2021 Volume 74 Pages 142-150
Airborne electromagnetic (AEM) survey methods can be divided into two types: 1) AEM survey methods, in which a transmitter is installed on the ground and measurements are made in the air, and 2) methods in which electromagnetic waves are transmitted from the air and received in the air. The drone exploration method has been developed and put into practical use. Ground-source type airborne electromagnetic survey method (D-GREATEM) installs a transmitter on the ground during the exploration. D-TEM is also in practical use, and has both transmitter and receiver in air and measures by flying two drones simultaneously. One drone towing transmitter and other a receiver. D-GREATEM and D-TEM were conducted to understand the geological structure and hydraulic properties in the Seino area of the Nobi Plain in order to develop a groundwater utilization system for use during the event of major earthquake or other disaster.
D-GREATEM survey was carried out in two flight lines continuous from the mountainous area to the alluvial fan and D-TEM survey on one flight line in the alluvial area during the high and the low rainfall seasons. The same positions of flight lines were reproduced by using programmed flight. The geological structure, faults, and groundwater were estimated by calculating the difference in rate of change from the results of the two surveys and comparing them with previous data. Although each survey method has its own challenges and limitations, it was confirmed that the geological model, faults and groundwater level changes can be understood from the exploration results.
The drone AEM method has a larger amount of data than other survey methods that can easily obtain detailed three-dimensional information of the subsurface. Since the same measurement conditions can be reproduced by the automatic flight of the drone, four-dimensional exploration with time variation is possible. It is expected that the drone airborne electromagnetic survey technology will contribute to geological surveys in various fields in the future.
