J. A. Smith

D. S. Kimes

K. J. Ranson

A thermal canopy signature model (TCSM) was developed to approximate the thermal behavior of a vegetation canopy by a mathematical abstraction of three horizontal layers of vegetation. Canopy geometry within each layer is quantitatively described by the foliage and branch orientation distributions. Canopy geometry, solar irradiance, air temperature, horizontal wind velocity, relative humidity, and ground temperature are used to calculate the energy budgets of average leaves within each layer. The resulting system of conservation equations is solved for the average layer temperature. This information, together with the angular distributions of radiating elements, is then used to calculate the thermal exitance as a function of view angle above the canopy. Optical diffraction techniques were developed and employed to measure canopy geometry. Solar radiation absorption with the vegetation terrain elements is calculated using a modification of a Monte Carlo model (SRVC) developed for the reflective energy regime. The models were applied to a lodgepole pine (Pinus contorta) canopy and the results for a diurnal cycle are validated with radiometric measurements. Simulated versus measured radiometric average temperatures of Layer 2 correspond approximately within two degrees centigrade. Simulated results suggest that canopy geometry can significantly influence the effective radiant temperature recorded by a sensor above the canopy as a function of view angle. (Author).

D. S. Kimes

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