|Chavez, Jose - Colorado State University|
Submitted to: ASABE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2009
Publication Date: 6/23/2009
Citation: Chavez, J., Gowda, P., Howell, T.A. 2009. Modeling surface aerodynamic temperature in a semiarid advective environment[abstract]. In: Proceedings of the 2009 ASABE Annual International Meeting, June 21-24, 2009, Reno, Nevada. Paper No. 096190.
Interpretive Summary: Crop water use is a major consumptive use of irrigation in agriculture. Numerous energy balance methods were developed for mapping crop water use. However, most energy balance models are complex to use. Efforts are being made to further improve and simplify the models while accurately representing of processes involved. In this study, an attempt is made to improve the estimation accuracy of sensible heat flux. This was done by evaluating a statistical relationship between surface aerodynamic temperature and crop, wind, and temperature parameters. Results indicated that there is a linear relationship exists among these parameters. This relationship can be employed to simplify the calculation of sensible heat flux for estimating crop water use.
Technical Abstract: In mapping evapotranspiration (ET), latent heat flux (LE) can be spatially estimated as an energy balance (EB) residual for land surfaces using remote sensing inputs. The EB equation requires the estimation of net radiation (Rn), soil heat flux (G), and sensible heat flux (H). Rn and G can be estimated with acceptable accuracy. However, H may be under estimated when the radiometric surface temperature (Ts) is used rather than the surface aerodynamic temperature (SAT) in the aerodynamic resistance equation. The overestimation of H may occur because Ts is typically larger than SAT. In computing H, most use Ts instead of SAT as SAT is neither measured nor easily estimated. The objective was to model SAT to improve the estimation of H and consequently ET for the semi-arid, advective environment. A 6-m tower platform was used to measure profiles of wind speed, air temperature, and relative humidity in and above cotton canopy near a large weighing lysimeter managed under dryland conditions in USDA-ARS Conservation and Production Laboratory, Bushland, Texas. The SAT was modeled using H as a residual from the EB at the lysimeter location. Results indicated that SAT was better modeled as a linear function of Ts, air temperature, and surface aerodynamic resistance.