Numerical analysis of multi-source and multi-component response characteristics in the semi-airborne transient electromagnetic method

The semi-airborne transient electromagnetic method (TEM) detects geological structures with a single transmitter field source, which receives only the vertical component of the magnetic field and is unsuitable for detecting complex geological structures. This study proposes a three-dimensional vector finite element method in the time domain for analyzing and comparing the three-component response characteristics of multi-transmitter-source TEMs with different types, quantities, setting methods, surrounding rock resistivity conditions, and receiving offsets. Four major findings emerged from the study. First, the semi-airborne TEM detected underground low-resistivity anomalous bodies much more effectively than high-resistivity anomalous bodies. Second, after deploying multiple transmitter sources in the semi-airborne TEM, the intensity of the induced magnetic field increased and the distribution law of the secondary field electromagnetic response of an abnormal body better matched that of the original model. Third, the range of low-resistivity anomalous bodies can be effectively identified from the z and x components of the electromagnetic response. Directly above the anomaly, the z component shows a high electromagnetic response while the x component shows polarity reversal and a minimal response. Fourth, excessively large offset values deteriorate the data acquisition and signal processing interpretation. Controlling the offset of the working area to within 2–4 times the side length of the transmitting-source layout area is recommended in practical applications.