# Comparison and Combination of Mobile and Terrestrial Laser Scanning for Natural Forest Inventories
## 5 Results
### Quantitative Structure Models  
QSMs were generated for all 24 trees of plot 1 and all 22 trees of plot 2 of the TLS and MLS leaf-off datasets. For two trees of plot 1, illustrated in Figure 6, the results are exemplified in more detail. The first one is a _Carpinus betulus_ tree with a height of 18 m and a DBH of 17.5 cm. The tree is positioned 26.3 m from the forest path. The second one is a _Fagus sylvatica_ tree with a height of 32 m and a DBH of 52.7 cm. This tree is placed 7.5 m away from the forest path. Despite the low number of points of the MLS segmented trees compared to the TLS trees (max. 14% of the achieved TLS points), the derived values such as tree height, CPA and DBH show on average only small deviations from the TLS estimated parameters (Table 4). A detailed list (Tables A3 and A4) of the QSM parameters for plot 1 and 2 can be found in Appendix C. The obtained QSMs of the two trees from plot 1 are shown in Figures 9, A3 and A4 in Appendix D. Due to the proportion of the point number, the point clouds in Figure 9c,d look almost the same (0.122), while the point clouds of Figure 9a,b show a clear difference (0.047). The QSMs were generated up to the 5 th order branches. The CPA is shown in Figure 10 with a RMSE of 2.9 m\({}^{2}\) (plot 1) and 2.2 m\({}^{2}\) (plot 2). It becomes obvious that the MLS extracted CPAs fit well but are slightly underestimated. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Plot 1** & **Point Number** & **Tree Height** & **Total Volume** & **CPA** \\ \hline _Carpinus betulus_ & 0.047 & 0.953 & 0.553 & 0.862 \\ _Fagus sylvatica_ & 0.122 & 0.997 & 0.72 & 0.967 \\ Min & 0.008 & 0.894 & 0.336 & 0.815 \\ Max & 0.143 & 0.997 & 1.273 & 1.025 \\ Mean value & 0.055 & 0.972 & 0.745 & 0.938 \\ \(\sigma_{0}\) & 0.035 & 0.022 & 0.210 & 0.051 \\ \hline
**Plot 2** & **Point Number** & **Tree Height** & **Total Volume** & **CPA** \\ \hline Min & 0.033 & 0.933 & 0.303 & 0.875 \\ Max & 0.197 & 0.997 & 0.850 & 0.985 \\ Mean value & 0.096 & 0.974 & 0.463 & 0.946 \\ \(\sigma_{0}\) & 0.043 & 0.015 & 0.127 & 0.033 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of the proportion \(x_{MLS}/x_{TLS}\) of the parameters derived from the QSM of 24 trees of plot 1 and 22 trees of plot 2 determined with TLS and MLS. The two trees from Figure 6 are marked with a green (_Carpinus betulus_) and red (_Fagus sylvatica_) color. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Tree** & **DBH Cylinder Fit** & **DBH Cylinder Fit** \\  & **Plot 1** & **Plot 2** \\ \hline _Carpinus betulus_ & 0.922 & - \\ _Fagus sylvatica_ & 0.957 & - \\ Min & 0.741 & 0.741 \\ Max & 1.243 & 1.150 \\ Mean value & 0.961 & 0.906 \\ \(\sigma_{0}\) & 0.108 & 0.115 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of the proportion \(DBH_{MLS}/DBH_{TLS}\) of the DBH derived from the QSM of 24 trees (plot 1) and 22 trees (plot 2) determined with TLS and MLS. The two trees from Figure 6 are marked with a green (_Carpinus betulus_) and red (_Fagus sylvatica_) color. Figure 10: Crown projection area captured from the segmented trees. Figure 9: Segmented tree point clouds with the extracted QSM of two trees of the leaf-off datasets of plot 1. Top: _Carpinus betulus_ tree (**a**) TLS; (**b**) MLS; Bottom: _Fagus sylatica_ tree (**c**) TLS; (**d**) MLS. Figure 11a depicts the proportion of the MLS data points to the TLS data points of each segmented tree. The proportion of the number of branches of the MLS to TLS generated by the QSM is shown in Figure 11b. All branches modeled were taken into account. A maximum of 18% (plot 1) and 29% (plot 2) of the branches were modeled from the MLS data compared to the TLS data, which will be reflected in the volume determination. From this analysis it is confirmed that the number of points and the number of extracted branches decreases with increasing distance of a tree from the trajectory.