Development and Application of the Frequency-domain Airborne Electromagnetic Method in China
Zhou Fengtong, Liu Weiguo, Man Yanlong, 1989. "Development and Application of the Frequency-domain Airborne Electromagnetic Method in China", An Overview of Exploration Geophysics in China — 1988, Zhao Jingxiang, Wang Yanjun, Fu Xuexin, Stanley H. Ward
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The current development and direction of the airborne electromagnetic (AEM) method in China are briefly reviewed. Experience in developing the frequency-domain airborne electromagnetic systems (FAEM) is introduced. Technical problems encountered in developing FAEM systems, such as the interference from the receiving system, the secondary fields due to the body of aircraft, and the noise due to wing flexure, are described along with the measures used for solving the problems. The mounting for a receiving coil and the coils damping device must be designed with the inherent vibration frequencies differing from those of the FAEM system. By shielding the ignition system and high voltage cables, interference due to the electric equipment of an aircraft can be reduced 15 to 20 percent. To suppress interference due to the metal parts of an aircraft, coils should be placed as far from the wing tips as possible to ensure that resistance of the electrical joints and the associated contact resistance are less than 100μΩ. For FAEM systems of wing-tip type, a formula for mounting transmitting and receiving coils on the tips of aircraft wings to suppress as much as possible noise due to wing flexure is given for an optimum altitude. A set of thermal sensors was mounted in the Y-11 DFAEM system to monitor temperatures, based on our finding that the long-term drift is related not only to the environmental temperature but also to the process of reaching thermal equilibrium.
Using the Y-11 system, a fresh-water region over the subsurface reservoir at the Nangong area of Hebei was mapped, and about 300 fracture zones were outlined in the Zhaoyuan area of Shandong Province, a well-known gold prospect. Some newly discovered gold areas are controlled by the interpreted fracture zones.
A suggestion that long-term drift may be suppressed by setting a surface base station or base net is discussed.