article · European Journal of Forest Research
Quantitative structural models convert terrestrial laser scanning point clouds into geometric shapes to measure tree volume and structure. While these models are widely applied to measure whole trees, their reliability at branch level remains uncertain. An evaluation of ten European beech branches scanned at distances between 5 and 45 metres reveals major limitations. As distance from the scanner increases, point cloud density drops and reconstructed branch length declines significantly. Conversely, branch volume estimates rise substantially. At a distance of 45 metres, cumulative branch length was underestimated by an average of 75 percent, whilst individual branch volume was overestimated by up to 539 percent, depending on modelling hyperparameters. These errors stem from reduced point cloud quality at greater distances, where larger laser footprints and wider point spacing prevent accurate capture of smaller branch structures.
Terrestrial laser scanning is increasingly relied upon for non-destructive forest measurements, carbon accounting, and ecological research. However, substantial overestimations of branch volume at standard field scanning distances show that data can be misleading. Recognising these geometric errors helps foresters and researchers avoid severe inaccuracies when modelling tree architecture, biomass, and forest canopies from remote point clouds.
This research provides essential calibration benchmarks for developers of forest measurement software, remote sensing practitioners, and forestry inventory services. By defining operational distance limits, the findings can guide the design of scanning protocols and error-correction algorithms for commercial forest inventory tools. The findings represent applied methodological testing, requiring integration into existing quantitative structural modelling software before direct commercial deployment.
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Abstract Quantitative structural models (QSMs) are frequently used to simplify single tree point clouds obtained by terrestrial laser scanning (TLS). QSMs use geometric primitives to derive topological and volumetric information about trees. Previous studies have shown a high agreement between TLS and QSM total volume estimates alongside field measured data for whole trees. Although already broadly applied, the uncertainties of the combination of TLS and QSM modelling are still largely unexplored. In our study, we investigated the effect of scanning distance on length and volume estimates of branches when deriving QSMs from TLS data. We scanned ten European beech ( Fagus sylvatica L.) branches with an average length of 2.6 m. The branches were scanned from distances ranging from 5 to 45 m at step intervals of 5 m from three scan positions each. Twelve close-range scans were performed as a benchmark. For each distance and branch, QSMs were derived. We found that with increasing distance, the point cloud density and the cumulative length of the reconstructed branches decreased, whereas individual volumes increased. Dependent on the QSM hyperparameters, at a scanning distance of 45 m, cumulative branch length was on average underestimated by − 75%, while branch volume was overestimated by up to + 539%. We assume that the high deviations are related to point cloud quality. As the scanning distance increases, the size of the individual laser footprints and the distances between them increase, making it more difficult to fully capture small branches and to adjust suitable QSMs.
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DOI: 10.1007/s10342-023-01651-z
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