Radiative transfer sensitivity to the accuracy of canopy structure description. The case of a maize canopy.

摘要

Ray tracing techniques make possible very accurate computations of radiative transfer in complex canopy architecture, but their use is limited by the large computer resources required which increase with the number of triangles used to approximate the actual canopy structure. An investigation was made of the sensitivity of the gap fraction, the leaf inclination distribution function and the bi-directional reflectance, to the detail with which canopy architecture was represented, using a maize canopy described using a realistic 3D architecture model. It was shown that 24 plants made it possible to obtain an accurate representation of the gap fraction and the leaf angle distribution function with the finest triangulation level studied (maximum length of longest side of the triangles <0.025 m). The canopy architecture was then degraded by non-representation of leaf undulation. Results showed that under the conditions studied, leaf undulation induced only marginal variation in the gap fraction, the leaf inclination distribution function and the bi-directional reflectance. The canopy architecture was then degraded by dividing by a factor of 10 the number of triangles used in the previous representation. Here again, results showed marginal effects onthe variables investigated.