2019 Volume 30 Issue 3 Pages 101-109
In recent years, due to climate change, heavy rainfall has occurred frequently, and the damage caused by inundation has increased. However, the soundness of the levee is done by the visual inspection while experts walk. Therefore, it is evaluated depending on the skills and experience of the experts. There has been a need for a method that can monitor the outer shape of the levee in detail in normal times and after flooding, and to conduct quantitative evaluation for taking measures immediately if abnormalities such as deformation are found. Mobile Mapping System (MMS), which is equipped with a laser scanner on a vehicle, has attracted attention as a method that can quickly carry out high-precision surveying. When the survey is conducted by using MMS that travels on the levee crown, a dead angle of laser irradiation occurs. It is possible to detect the subsidence of the levee crown with high accuracy, but it is not possible to detect where it is necessary to take measures in the whole levee including the slope surface by using MMS survey. In this paper, we clarified what kind of problem the dead angle of the laser light leads to, and discussed the advantages of acquiring 3D data for grasping the topography of the levee by irradiating the laser from a high position. We showed the relation between the laser irradiation angle and the traveling speed of the vehicle and the surveying accuracy, and considered the position to install the laser scanner device to acquire the 3D data up to the slope toe area. We also verified the effectiveness of the laser surveying which irradiates from the 5.5m height. In comparison with the conventional laser surveying by vehicle travel, it was demonstrated that the method we considered was efficient as a surveying work and detected a detailed deformation on the slope surface because it provided high density laser point clouds. Since the heavy rainfall of short duration will increase in the future, it is expected that the results of this study are considered to be useful as a method for efficiently grasping the topographical features of the levee.
