A Helicopter Inboard Magnetic System - A World First

This paper describes an aeromagnetic survey system installed in a Squirrel helicopter. To date, magnetic surveying done with helicopters has involved magnetometers carried in towed birds or more recently, a pair of magnetometers suspended in a vertical gradiometer array. The configuration described here consists of a magnetometer mounted at the end of a forward-facing boom mounted between the helicopter skids. This "inboard" system, as opposed to current towed systems, is the first of its kind. Compared to a fixed wing aircraft, a helicopter is a very concentrated collection of magnetic material and the magnetometer had to work in proximity to disturbing magnetic fields that were much stronger than normally encountered in fixed wing installations. Considerable effort was expended to reduce stationary magnetic interf7rence and to eliminate completely non-stationary fields. Finally, the key to reducing the high levels of residual magnetism was a comprehensive compensation system. Improvements in signal to noise between uncompensated and compensated total field signal were by a factor that exceeded 100. The work described in this paper resulted in a fully operational magnetic survey system that has proven its usefulness in a year of successful low-altitude survey projects that have been characterized by a high degree of client satisfaction.