DC, EM & NMR technologies

[DE-01] Drone Electromagnetic Survey for Slope Subsurface Structure Investigation –Flight along Steep Slope

*Yohei Morifuji¹, Kenji Kubota¹, Shiro Tanaka¹, Hiroshi Suenaga¹, Akira Jomori², Atsuyoshi Jomori², Tetsuya Toyama² (1. Central Research Institute of Electric Power Industry (CRIEPI) (Japan), 2. Neo Science Co., Ltd. (Japan))

A drone electromagnetic survey (D–GREATEM: drone–grounded electrical source airborne transient electromagnetic system) was conducted on a steep slope to identify the resistivity structure. Originally, a drone electromagnetic survey could only fly at a constant flight elevation. However, technological advances have enabled drones to fly along slopes. We show the results for two flight patterns and confirm the improvement. In the first flight pattern, the survey line was divided into two sections. The drone was operated at two flight elevations (EL.); section 1 was EL. 360 m and section 2 was 285 m. The second pattern involved a flight along the slope to keep the distance from the surface constant. In the first pattern, the resistivity values at the same receiver point were different owing to different flight altitudes. In the second pattern, no gap was observed in the resistivity structure. The results showed three layers of resistivity, i.e., a higher resistivity zone at depths shallower than 30 m (more than 2500 Ωm), a lower resistivity zone from 50–120 m (200–600 Ωm), and a higher resistivity zone at greater depths (more than 600 Ωm). The shallowest higher resistivity zone indicates detritus and talus deposits distributed near the surface, which is consistent with the borehole data. The ground electrical resistivity survey also indicated a higher resistivity zone in the area. Thus, drone electromagnetic surveys can be used to easily obtain the resistivity structure of slopes.