Understanding Topography and Geological Structure Based on Drone Photogrammetry and Verifying Its Usefulness: A Case Study of the Median Tectonic Line on the East Bank of Lake Miwa, Ina City, Nagano Prefecture, Central Japan

Drone photogrammetry is carried out with an SfM-MVS analysis to obtain detailed topographic data and to make digital elevation models (DEMs) on a peninsula on the eastern shore of Lake Miwa, Ina City, Nagano Prefecture, where the topographic features and geological boundaries of the Median Tectonic Line are well observed. In the area covering the entire peninsula with several hundred-meter scales, the resolution of the DEMs produced by drone photogrammetry in this study is higher than that of 5-10 m mesh DEMs available free of charge. At the Mizoguchi outcrop on the southern edge of the peninsula, which is exposed on a several tens of meters scale with the clear lithological boundaries of the Median Tectonic Line, DEMs obtained by drone photogrammetry show a higher resolution than a 0.5 m mesh DEM constructed from airborne laser scanning. These results demonstrate the high utility of drone photogrammetry for a topographic analysis of an area within a few hundred meters of scale. In addition, the orientation of the lithological boundary at the Mizoguchi outcrop, estimated based on DEM images, agrees with that measured at the outcrop using a hand-held clinometer. This indicates that an analysis of geological structure using drone photogrammetry is practically feasible. Considering the advantages of cost and portability, it is suggested that drone photogrammetry may be a suitable approach for structural analyses in geological field surveys that require investigations in harsh environments such as steep mountain areas.