SOURCE EXTRACTION OF ROCKFALL BY MICROTOPOGRAPHY HIGHLIGHT MAP VIA HIGH-DENSITY AERIAL LASER SURVEY

Investigations using maps that reflect slope conditions have been conducted for slope inspection. However, oversight at the time of inspection has become a problem owing to unsatisfactory map performance. This paper presents a microtopography highlight map created using a high-density aerial laser survey as a new inspection tool and evaluates the influence of survey conditions on a desk study of rockfall sources using the map to develop an efficient slope inspection method. The microtomography highlight map is created by the combination of a slope map, which displays the slope angles, and a wavelet analysis map, which displays the unevenness of the slope. The slope and wavelet analysis maps are created via terrain analysis based on the digital elevation model, which is created using aerial laser survey results. In this study, we demonstrated slope inspection using a map of grid size 50 cm on two slopes where there was a risk of falling rocks. A comparison of the desk study and field research showed that using the map was effective in extracting the source of the rockfall (>2 m height). In addition, the verification results showed that the measurement conditions affect the representation of the map, and that the measurement should be conducted in winter to produce a more detailed map, which leads to effective inspection.