Design of an airborne concentric frequency-domain electromagnetic induction system for shallow subsurface geophysical exploration

For the exploration of shallow and small subsurface targets, rigid-beam helicopter-borne electromagnetic systems are often inconvenient or costly, whereas man-portable or ground-based systems are difficult to operate in complex terrain. An airborne concentric frequency-domain electromagnetic system with an unmanned rotorcraft as a flying platform is proposed to avoid the problems of low security in conventional helicopter-borne electromagnetic method and low efficiency in ground-based electromagnetic method for the exploration of shallow subsurface targets. Compared with the series mode of man-portable system, the currents of transmitting and bucking coils are assumed to be separately and continuously adjustable, which can reduce sensitivity of the small errors of the system. In this paper, the principle of canceling the primary magnetic field is analyzed. The design index of the physical parameters of the sensor is determined. The simulation experiment of layered earth model is carried out to verify the feasibility of the proposed system.