Radiative models for architectural modeling

Light microclimate determines many aspects of plant growth. Introducing the light-vegetation interactions into a plant model requires a radiative model computing fluxes at the spatial scale described in the plant model. The three-dimensional (3D) architectural models describe plants functionally and geometrically as sets of interconnected organs. As the geometry of each organ is defined, the 3D canopy structure is explicitly described. These models require calculation of the distribution of light energy on the 3D plant structure, to integrate physiological processes from organ to plant level. This has motivated the development of new radiative models. We introduce first the principles governing the physical interactions between light and a plant canopy. We present then operational models. Fast methods have been developed for calculating sun and sky light directly intercepted by plant organs. Such methods may be used for the simulation of processes depending on the UV or PAR radiations. Models taking into account the multiple scattering between plant elements are based either on Monte Carlo ray tracing or on the radiosity method. We present the principle of these approaches and recent developments on their applications to crop modelling. ((C) Inra/Elsevier, Paris.).