Research on three-component response of ground-airborne TEM considering emission current waveform

The ground-airborne TEM has received more and more attention in coal goaf exploration and other fields. In order to provide a theoretical basis for the processing and interpretation of ground-airborne transient electromagnetic data, it is necessary to study the influence of the transmitted current waveform parameter on the three-component response characteristics of ground-airborne TEM. Taking trapezoidal waves as an example, this article firstly studies the frequency distribution of different emission current waveform, and then investigates the effects of the rising edge time, pulse width and turn-off time of the transmitted waveform on the three-component magnetic field response of ground-air transient electromagnetic based on the three-dimensional finite difference time domain method(3D-FDTD). The results show that the rising edge time basically has no effect on the three-component secondary field response; the turn off time effect on the three-component secondary field response is mainly concentrated before 0.2 ms, and the longer the turn off time, the greater the impact on the pure abnormal response; the pulse width has the main effect on the three-component secondary field response after 0.1 ms, and the shorter the pulse width, the greater the impact on the pure abnormal response. The results of the three-dimensional goaf model show that the characteristics of the off-time and pulse width on the response of the three-component abnormal field and background field are basically the same; the distribution range and depth of anomalous objects can be judged by the three-component pure anomaly field response multi-track map and time track map. The research results will provide some valuable theoretical references for the selection of the parameters of the ground-airborne TEM excitation source waveform.