Could plant leaves be treated as Lambertian surfaces in dense crop canopies to estimate light absorption?

Light absorption by plant organs affects the development of a canopy directly through photobiological processes as well as indirectly through its action on organ temperature. Recent radiative models enable light absorption to be estimated for each individual organ within a canopy. These models require parameters describing incident radiation, canopy structure, and optical properties of phytoelements. Among these parameters, the bidirectional optical properties of phytoelements are a stumbling block: they are difficult to measure and take into account efficiently. Thus, most radiative models resort to what is referred to the Lambertian approximation. However, few studies have verified its suitability. In this paper, we assess this approximation in terms of individual leaf absorption for dense crop canopies in the solar spectrum. Simulations were performed with Monte Carlo ray tracing for three canopies, three sun positions, and two spectral domains (photosynthetically active radiation (PAR) and near infrared (NIR)). Results validate the suitability of the Lambertian approximation to simulate the light absorption by plants given the conditions under study.