A multiple‐layer canopy scattering model to simulate shortwave radiation distribution within a homogeneous plant canopy

A multiple‐layer canopy scattering model to estimate shortwave radiation distribution within a wheat canopy was derived mathematically, which incorporated processes of radiation penetration through gaps between leaves, and radiation absorption, reflection, and transmission in leaf layers. The model is able to simulate the multiple scattering processes that occur among different canopy layers and to predict the vertical distributions of upward, downward, and reflected shortwave radiation within the canopy, as well as the magnitude of subcanopy radiation that penetrates to the soil surface. One of the primary advantages of this model, in contrast to other models, is that the multiple scattering processes are represented by a set of linear simultaneous equations that can be solved in a single pass through the equations, without iteration. This achieves computational economy while still accounting for the details of multiple scattering of radiation within the canopy. Stability analyses of the model showed that the canopy, with a leaf area index within a normal field range from 0 to 7, needed to be divided into about 50 or more layers in order to converge upon its final solution. Satisfactory agreement was obtained between model results and field measurements for downward shortwave radiation impinging on the soil surface below the canopy, and upward reflected radiation above the canopy, both for daily total values and for the 20‐min averages throughout the diurnal cycle.