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United States Department of Agriculture

Agricultural Research Service

Research Project: USING REMOTE SENSING & MODELING FOR EVALUATING HYDROLOGIC FLUXES, STATES, & CONSTITUENT TRANSPORT PROCESSES WITHIN AGRICULTURAL LANDSCAPES Title: A comparison of the eddy covariance, bowen ratio, and lysimetry-based measurements of surface energy fluxes during BEAREX08

Authors
item Alfieri, Joseph
item Kustas, William
item Prueger, John
item Chavez, Jose -
item Evett, Steven
item Neale, Christopher -
item Anderson, Martha
item Hipps, Lawrence -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 2010
Publication Date: September 27, 2010
Citation: Alfieri, J.G., Kustas, W.P., Prueger, J.H., Chavez, J.L., Evett, S.R., Neale, C., Anderson, M.C., Hipps, L.E. 2010. A comparison of the eddy covariance, bowen ratio, and lysimetry-based measurements of surface energy fluxes during BEAREX08 [abstract]. Remote Sensing and Hydrology 2010 Symposium. 2010 CDROM.

Technical Abstract: Understanding the accuracy and limitations of ground truth data is a critical prerequisite for assessing the quality of remote sensing-based products or models. Using data from the 2008 Bushland Evapotranspiration and Agricultural Remote Sensing Experiment (BEAREX08), this research sought to characterize the differences in three methods commonly used to estimate surface energy fluxes, particularly the latent heat flux ('E), i.e. evapotranspiration (ET). These methods include the eddy covariance (EC), Bowen ratio energy balance (BREB), and lysimetry-based (LY) methods. Each of these methods yielded different estimates of the surface fluxes. For example, under strongly advective, the measurements of 'E by the various methods differed by as much as 400 W m-2, or, equivalently in terms of ET, 0.6 mm hr-1. Similar differences were found for the sensible heat flux (H). The non-turbulent components of the surface energy budget, the net radiation (Rn) and soil heat flux (G), tended to vary less; the differences among the measurements of these quantities were typically less than 150 W m-2. The differences among the measurement systems are likely due to instrument errors, the assumptions and theoretical considerations underpinning each of the techniques and differences in the source area or contributing fetch for each of the methods. While it is assumed that the surface is homogeneous, spatial variations in the surface properties sampled by each of the three methods contributes to the mismatch among the measured fluxes. High resolution aircraft-based imagery mapping the spatial variability in canopy cover and moisture combined with flux-footprint/source-area analyses of the contributing area from each of the techniques provide more clues as to the factors causing discrepancies among the measurement systems. The results of this study underscore the uncertainty in measurements of energy and moisture fluxes that must be recognized when evaluating energy balance and evapotranspiration models.

Last Modified: 10/22/2014
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