# Monitoring and Data Analysis in Small-Scale Landslide Physical Model
## 4 Results
### High-Speed Cameras  
The results of high-speed camera measurements are 3D coordinates captured in time and derived calculated values such as displacements, strains, velocities, and accelerations at individual points on a landslide surface caused by static or dynamic loads. The principle of measurement is based on digital image correlation and successfully replaces a large number of traditional measuring devices (e.g., LVDTs, strain gauges, extensometers, and accelerometers). A small-scale physical model of landslide constructed in the laboratory was observed by a pair of high-speed cameras to obtain stereo pair image sequences (Figure 7a,b) used for multitemporal landslide analysis. The duration and changes in filming frequency during the tests conduction are listed in Table 9. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Slope Angle (\({}^{\circ}\))** & **Rainfall Intensity (mm/h)** & **Initiation Time (min)** \\ \hline Test 1 & 30 & 58/122 & 126 \\ Test 2 & 35 & 73 & 62 \\ Test 3 & 45 & 73/63 & 75 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Test conditions and landslide initiation times. In the following text, the results obtained in the Test 2 are described together with an analysis of the surface displacement. The whole Test 2 was recorded in 479 image sequences according to the filming duration of 2 h 11 min 10 s. As there is almost no change in displacement in the beginning of the test, recording speed was adjusted in several stages of the recording, becoming increasingly dense at the end of the test when most of the displacements happened. Reference points used on the physical model were circular white pins dyed with black marker; therefore, the reference is based on the contrast of black and white. Pins are arranged in the regular mesh at the distances of 20 \(\times\) 10 cm, in 5 rows and 24 columns from the camera view, with total number of 120 reference pins. The analysis along the middle longitudinal profile of the slope model is presented here. The next few figures show the process of analysis of displacements and deformations of the surface of the physical model along the profile. Because of a large number of the recorded image sequences, there are too many graphical stages to be presented, which is a reason why only points along one profile are analyzed and shown. Point markers are named by their position: the first number in the name represents the row, and the second number represents the column of the marked point, as is shown in Figure 8. To be able to track a point through the recording, the point must be visible at all stages in both cameras. Every point marker within the field of view is assigned values of \(x,y,\) and \(z\) coordinates based on the recognized reference point. Certain points are not assigned because they are not visible in both sets of images (e.g., the first column at the bottom of the model was not considered because the left camera did not encompass that part of the landslide model). Additionally, some points could not  
Figure 7: Landslide physical model recorded by a high-speed camera: (**a**) left camera; (**b**) right camera. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No.** & **Part** & **Filming Frequency (fps)** & **dt (s)** & **Duration** & **No. of Stages** & **Mesh of Pins** \\ \hline \multirow{4}{*}{Test 1} & 1 & 1/300 & 300 & 1 h 1 min 37 s & 12 & \\  & 2 & 1/60 & 60 & 1 h 12 min 45 s & 72 & \\  & 3 & 1/10 & 10 & 1 h 37 min 2 s & 582 & 4 \(\times\) 14, distanced 20 \(\times\) 20 cm \\  & & & & Total & 666 & \\ \hline \multirow{4}{*}{Test 2} & 1 & 1/300 & 300 & 52 min 59 s & 10 & \\  & 2 & 1/10 & 10 & 1 h 18 min 11 s & 469 & 5 \(\times\) 24, distanced 20 \(\times\) 10 cm \\  & & & & Total & 479 & \\ \hline \multirow{4}{*}{Test 3} & 1 & 1/300 & 300 & 37 min 59 s & 7 & \\  & 2 & 1/60 & 60 & 30 min 35 s & 30 & \\ \cline{1-1}  & 3 & 1 & 1 h 15 min 4 s & 4504 & 5 \(\times\) 12, distanced 20 \(\times\) 20 cm \\ \cline{1-1}  & & & & Total & 4541 & \\ \hline \hline \end{tabular}
\end{table}