughness for the momentum transfer sub-model, and the lack of a cold pixel with characteristics similar to the reference crop, i.e. alfalfa.