Rockfall inventory map for efficient slope inspection via aerial laser survey and signal processing techniques

Investigations using maps that reflect slope conditions have been conducted as measures against falling rocks. However, owing to the limitations of map performance, oversights during the inspection have become a major cause of concern. To overcome this, and implement high-quality inspections, it is important to use clearer maps. Herein, aerial laser surveying and geomorphological analysis have been conducted to achieve this objective. Aerial laser surveying is implemented for measuring a wide area from the sky using an aircraft equipped with sensors. Recorded measurement data is three-dimensional and is represented by a collection of points with three-dimensional coordinates. Moreover, geomorphological analysis is used for extracting the terrain from the data (such as the unevenness of the terrain), and the map is created by expressing the analysis results in two-dimensional space. To establish an efficient inspection method, a map was created using two-dimensional wavelet transform in signal processing technology as a geomorphological analysis method and aerial laser surveying. For verification, we focused on understanding the usefulness of the as-obtained map and determine the relationship between measurement conditions and conditions during mapping. The results show that 1) the created map can extract the rockfall source from the target slope comprehensively, 2) even if the ground data point density is low, if the inflection point of the targets can be confirmed, it can be expressed on the map depending on the analysis conditions, and 3) the rockfall source expressed on the map changes with the relative height due to changes in measurement conditions and parameters.