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Nguyen, Van-Tho Validation of plant area density estimated from TLS data by using a voxel representation of 3D forests Talk
Van-Tho Nguyen1, Richard A.Fournier1, Jean-François Côté2 and François Pimont3
(1) Department of Applied Geomatics, Centre de Recherche en TELédétection, Université de Sherbrooke, Sherbrooke (QC), Canada(2) Natural Resources Canada, Canadian Forest Service – Canadian Wood Fibre Centre, Quebec (QC), Canada(3) Institut National de Recherche Agronomique (INRA), Avignon, France

Plant Area Density (PAD m2.m-3) defines the total one-sided total plant surface area within a given volume. It is a key variable in characterizing the exchange processes between the atmosphere and the land surface. Terrestrial laser scanning (TLS) provides unprecedented details of the 3D structure of forest canopies. Recent studies made use of statistical estimators of PAD applied on TLS point clouds subdivided into 3D cubes, called voxels. However, a rigorous assessment of the estimated PAD and the impact of occlusions in forests is still unclear due to laborious and inaccurate field measurements. 3D modeling of forests using voxels provides an efficient framework for validating the estimated PAD.

This work presents a validation of the vertical profile of PAD estimated from simulated TLS scan of 3D models of coniferous and hardwood forests. Our method provides unbiased PAD estimates based on voxelization. The results showed strong correlations between vertical profiles of the estimated and reference PAD for virtual forest of coniferous plots with a mean R2 of 0.98. In hardwood plots, we obtained similar correlations for the lower part (mean R2 = 0.97) of the canopy. However, our method underestimated the PAD for the upper part of the canopy due to occlusions, with an average loss of 0.27 m2.m-3 (mean R2 = 0.76). The impact of voxel size on PAD estimations highly depended on the relative size of foliar and woody elements. Thus, hardwood sites characterized with larger foliage units were less sensitive to the voxel size than dense conifer sites.