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United States Department of Agriculture

Agricultural Research Service

Title: Evaluating airborne remote sensing ET estimates using eddy covariance systems and a heat flux source area function.

Authors
item Chavez Eguez, Jose
item Howell, Terry
item GOWDA, PRASANNA
item Neale, Christopher - UTAH STATE UNIV.
item COLAIZZI, PAUL

Submitted to: Irrigation Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 21, 2008
Publication Date: November 2, 2008
Citation: Chavez Eguez, J.L., Howell, T.A., Gowda, P., Neale, C.M., Colaizzi, P.D. 2008. Evaluating airborne remote sensing ET estimates using eddy covariance systems and a heat flux source area function. Irrigation Association Conference Proceedings, November 2-4, 2008, Anaheim,California. 2008 CDROM.

Interpretive Summary: Agriculture, cities, and industries are increasingly competing for water resources. Thus, saving water by managing irrigation systems better may save water for other uses. Irrigation may potentially become more efficient if irrigation scheduling is improved. This improvement could be attained by using accurate crop water use or evapotranspiration maps. We estimated evapotranspiraiton using a modified two source energy balance model. Other inputs included weather station data and images of ground surface reflectance and temperature acquired with an aircraft. We evaluated the evapotranspiration maps with measured data from the 2008 Bushland Evapotranspiration and Agricultural Remote Sensing Experiment. The experiment took place at the USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas. Predicted evapotranspiration values, for cotton fields, were compared with measured data using eddy covariance systems. Results showed that the modified two source model slightly under estimated evapotranspiration by 5.1%, with a small variability of 7.2%. The modified two source model performed well for the early cotton development period.

Technical Abstract: The use of water for production of crops must become more efficient as competition for water increases. Thus, saving water by managing irrigation systems better may be possible if irrigation scheduling is improved by accurately estimating spatially distributed actual evapotranspiration (ET). ET can be estimated using energy balance algorithms that use agrometeorological and remote sensed surface reflectance/temperature data. In this study, the objective was to evaluate spatial ET estimates obtained with a modified energy balance-based Two Source Model (TSM). For this purpose, two high-resolution aircraft images acquired during the 2008 Bushland Evapotranspiration and Agricultural Remote Sensing Experiment (BEAREX08) at the USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas, were used. Predicted ET values for cotton fields were compared with measured ET from eddy covariance systems using a heat flux source area function. Results showed that the TSM slightly under estimated ET by 0.5 mm d**-1, (or -5.1%) with a standard deviation of 0.6 mm d**-1. Overall, the modified TSM performed well for LAI values less than 1.5 m**2 m**-2.

Last Modified: 7/28/2014
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