# Monitoring and Data Analysis in Small-Scale Landslide Physical Model
## 3 Review of Landslide Monitoring Equipment
### Geodetic Monitoring System in Small-Scale Landslide Modeling
#### 3.1.1 High-Speed Cameras  
High-speed cameras used for multitemporal landslide analysis from stereo image sequences are part of the ARAMIS system (GOM GmbH, a ZEISS company, Braunschweig, Germany) [53]. ARAMIS is an optical noncontact 3D measuring system by the German company GOM that provides the whole workflow from conducting the measurements, through the analysis of measurement obtained raw data and to the representation of the results. Camera frequency options depend on used sensor or cameras: a single camera system can determine 2D coordinates and measure flat objects, while a stereo pair of cameras system can determine 3D coordinates and measure position of objects in 3D. The software computes coordinates in 3D space and assigns points from the camera images to each other. To be able to compute 3D coordinates, a software needs reference points. Reference points can be point patterns or random patterns which are also called stochastic patterns. Reference point patterns consist of self-adhesive circular points markers with a black background and white center to act as a contrast between black and white color in the software identification along with the orientation of the reference marker points. Random reference patterns can be applied with spray cans or a brush. Over a period of time, the system monitors 3D coordinates. Software then compares coordinates computed during the measuring sequence to derive displacement of the pattern marks to each other [53]. By using the principle of triangulation, software uses computed image point coordinates to compute 3D points on a surface. The point of origin can be calculated if the software recognizes at least two or more signals coming from a point. Software recognizes light by using optical sensors and information from the sensor calibration for the characteristic measured volume and determines spatial coordinates of origin. For the triangulation to be as precise as possible, it is necessary to consider intrinsic or internal camera parameters and extrinsic or external camera parameters. Intrinsic parameters depend on the type of camera used and are internal specifications of the camera, and they are parameters needed to describe the orientation in the image plane. Extrinsic parameters are related to the orientation in space and the position of the camera in the global coordinate system [54].  
The ARAMIS system sensors enable real-time measurement for a large number of points on the surface of an observed object. The system is adjustable, meaning it can measure a wide range of volumes--from samples of a few square millimeters to few square meters. The flexibility of sensor use due to the variable measuring volumes and distances facilitates variety of measuring tasks. Optical measuring system consists of a sensor with two cameras (3D setup), cables, stand, calibration object, pair of lenses, laser pointer for optimum sensor adjustment, LED lights, and a photocell.  
The series of tests was recorded by the above-described set of two 4-megapixel cameras. In the later stages of the project, another set of cameras was obtained. This system works on the same principle but with a few improvements--two 12-megapixel cameras with high spatial resolution and a pixel size of 3.45 \(\upmu\)m [55]. In Figure 3, both sets of cameras are shown, while in Table 4, characteristics of both camera systems are stated for comparison.  
The first image sequence made of the measuring object presents the initial state of the object before the test. Before the beginning of the test, an initial calibration dependent of the measuring volume must be conducted. For the small-scale landslide physical model, a calibration cross (2 m dimensions) for bigger volumes was used. ARAMIS system was not used before in similar research to observe surface displacements in a landslide body, but it was used and checked in several different dynamic experiments in observation of surface point displacement and velocity measurements [56; 57].