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United States Department of Agriculture

Agricultural Research Service

Research Project: SUSTAINING RURAL ECONOMIES THROUGH NEW WATER MANAGEMENT TECHNOLOGIES

Location: Soil and Water Management Research

Title: Effect of scintillometer height on structure parameter of the refractive index of air measurements

Authors
item Gowda, Prasanna
item Howell, Terry
item Hartogenis, Oscar -
item Basu, Sukanta -
item Scanlon, Bridget -

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: November 10, 2009
Publication Date: December 15, 2009
Citation: Gowda, P., Howell, T.A., Hartogenis, O., Basu, S., Scanlon, B. 2009. Effect of scintillometer height on structure parameter of the refractive index of air measurements [abstract]. American Geophysical Union Meeting, December 13-17, 2010, San Francisco, California. Paper No. H43J-06.

Technical Abstract: Scintillometers measure amount of scintillations by emitting a beam of light over a horizontal path and expresses as the atmospheric turbulence structure parameter as the refractive index of air (Cn**2). Cn**2 represents the turbulent strength of the atmosphere and describes the ability of the atmosphere to transport heat and humidity. The main objective of this study was to evaluate the effect of scintillometer height on Cn**2 measurements and on the estimation of latent heat fluxes. The study was conducted during the 2009 summer growing season in the USDA-ARS Conservation and Production Research Laboratory (CPRL) at Bushland [35 degrees 11' N, 102 degrees 06' W; 1,170 m elevation MSL], Texas. Field experiment consisted of two steps: (1) cross-calibration of scintillometers and (2) measurement of Cn2 at different heights. In the first step, three large aperture scintillometers (LAS) were deployed across two large lysimeter fields with bare soil surfaces. During the 3-week cross-calibration period, all three scintillometers were installed at a 2-m height with a path length of 420 m. Cn**2 was monitored at a 1-min interval and averaged for 15-min periods. Cn**2 measurements were synchronized with weather station and weighing lysimeter measurements. After the cross-calibration period, scintillometers were installed at 2-, 2.5- and 3-m heights, and Cn**2 measurements were continued for another 3-week period. In addition to the Cn**2 measurements, net radiation (Rn) and soil heat fluxes (G) were measured in both lysimeter fields. Cn**2 values were corrected for inner scale dependence before cross calibration and estimation of sensible heat fluxes. Measurements of wind speed, air temperature, and relative humidity were used with Cn**2 data to derive sensible heat fluxes. Latent heat fluxes were estimated as a residual from the energy balance and compared with lysimeter data. Results of cross calibration and effects of scintillometer height on the estimation of latent heat fluxes were reported and discussed.

Last Modified: 8/31/2014
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