For the development of an airborne electromagnetic prospecting method capable of deeper exploration, a basic study was made about a system wherein a transmitter (source) is positioned on the ground and the receiving is done in the sky. Even in case of this airborne electromagnetic method, the TDEM method is supposedly advantageous over others as in case of groundborne exploration. In the study, the transient response of an airborne vertical magnetic field to a horizontal layered structure was calculated. The current source was 2000m long with a capacity of 30A. The one-layer structure was a 10 Ohm m semi-infinite ground, and the two-layer structure had a 100 Ohm m structure just under the one-layer structure. The result of the calculation suggests that, in the absence of a layer of extremely low resistivity, observation of an approximately 1 second long transient response aboard a helicopter flying at approximately 50km/h will enable an approximately 1000m deep exploration. Problems to affect airborne observation, such as swinging, natural magnetic field fluctuation, and artificially produced noises were investigated by use of a magnetometer suspended from a helicopter in flight. 2 refs., 6 figs.
Mogi, T;  Shimoizumi, M;  Kusunoki, K;  Morikawa, T;  Jomori, N 
- Kyushu University, Fukuoka (Japan). Faculty of Engineering
- Kitakyushu Polytechnic College, Kitakyushu (Japan)
- Central Research Institute of Electric Power Industry, Tokyo (Japan)
- Dowa Engineering Co. Ltd., Okayama (Japan)
- Chiba Electronics Research Institute, Chiba (Japan)