U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version



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


U.S. government work.


Radiometric surface temperature (Ts) is commonly used as a surrogate for aerodynamic temperature (To) 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 (zor) or some related form (e.g., kBr -1 = ln[zom/zor], where zom is the momentum roughness length). In this paper, we estimated To – Ta (where Ta is air temperature at 2 m height) and zor using large, precision weighing lysimeters planted with irrigated alfalfa, irrigated and dryland cotton, and dryland grain sorghum. Ts was measured by infrared thermometers mounted over the lysimeters. No apparent relations were found between (To – Ta) and (Ts - Ta) or between zor (in the kBr -1 form) and meteorological variables or leaf area index (LAI). The kBr -1 parameter appeared to be most influenced by the different surface roughness of each crop type. Using constant kBr -1 values established for each type of surface, the energy balance model showed reasonable agreement with H and LE derived from lysimeter measurements.