Three-dimensional modeling of semi-airborne transient electromagnetic with loop source

The semi-aeronautical transient electromagnetic detection can be realized by laying a loop on the ground to excite the transient electromagnetic signal and by using the UAV receiving coin in the air to obtain the transient electromagnetic attenuation signal. However, compared with the traditional ground-based transient electromagnetic, there are many factors affecting the semi-airborne transient electromagnetic detection, such as flight altitude, receiving offset and so on. Based on the grid meshing in three-dimensional transient electromagnetic using finite difference time-domain (FDTD), the three-dimensional forward response law of semi-airborne transient electromagnetic with loop-source on the ground launching and UAV receiving in the air is studied in this paper. Firstly, the uniform half-space model and layered model are used to study the morphological characteristics of the semi-aeronautical transient electromagnetic field curve. By studying the curve at different receiving heights, it can be found that the influence of receiving height is mainly concentrated in the early stage and tends to coincide in the late stage, and that as the resistivity value increases, the amplitude of the voltage curve decreases. By studying the curve at different offsets, it can be found that as the offset increases, the amplitude of the decaying voltage curve gradually decreases and that the response is mainly concentrated in the early time. For the layered model, the semi-aviation transient electromagnetic can effectively identify the formation resistivity changes. Finally, by studying the semi-aeronautical transient electromagnetic response of the 3D geo-electric model, four geological models including low resistance anomaly A model, low resistance anomaly B model, mixed low resistance anomaly model, and high resistance and low resistance anomaly model are designed. By changing the acceptance height, size and depth of the abnormal body, and the offset of semi-aeronautical transient electromagnetic, it is found that the semi-aeronautical transient electromagnetic voltage response curve is mainly affected by the receiving height, and the decay voltage curves tend to coincide in the late stage. However, when the abnormal body is relatively shallow buried, the response to the buried depth of the anomalous body is less obvious. The response to the offset is similar to the effect of the receiving height, both concentrated in the early stage of the decay voltage curve. © 2019, Editorial Office of Journal of China Coal Society. All right reserved.