Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/6/2007
Publication Date: 12/10/2007
Citation: Gowda, P., Howell, T.A., Scanlon, B.R., Copeland, K.S., Bush, K.A. 2007. Preliminary evaluation of sensible heat flux measurements from a large aperture scintillometer using lysimetric data [abstract]. American Geophysical Union Fall Meeting, December 10-14, 2007, San Francisco, California. 2007 CDROM.
Technical Abstract: The path integrating capabilities of scintillometers over several kilometers make it a potential tool that can bridge the gap between primary point based observations (lysimeters, Bowen ratio, or eddy covariance) and the demand for large-scale spatially averaged surface fluxes. Further, the spatial scale of sensible heat flux data collected from a scintillometer is comparable to the spatial resolution of satellite images. Therefore, scintillometer data may be useful for validating evapotranspiration maps based on satellite data. Numerous studies have evaluated the measurement accuracy of scintillometers using eddy covariance systems; however, the latter has energy balance closure problems up to 30%. The main objective of this study is to test the Large Aperture Scintillometer (LAS) using lysimetric data. The LAS monitors the sensible heat flux (H) and water vapor flux (LE) is calculated as a residual of the surface energy balance equation by monitoring net radiation (Rn) and soil heat flux (G) (LE=Rn+G-H). A Large Aperture Scintillometer was deployed across two lysimeter fields planted with grain sorghum under dryland management conditions. The orientation of LAS was selected to have the path of the LAS perpendicular to the predominant wind direction and to avoid direct sunlight on the lenses. The refractive index of air was monitored during the 2007 cropping season at 15-min. intervals, synchronized with weather station and lysimeter measurements. In addition, a net radiometer and three soil heat flux plates were installed near both the receiver and transmitter of the scintillometer as well as on two large monolithic lysimeters. Predicted water vapor fluxes from the scintillometer-net radiometer-heat flux plate setup were compared with lysimeter data. Preliminary results (three months of data) indicate that the LAS is a promising tool for deriving water vapor fluxes. However, further evaluation is needed under a variety of crop/weather conditions to fully assess its capability to accurately estimate spatially distributed water vapor fluxes.