# Development and Performance Assessment of a Low-Cost UAV Laser Scanner System (LasUAV)
## 3 Results  
The results from angular static and dynamic test activities that allowed calculation of the MAE and standard deviation associated with \(Z\) measurements (\(\sigma_{Z}\)) are reported in Table 3. The MAE and standard deviation of height measured have small differences between angular static and dynamic conditions. Figure 9 illustrates the point cloud from each of the nine passages during the flight. As we can see from Figure 9, the target was reached from laser pulses with different track orientations and laser beam angulations. For example, for P4 and P5, the scan was moderately and largely decentralized, respectively, with respect to the box, and for this reason, the target was hit sideways; for P1, P2, and P7, the scans were slightly decentralized with respect to the target; while for P3, P6, P8, and P9, the box was hit most by laser pulses oriented near-nadir. Figure 10 shows the horizontal positions colored with different tones of the target identified in each of the nine passages. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Acquisition** & **Number of Points** & \(\sigma_{Z}\) **(cm)** & **MAE (cm)** & **RMSE (cm)** \\ \hline S1: Angular static & 150,000 & 3.8 & 3.9 & 5.5 cm \\ S2: Angular dynamic & 600,000 & 3.9 & 3.7 & 5.3 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the uncertainty and accuracy assessment of LiDAR height measurements in angular and static dynamic conditions. The results of the uncertainty analysis in in-flight conditions are reported in Table 4. For each passage, the mean values of scan angle and yaw are reported with the number of returns in the cloud. X and Y are the mean coordinates of the left down edge of the top of the box with respect to the origin of the relative reference system, while Z is the mean ellipsoidal height of the box cover. Figure 10: Horizontal position of the target in each of the nine passages (P1–P9). The origin of the relative coordinate system corresponds to the point (6.2241 \(\times\) 10\({}^{5}\), 4.8576 \(\times\) 10\({}^{6}\)) of the Universal Transverse Mercator (UTM) coordinate system. Figure 9: The target identified from each point cloud of the nine passages. The bar represents the values of the ellipsoidal height, with higher values shown in red. The fuchsia lines represent the UAV flight tracks. In the nine passages, P4 had the worst standard deviation (\(\sigma_{\rm Z}\) = 9.8 cm), which corresponds to the highest value of uncertainty. This is due to the poor results from the differential corrections as a consequence of a weak GNSS signal, which determines the worsening target identification and increased dispersion. This case can be considered an outlier. On the contrary, P8 represents the passage with the lowest uncertainty (\(\sigma_{\rm Z}\) = 5.1 cm). Figure 11 shows the returns that hit the cover of the box in passages P4 and P8. In P4, the cover is positioned at a height higher than expected; this is not interpretable as a bias (understood as a systematic difference between population mean of the measurement results and the accepted reference value), but as uncertainty due to unstable values of the GNSS signal. Figure 12 represents the results from the analysis of possible combinations of passages; the uncertainty in \(Z\) is represented as a function of the number of multiple passages over the target. In the case of a single passage, uncertainty has the lowest value and its standard deviation is the lowest. In the case of nine passages, uncertainty reaches the highest value but its standard deviation is the lowest. This means that there is a trend in the uncertainty of one passage toward nine passages.