## 2 Related Work  
Mobile mapping systems are becoming popular as they can build 3D point clouds of any type of environment rapidly by using a laser scanner that is integrated with a navigation system. The laser scanner is able to record millions of points. The files with the point clouds can be viewed, navigated, measured and analyzed as discrete 3D models. The evolution of the laser scanner as a surveying technique has resulted in this tool being used not only to obtain an optimal geometric reconstruction of the scene, but also to assess changes in a particular state. Mobile LiDAR (Light Detection And Ranging) technology presents some advantages: high-speed data capture through reduction of time and cost, remote acquisition and measurement increasing survey in efficiency and safety, high point density data ensuring a comprehensive representation of the detected scene, an abundance of data acquired in movement. The light weight of these MLSs makes them flexible and versatile instruments, so they can be mounted on any mobile platform. In places with complex topography, the use of MMS, following a continuous path, is more advantageous than a tripod-based laser scanner that requires multiple scan positions to cover all the areas of the survey [6]. Moreover, integrating MMS with other geomatics techniques, such as Digital Photogrammetry (DP), allows giving an added value and greater richness of the acquired data providing a high detailed DEM or DTM (Digital Terrain Model) of the selected area [8]. Alternative purposes to use mobile LiDAR technologies, in addition to the assessment of the geometrical state, concern change detection, deformation analysis [9], hazard assessment and structural and infrastructural health monitoring [4] in different types of natural environment. In technical terms, mobile mapping solutions contemporaneously allow users to acquire geometrical aspects for geological studies and geomorphological analysis, to operate mapping of all the elements present in the detected area (e.g., vegetation, road, etc. ), and to define basic modeling for monitoring operations (e.g., rockfalls, coastal erosion, river dynamics, etc.). Examples described by literature are various, depending on natural effects as geological and atmospheric actions or anthropogenic consequences of the built environment which compromise the stability of the natural landscape. The major case studies that include the use of MLS for mapping and monitoring purposes are those related to geomorphology detection and landscape dynamics such as landslides and rockfall displacements. The combination of MLS and DP can greatly improve the realization of detailed modeling of the geometrical discontinuity of a slope to analyze a landslide susceptibility and potential rockfall mechanisms [9]. Examples of slope stability assessment through the kinematic method are applied in rock outcrops in British Columbia, Canada, and Carrara marble quarry, Italy [10]. The use of MLS was presented by [PERSON] et al. [11] in a geological study of landslides applied to an interesting case study in Normandy. They used a boat-based MMS to scan 3D point clouds of unstable coastal cliffs to detect rockfalls and erosional deposits. A similar case is proposed by [12] who described a new approach of coastal cliff monitoring, in Poland, which is based on a combination of MLS from the sea with the geotechnical stability calculations. A 3D mapping was carried out by an airborne MMS, installed on a helicopter, to monitor a small landslide in the North Yorkshire coast in the UK. As a result, more accurate modeling of the terrain was obtained, especially areas covered by vegetation [13]. A ground-based approach was evaluated by [PERSON] et al. [5] using a handheld MLS to collect topographic data in complex terrain as a gully site at the coastal cliff in Sunderland, UK. To carry out the survey, the hand-held mobile device is walked around the site following a close loop path to facilitate accurate 3D reconstruction and avoiding problems associated with drift.