This thesis presents a new method, Real Twig, to correct volume overestimation in small branches and twigs in quantitative structure models (QSM). Twigs are the smallest above-ground woody structure on a tree and contain delicate tissues used in growing new woody material, leaves for photosynthesis, and fruits for reproduction. Remote sensing with terrestrial laser scanning (TLS) can capture the unique branching structure of trees with millions of indirect measurements stored as a three-dimensional point cloud. QSMs are cylinder models fit to tree point clouds that define a tree’s branching structure as a topological network of cylinders, providing non-destructive estimates of total tree volume and surface area. However, TLS cannot accurately resolve fine details in a tree, specifically twigs, due to physical limitations of TLS sensors, causing the twigs to be much larger in the point cloud than they are in the actual tree. Since QSMs are built from point clouds, the twigs represent a large source of whole-tree volume overestimation directly proportional to the total twig volume in the tree, with error often double the tree’s actual volume, even with the current best correction methods applied. The thesis results show the Real Twig method drastically outperforms all the current best correction methods, by combining direct twig diameter measurements with dynamic taper models to produce visually realistic QSMs that overcome deficiencies in TLS sensor technology. The results show a drastic reduction in QSM volume overestimation, with total tree volume consistently within ± 10% of the real tree. The results also show that TLS data collection must be optimized around the species-specific twig diameter measurement. Finally, a detailed description of the method, a novel database of twig diameter measurements, and tools for QSM visualization, manipulation, and the calculation of QSM-based tree metrics, can be found in an open source R package called rTwig.
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