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

Ray tracing techniques can be very accurate for radiative transfer computation in complex canopy architecture. However, they are limited by the large computer resources required which increase with the number of triangles used to approximate the actual canopy structure. The objective of this study was to investigate 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. We considered a maize canopy described using a realistic 3D architecture model. We showed that 24 plants allowed us to obtain an accurate representation of the gap fraction and the leaf angle distribution function with the finest triangulation level studied, i.e. with triangles smaller than 0.025 m. We then degraded the canopy architecture by non-representing leaf undulation. Results showed that in our conditions, leaf undulation induced only marginal variation of the gap fraction, the leaf inclination distribution function and the bi-directional reflectance. We then finally degraded canopy architecture by dividing by a factor of 10 the number of triangles used in the previous representation. Here again, results showed marginal effects on the variables investigated. Conclusions are drawn and discussed in view of radiative transfer computation. ((C) Inra/Elsevier, Paris.).