| Evapotranspiration is an important component of the hydrologic cycle. The regional assessment by conventional techniques needs many measurements, equipment, and manpower to measure the factors that control the evaporation process. The potential of remote sensing to provide these factors is promising. Therefore, the present work was conducted to assess the potential for remote sensors to collect the data necessary for estimating evapotranspiration rates and to evaluate the accuracy of detecting the factors that control the process. A model was formulated by combining the energy balance and the aerodynamic and surface resistances to the vapor flux with the consideration of the stability conditions of the atmosphere. Furthermore, an error analysis has been performed to study the accuracy of future remote sensor systems to detect the model variables. Data used in this research were collected from Phoenix, Arizona, and Scotts Bluff, Nebraska, for bare soil and sugar beet, respectively. The model provides good estimates of evaporation/transpiration rates on an hourly basis. The model provided accurate predictions for long-term total evaporation when compared with measured lysimetric data. The error analysis shows that the overall sugar beet transpiration error is 0.172 mm/hr when all of the input variables are detected with certain accuracies. These accuracies were assessed using sensitivity analyses for all of the input variables. Additionally, sensitivity analyses indicated that the wind speed, air temperature, and surface vapor pressure are relatively important in estimating evapotranspiration rates. |
