A Bird Calibration Device of Helicopter‐Borne TEM with a Concentric Bucking Loop

Abstract

AbstractThe multiple instrument calibrations of flying helicopter‐borne time‐domain electromagnetic method (HTEM) can eliminate the environmental time‐varying effect on the system during flight. Using the bird calibration device to solve the problem that the wire‐loop method can't achieve, this paper considers the bird model of HTEM with the concentric bucking loop, bringing forward the bird device space models and the coil circuit models, and analyzing the transmitter magnetic field distribution, the bucking loop's effect and the relationship between it and the receiving coil, the space information of the calibration device and its signal detected method. Conclusions are as follows: (1) The bucking loop that loses 0.89% of the transmitting area can increase 44.5 dB of the signal dynamic range. (2) The calibration device is horizontally placed between the bucking loop and the transmitting coils. If it has more turns and greater radius and is closer to the bucking loop, its signal response becomes stronger. (3) When the inductance of calibration coil, with less resistance, becomes greater, its exponential decays more slowly. The signal detection time point is directly decided by damping character of receiver coil which had matching resistance. We did experiments about the calibration curve characters and the device coil displacement. The relative error about the time constant of the device characteristics is less than 1.3%, which proves the validity of the coil circuit models and device space models. The proposed models and approaches are also the same with the bird calibration device research about HTEM with the eccentric bucking loop and the known wire‐loop static tests on the high‐resistance formation.