Wednesday, November 15, 2006

Evaluation of the Shaw Model for Within-Canopy Radiation Exchange.

Gerald N. Flerchinger1, Wei Xiao2, Tom J. Sauer3, and Qiang Yu2. (1) USDA Agricultural Research Service, 800 Park Blvd., Suite 105, Boise, ID 83712, (2) Institute of Geographical Sciences and Natural Resources Research, Graduate School of the Chinese Academy of Sciences, No. 11A Datun Road, Beijing, 100101, China, (3) USDA-ARS National Soil Tilth Lab, 2150 Pammel Dr, Ames, IA 50011

Radiation exchange at the surface plays a critical role in the surface energy balance, plant microclimate, and plant growth. The ability to simulate the surface energy balance and the microclimate within the plant canopy is contingent upon accurate simulation of the surface radiation exchange. A validation and modification exercise was conducted of the Simultaneous Heat and Water (SHAW) model for simulating the surface radiation exchange over and within wheat, maize and soybean plant canopies. Although the original SHAW model slightly underpredicted reflected solar radiation, one would conclude that the simulations were quite reasonable if within-canopy measurements were not available. However, within canopy radiation was seriously underestimated by the original SHAW model. Improvements were made to the SHAW model for simulating radiation exchange within the plant canopy.  Modification to the SHAW model improved both above canopy reflected radiation and within-canopy radiation simulations for wheat, maize and soybean canopies.