Comparison of aerodynamic and radiometric surface temperature using precision weighing lysimeters

Authors

Paul D. Colaizzi, USDA-ARSFollow
Steven R. Evett, USDA-ARSFollow
Terry A. Howell, USDA-ARSFollow
Judy A. Tolk, USDA-ARS

Date of this Version

2004

Citation

Remote Sensing and Modeling of Ecosystems for Sustainability edited by Wei Gao, David R. Shaw, Proceedings of SPIE Vol. 5544 (SPIE, Bellingham, WA, 2004). 0277-786X/04/$15. doi: 10.1117/12.559503

Comments

U.S. government work.

Abstract

Radiometric surface temperature (T_s) is commonly used as a surrogate for aerodynamic temperature (T_o) in computing the sensible heat flux term (H) in the energy balance. However, these temperatures may differ by several degrees, leading to possible errors (especially for large H) and their relationship is not well known. Previous researchers have established empirical and semi-empirical parameterizations of the radiometric roughness length (z_or) or some related form (e.g., kB_r ^-1 = ln[z_om/z_or], where z_om is the momentum roughness length). In this paper, we estimated T_o – T_a (where T_a is air temperature at 2 m height) and z_or using large, precision weighing lysimeters planted with irrigated alfalfa, irrigated and dryland cotton, and dryland grain sorghum. T_s was measured by infrared thermometers mounted over the lysimeters. No apparent relations were found between (T_o – T_a) and (T_s - T_a) or between z_or (in the kB_r ^-1 form) and meteorological variables or leaf area index (LAI). The kB_r ^-1 parameter appeared to be most influenced by the different surface roughness of each crop type. Using constant kB_r ^-1 values established for each type of surface, the energy balance model showed reasonable agreement with H and LE derived from lysimeter measurements.