# Mobile LiDAR for Scalable Monitoring of Mechanically Stabilized Earth Walls with Smooth Panels
## 5 Experimental Results
### Comparative Analysis of TLS and MLS Serviceability Measures
To evaluate the accuracy of the automatically-derived panel-to-panel normal displacement between adjoining panels, such distances have been compared to interactive measurement of the displacement in the TLS point cloud, MLS point cloud, and on-site profiler gauge measurements derived at locations \(i\), \(ii\), and \(iii\)--refer to Figure 21. The individual checks of the panel-to-panel normal displacement are shown in Figure 22--where Figure 22a shows the manual measurements from the point cloud and Figure 22b shows the on-site profiler gauge measurements. In this regard, one should note that the on-site profiler gauge measurements are an independent evaluation of the absolute accuracy of derived normal distances. The estimated values for panel-to-panel normal displacements from the above approaches are shown in Figure 23. The results in Figure 23 indicate that the panel-to-panel normal displacements from the TLS and MLS data as evaluated by automated approach or interactive measurement of the displacement in the LiDAR point cloud as well as the on-site profiler gauge measurements were in good agreement (i.e., the reported numbers in Figure 23 are within the range of \(\pm\)0.5 cm). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**New-Available Serviceability Measures**} & \multicolumn{3}{c}{**Standard Serviceability Measures**} & **Quality Control** \\ \hline  & \(X_{o}\)** **(m)** & \(Y_{o}\)** **(m)** & \(Z_{o}\)** **(m)** & \(\theta_{up}\)** **(deg.)** & \(\theta_{up}\)** **(deg.)** & \(\theta_{up}\)** **(deg.)** & \(\alpha_{L}\)** **(10\({}^{-3}\))** & \(\alpha_{T}\)** **(10\({}^{-3}\))** & **Panel-to-Panel Disp. (m)** & **W (m)** & **H (m)** \\ \hline RMSE & 0.001 & 0.0027 & 0.019 & 0.23 & 0.30 & 0.048 & 0.34 & 0.37 & 0.0039 & 0.010 & 0.022 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: RMSE of evaluated differences between TLS and MLS-based serviceability measures for a total of 76 complete panels covering faces 2, 3, and 4 along facade 2 for the MSE wall. Figure 21: Overall out-of-plane displacement map for a face along the MSE wall facade (reported values along the scale bar are in meters) and locations (\(i\), \(ii\), and \(iii\)) for validating the automatically-derived displacement. Figure 23: Validation of panel-to-panel out of-plane displacement (different colors in the interactive point cloud measurements columns represent different panels). Figure 22: Validation of panel-to-panel normal distance measurement: (**a**) interactive measurement from point cloud and, (**b**) on-site profiler gauge approach. Now that we evaluated the comparative performance of TLS and MLS in reporting global and local serviceability measures, one can proceed with evaluating the measures for the MSE wall that has been surveyed by the MLS. Regarding the whole MLS dataset, Table 5 provides summary statistics of the proposed serviceability measures, derived using the MLS point clouds from different drive runs, for the complete and non-occluded panels of the smooth MSE wall (160 panels in total). Figure 24 shows the CDFs for the three angular values (\(\theta_{xp}\), \(\theta_{yp}\), and \(\theta_{zp}\)) and panel-to-panel normal distance of the MLS dataset in this case study site. The graphical summary in Figure 24 is much easier to use for identifying trends and outliers than examining the values of each individual panel of the MSE wall. As can be seen in Table 5, the angular deviation values were less than 1\({}^{\circ}\) for the tilts around the \(x\)-, \(y\)- and \(z\)-axes. Table 5 also shows that 95% of the panels had an offset less than 1.00 cm, which indicates that the MSE wall meets the acceptable out-of-plane offset recommended by FHWA [7].