Modeling maize canopy 3D architecture: Application to reflectance simulation

The aim of this study is to develop a 3D model of maize ( Zea mays) canopy structure for accurate reflectance simulations. We focus on fully developed maize plants without paying attention to the reproductive organs. Several experiments are used to describe the dimension, shape, position and orientation of the leaves and stems. They correspond to a wide range of cultural practices. Empirical models are proposed to derive the position, size, and shape of the leaves and stems as a function of three main variables: the final number of leaves, the final height of the canopy and the cumulated leaf area per plant that is considered as a vigor index. Leaf orientation is described through the curvature of the main rib and the cross section used to represent the undulation of the lamina. The statistical distributions of the parameters of each structure sub-models are investigated. It allows to generate realistic computerized plant and canopy 3D architecture representation. The canopy structure is then used to compare the SAIL reflectance model to the reflectance simulated with PARCINOPY which is a monte-carlo ray tracing model. The combined use of detailed canopy architecture models and quasi exact radiative transfer models such as PARCINOPY appears to be a very convenient tool to evaluate more simple reflectance models applied to specific vegetation types. Results show a general good agreement between the two models, except for the exponential hot-spot function used in the SAIL model, and the directionality of the multiple scattering.