Terrain slope analyses between terrestrial laser scanner and airborne laser scanning

Landslide is a geohazard phenomenon of mass movement of terrain. In order to prevent landslide, understanding the behavior of the landslide is of importance. In such a case, many landslide monitoring rely on accurate digital terrain models (DTM). Typically, DTM can be generated by point based measurements such as GPS, leveling, total station and laser distancemeters. However, these methods will raise obvious measurement problems because of the discontinuous character since they only allow measuring discrete points, and therefore it can be difficult to ensure that problems are recorded and handled in a consistent manner. In recent years, the `Light Detection and Ranging - LiDAR' technology in the mode of Terrestrial Laser Scanning (TLS) and Airborne Laser Scanning (ALS) find rapidly growing interest in remote sensing and photogrammetry field as efficient tools for fast and reliable three-dimensional (3D) point cloud data acquisition. These laser techniques obtains the 3D reconstruction of objects; the measure of the distance from the platform (eg. ground-based for TLS, airplane or helicopter for ALS) derives generally from the time employed by the laser beam to go and to come back (time-of-flight principle). This paper describes the capabilities of TLS and ALS in slope mapping studies. The study has been conducted at two test sites, namely Tanah Rata and Habu, Cameron Highland, Malaysia. Several data acquisitions on selected cut slopes were performed using the TLS instrument: Topcon GLS1500. Ground control points were established using Real Time Kinematic GPS to provide a local coordinate system on laser scanning data. The ALS raw data was provided by a private mapping company. This study shows the ability of TLS and ALS to obtain reliable 3-D slope information over unstable area.