HR: 0800h
AN: NS31A-0151    [Abstracts]
TI: Aeromagnetic survey by a model helicopter at the ruin of ironwork refinement
AU: * Funaki, M
EM: funaki@nipr.ac.jp
AF: National Institute of Polar Research, 9-10 Kaga 1 Itabashi, Tokyo, 173-8515, Japan
AU: Nishioka, T
EM: nishioka_t@hirobo.co.jp
AF: Hirobo Co., 3-3-1 Sakuragaoka Fuchu Hiroshima, Fuchu, 726-0006, Japan
AB:  It is difficult to detect the magnetic anomaly resulting from the small scale of magnetic sources as archeological or historical ruins by a helicopter due to the restraint of the low altitude flights in the narrow area. Although a relatively small unmanned helicopters has been commercialized for agriculture use etc., it is too expensive for aeromagnetic surveys. We have developed a small autonomous unmanned helicopter which modified a model helicopter for aeromagnetic survey. A model helicopter (Hirobo Co.; SF40) with a 40cc gasoline engine, length of 143cm from the nose to the tail and dry weight of 15 kg is selected in this study. The irradiated magnetic field from the bottom-center of skid of SF40 was the total magnetic field (R)=3511 nT, inclination (I)=12 degrees and declination (D)=138 degrees. It was reduced to about 1 nT at 3 m downward from the skid during the hovering. When SF40 was covered with a magnetic shield film (Amolic sheet), the distance to measure 1nT diminished to 2 m. As shielding whole body with the film is not effective for reliable and safety flights, the only servomotors having the strong magnetization were shielded by the film. The autonomous flights based on GPS data succeeded. As the control system was too large and heavy for SF40, we are developing more simple and small navigation system for this project. Magnetometer system consists of a 3-axis fluxgate magnetometer, data logger, GPS and battery, recording every second of x, y and z magnetic fields, latitude, longitude, altitude and satellite number during 3 hours. The total weight of the system is 400g. The system was hanged to 2m lower from the skid by a rope (Bird magnetometer) or 2m front form the nose by a carbon fiber pipe (Stinger magnetometer) in order to avoid the magnetic field of SF40. However, the bird magnetometer was not suitable due to the strong noise resulting from the swing of the sensor. An archeological ruin of the ironwork refinement aged 15th century in western Japan was measured by the stinger magnetometer. The survey area was 70x20m with a gentle slop. The helicopter was controlled by the manual keeping up the roughly same altitude (the 4-8m height from the surface) and speed (1m/s). The result showed the strong anomalies of 500 nT at the NW corner of the area where consists with the refinement. From these viewpoints the model helicopter is useful to find the ironwork refinements instead of the identification based on the feeling and the experience of archeologists.
DE: 1503 Archeomagnetism
DE: 1517 Magnetic anomalies: modeling and interpretation
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting