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United States Department of Agriculture

Agricultural Research Service

Title: Utility of Radiometric-Aerodynamic Temperature Relations for Heat Flux Estimation

Authors
item Kustas, William
item Anderson, Martha
item Norman, John - UNIVERSITY OF WISCONSIN
item Li, Fuqin

Submitted to: Boundary Layer Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 8, 2006
Publication Date: October 16, 2006
Citation: Kustas, W.P., Anderson, M.C., Norman, J.M., Li, F. 2006. Utility of radiometric-aerodynamic temperature relations for heat flux estimation. Boundary Layer Meteorology. DOI 10.1007/s10546-006-9093.

Interpretive Summary: In many models using remotely sensed land surface temperature observations for estimating soil and vegetation water and energy exchanges, results have not have been generally satisfactory. This is due in part to the non-unique relationship between the so-called aerodynamic temperature, which in model formulations represents the efficiency of heat exchange between the land surface and overlying atmosphere, and a surface temperature measurement from a thermal-infrared radiometer, which largely corresponds to a weighted soil and canopy temperature as a function of radiometer sensor viewing angle. Recent efforts with experimental data have empirically related radiometric-aerodynamic temperature differences to solar radiation and leaf area or the amount of canopy cover. In this study, simulations by a detailed soil-plant-environment model, Cupid, which considers both radiative and turbulent exchanges across the soil-canopy-air interface, are used to explore the radiometric-aerodynamic temperature relations for a semi-arid shrubland ecosystem under a range of leaf area/canopy cover, soil moisture and meteorological conditions. The results indicate that while solar radiation and leaf area both strongly affect the magnitude of the radiometric-aerodynamic temperature differences, the linear relationships are non unique. These simulations show that soil-canopy temperature differences are highly correlated with variations in the radiometric-aerodynamic temperature differences, with the slope being primarily a function of leaf area. The results suggest developing models that can reliably estimate component soil and canopy temperatures and associated resistances are better able to define the radiometric-aerodynamic relation for a range in vegetated canopy cover conditions than are simple, empirically-based schemes.

Technical Abstract: In many land surface models using bulk transfer (one-source) approaches, the application of radiometric surface temperature observations in energy flux computations has given mixed results. This is due in part to the non-unique relationship between the so-called aerodynamic temperature, which relates to the efficiency of heat exchange between the land surface and overlying atmosphere, and a surface temperature measurement from a thermal-infrared radiometer, which largely corresponds to a weighted soil and canopy temperature as a function of radiometer viewing angle. Recent efforts with experimental data have empirically related radiometric-aerodynamic temperature differences to solar radiation and leaf area or canopy cover. In this study, simulations by a detailed soil-plant-environment model, Cupid, which considers both radiative and turbulent exchanges across the soil-canopy-air interface, are used to explore the radiometric-aerodynamic temperature relations for a semi-arid shrubland ecosystem under a range of leaf area/canopy cover, soil moisture and meteorological conditions. The results indicate that while solar radiation and leaf area both strongly affect the magnitude of the radiometric-aerodynamic temperature differences, the linear relationships are non unique, with slopes varying by two orders of magnitude depending on local conditions. These simulations show that soil-canopy temperature differences are highly correlated with variations in the radiometric-aerodynamic temperature differences, with the slope being primarily a function of leaf area. The results suggest that two-source schemes that can reliably estimate component soil and canopy temperatures and associated resistances are better able to define the radiometric-aerodynamic relation for a range in vegetated canopy cover conditions than are simple, empirically-based one-source schemes.

Last Modified: 4/19/2014
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