2021 Volume 74 Pages 115-122
The use of unmanned autonomous vehicles (UAVs) for volcanic observations has received attention since the beginning of this century, as they enable various kinds of measurements to be carried out without a risk of human casualties. The UAVs can fly along pre-programmed routes with high positional accuracy as much as tens cm, and thus a setup of ideal measurement lines can be realized, for example, to keep constant altitudes above ground and spatial intervals of measurements, and to make repeated observations along the same measurement lines at certain time intervals to detect the temporal change of the observables. In this study, an autonomous driven unmanned helicopter was used to conduct aeromagnetic surveys in volcanoes to keep a constant spatial resolution of geomagnetic field measurements over a complex terrain, and to detect changes in the geomagnetic field caused by volcanic activities. At Mt. Mihara, Izu-Oshima island, high magnetization zones were identified around the central cone, which is considered to have been solidified underground and not erupted in the past. At Mt. Shinmoe-dake, Kirishima, we could clearly detect the magnetization of the lava in the crater over time due to cooling through repeated aeromagnetic surveys since the 2011 eruption. The development and use of drones have been remarkable in the last few years, and volcanic observations by UAVs are expected to mature in the future.
