Three dimensional model of the interception of light by a canopy

We present a computer model that simulates, in three dimensions, the interception of light by a canopy. The model divides the canopy into cubic cells, each one characterized by mean leaf angle and the leaf area index. The model calculates the probability that a beam will penetrate to any given cell without being intercepted by the foliage in the path, using an exponential extinction function. Penetration of direct and diffuse light is calculated separately. The model also considers the reflection and transmission of light. The model has been tested against real measurements taken in an artificial plantation, reaching an r(2) of 0.714 between predicted and observed values. A sensitivity test of the model is also presented. The parameters analyzed are: total Leaf Area Index (LAI), vertical distribution of LAI, incident radiation, mean angle of leaves, transmission coefficient of leaves and elevation of the sun. A stepwise regression analysis of the results let us identify the variables which most affect the model outputs: Leaf Area Index, elevation of the sun, mean leaf angle, and incident radiation. The transmission coefficient of leaves does not exert significant influence on the intercepted radiation. The proportions of direct and diffuse components in incoming radiation have a significant influence on the results. (C) 1998 Elsevier Science B.V.