Estimation of spatial evapotranspiration over non-irrigated agricultural areas using a two-source energy balance model
Date
2009-11
Authors
Geli, Hatim M. E., author
Neale, Christopher M. U., author
U.S. Committee on Irrigation and Drainage, publisher
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Abstract
Spatial estimation of evapotranspiration (ET) from satellite imagery is important in agricultural studies because it provides information about the spatial variability of crop growing patterns and health, as well as for crop water requirements. The two-source energy balance model is one of the techniques used successfully in estimating ET spatially, through the estimation of surface energy fluxes such as sensible heat flux H, soil heat flux G, net radiation Rn, and latent heat flux LE, the latter being extrapolated to daily ET. The current study applies the two-source model to rain fed agricultural field located in the Walnut Creek watershed south of Ames, Iowa. Landsat TM images used to perform the analysis with the support of ground based data were acquired during the SMACEX project conducted in the summer of 2002. A visual basic interface called SETMI was programmed to interact with ArcGIS and perform the analysis spatially. A footprint model was used to compare the estimates of the different fluxes with measurements from eddy covariance flux towers. Two different closure methods were used to overcome the lack of closure problem in the eddy covariance measurements. Generally, the results show good agreements between the measurements and the estimates. The results show an underestimation of sensible heat flux with RMSE of 30 (Wm-2) and latent heat flux with RMSE of 45 (Wm-2). The net radiation and the soil heat flux shows RMSE of 17 (Wm-2) and 29 (Wm-2), respectively. The daily ET resulted in a RMSE of 0.71 (mm/day) and BIAS of -0.29 (mm/day).
Description
Presented at the fifth international conference on irrigation and drainage, Irrigation and drainage for food, energy and the environment on November 3-6, 2009 in Salt Lake City, Utah.