HR: 0800h
AN: H41A-0399    [Abstracts]
TI: Modeling of Long Wave and Net Radiation Energy Distribution Within a Homogeneous Vegetation Canopy via Multiple Scattering Processes
AU: * Zhao, W
EM: wzhao@uidaho.edu
AF: University of Idaho, Dept. Biological and Agricultural Engineering POB 440904, Moscow, ID 83844-0904 United States
AU: Qualls, R J
EM: rqualls@uidaho.edu
AF: University of Idaho, Dept. Biological and Agricultural Engineering POB 440904, Moscow, ID 83844-0904 United States
AB: This paper presents a newly developed multiple-layer, long wave radiation scattering model for use in homogeneous vegetation canopies. The model is able to simulate the long wave radiation distribution within the canopy as well as the outgoing long wave radiation above the canopy. This model differs from the shortwave model developed earlier by the authors owing to the complexity introduced by the fact that leaves and soil in and below the canopy emit long wave radiation in accordance with their surface temperature. Combined with the short wave radiation scattering model, the pair of models is able to simulate net radiation distribution above and within the canopy sublayers as well as at the soil surface. The model represents multiple scatterings of radiation reflected, transmitted and emitted from leaf surfaces, and penetrating through gaps, as infinite series equations, which are reduced analytically to simple forms. In order to validate the model, field measurements in a wheat field near Moscow, Idaho, USA were collected during the growing season from May 29 to August 11, 2002. Measurements included the four components of the incoming and outgoing short- and long-wave radiation, net radiation, leaf area index, crop height, and canopy temperature profile. Satisfactory agreement was obtained between the modeled outgoing long wave radiation above a wheat canopy and observed long wave radiation measured with a PIR radiometer, both for daily total values and diurnal variation of 20-minute averages. The Root Mean Squared Error (RMSE) of daily total values of outgoing longwave radiation, with respect to measurements, was within 1.1% of the mean of the measurements. Comparison of the modeled net radiation above a wheat canopy with two independent measurements, one from a net radiometer, and the other based on measurements of the four separate radiation components, showed good agreement, both for the daily total values and diurnal variations on both clear days and a cloudy day. For daily total net radiation, RMSE was within 3.7% and 5.0% of the measured daily total for clear and cloudy days, respectively.
DE: 0466 Modeling
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1814 Energy budgets
DE: 1878 Water/energy interactions (0495)
DE: 3322 Land/atmosphere interactions (1218, 1631, 1843)
SC: Hydrology [H]
MN: Fall Meeting 2005