Ricardo Trezza

Estimation Of Evapotranspiration From Satellite‐Based Surface Energy Balance Models For Water Management In The Rio Guarico Irrigation System, Venezuela

This paper explores the feasibility of the use of two energy balance models for the estimation of evapotranspiration from satellite data in a large irrigated area. The Rio Guarico irrigation system is located in the State of Guarico in Venezuela. A large water reservoir stores the water coming from the Guarico River and provides water for irrigation to an area of near 60,000 hectares. Rice is the main crop grown in the area.One of the models used in this study was SEBAL (Surface Energy Balance Algorithm for Land), which is an image‐processing model for calculating evapotranspiration (ET) as a residual of the surface energy balance. SEBAL was developed in the Netherlands by Bastiaanssen and has been applied in many developing countries. SEBAL uses satellite data collected by the LANDSAT Thematic Mapper (TM) or other satellite sensors collecting visible, near‐infrared and thermal infrared radiation. The main advantage of SEBAL is the need of a minimum amount of ground data. The second model applied was METR...

Why Use Reference Evapotranspiration to Calibrate Satellite-based Energy Balances?

Satellite-based surface energy balance has become a very useful tool for determining actual evapotranspiration (ET) over large areas. Major uncertainties in derived ET exist, however, due to error and bias introduced to the surface energy balance and ET by components of the energy balance. These biases include biases in atmospheric correction, albedo calculation, net radiation calculation, thermal band and surface temperature, air temperature gradient used in sensible heat flux calculation, soil heat flux function, and extrapolation to 24-hour and longer periods. At the University of Idaho, we use calculated hourly reference evapotranspiration (ET r ) to calibrate the surface energy balance during processing to remove a majority of these biases. The ET r method uses alfalfa reference ET calculated with the ASCE-EWRI standardized Penman-Monteith equation. Experience and field verification with this method has created confidence in using ET r for image calibration rather than using available energy only. In addition to its use to calibrate the energy balance, ET r is used to extrapolate ET images to 24hour and longer periods. The use of ET r provides equivalency and congruency with ET as estimated using the traditional crop coefficient x ET r approach. With Landsat images, full-cover alfalfa or other high leaf area vegetation can be identified, and ET from these fields is expected to be near the value of alfalfa ET r . Comparisons between ET by METRIC, ET by lysimeter and ET by traditional methods suggest that METRIC or similar methods hold promise as efficient, accurate, and inexpensive procedures to predict actual evaporation fluxes throughout a growing season.