Operational assessment of aboveground tree volume and biomass by terrestrial laser scanning

The assessment of aboveground tree biomass (AGB) is essential to the evaluation of tree populations in forests, open landscapes, and urban areas. The predominant method used to determine AGB relies on error-prone functions derived from the statistical relationships of tree attributes and biomass. Terrestrial laser scanning (TLS) offers a new approach that replaces statistical AGB estimates with consistent measurements. Aboveground tree biomass (AGB) comprises stems and branches. While the biomass assessment of stems is straightforward, TLS measurements of tree crowns are far more complex because of branch overlapping. Because placing reflecting targets in the crowns of tall standing trees is impractical, yet necessary for merging the point clouds from different laser scan positions, TLS measurements often fail in operational applications. This study introduces a straightforward algorithm that simplifies biomass measurements of complex branch geometries using TLS and derives AGB by averaging measurements from individual scanning positions. We verified our approach through an experimental setup of branching systems with different complexities and known true biomass volumes. The results show that biomass extraction from branches by TLS systems is not affected by scanning distance. The combination of biomass measurements from individual scanning positions by averaging provides reliable biomass figures. Compared to the known true biomass figures, the overall accuracies achieved by our approach are 95 or higher, which brings the operational application of TLS for AGB measurements within tangible reach