Stationary and Moving Wireless Infrared Thermometers to Calculate Crop ET

A wireless infrared thermometer (IRT) system was developed by USDA-ARS and commercialized by a manufacturer. The system was specifically designed for deployment in agricultural fields to measure canopy and soil temperatures, and has been used to detect and map crop water stress, crop evapotranspiration (ETc), and other biotic stress. We report calculation of ETc using the commercially available system, which was deployed over large weighing lysimeters and aboard center pivots at USDA-ARS, Bushland, Texas, USA. Soil and canopy temperatures measured by the IRTs and micrometeorological data were input to a two-source energy balance (TSEB) model to calculate ETc. Independent measurements and estimates of ETc were obtained, respectively, from the weighing lysimeters and a soil water balance using field-calibrated neutron probes. Discrepancies between ETc calculated by the TSEB and ETc obtained by independent methods resulted in root mean squared error up to 1.8 mm per day, mean absolute error up to 1.5 mm per day, and mean bias error within ± 0.65 mm per day. Over fifty and eighty percent of the irrigated area in the US and Southern Great Plains, respectively, is now by center pivot. Therefore, the wireless IRT system using center pivots as a platform provides a new opportunity to manage irrigated crops, water resources, and represents a new data source for atmospheric and hydrologically-coupled models.