Submitted to: Remote Sensing in Hydrology Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 9/30/2010
Publication Date: 9/28/2010
Citation: Gowda, P., Howell, T.A., Basu, S., Scanlon, B. 2010. Scintillometry for ET mapping applications: A lysimetric evaluation [abstract]. Remote Sensing and Hydrology Symposium, September 27-30, 2010, Jackson Hole, Wyoming. 2010 CDROM. Interpretive Summary:
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 heat fluxes. Further, the spatial scale of sensible heat fluxes (H) derived from a scintillometer is comparable to the spatial resolution of satellite images. Therefore, scintillometer data may be useful for validating evapotranspiration (ET) 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 was to evaluate the ability of the Large Aperture Scintillometer (LAS) for deriving ET using lysimeter data in the Texas High Plains. The study was conducted during 2008 and 2009 summer growing seasons in the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas. Field experiment consisted of three parts: (1) cross calibration of three LASs, (2) measurement of H over cotton (Gossypium hirsutum) managed under irrigated and dryland conditions, and (3) comparison of scintillometer-based ET measurements with lysimeter data. Cross calibration of the instruments was done on a bare soil surface. For lysimetric comparison, one LAS each deployed across two large dryland lysimeter fields (NW and SW) and two large irrigated lysimeter fields (NE and SE) arranged in a block pattern. The refractive index of air was monitored at 1-min interval and averaged at 15-min, and synchronized with weather station and lysimeter measurements. In addition, net radiation (Rn) and soil heat fluxes (G) were measured in all four lysimeter fields. Latent heat fluxes and ET rates were derived using LAS-estimated H as a residual from the energy balance equation. In this presentation, results of cross calibration and lysimetric comparison will be presented and discussed.