Multi-line Source Multi-component Response Characteristics Of Ground-space Transient Electromagnetic Method

The specific device mode and detection method of ground-to-air electromagnetic method combine the respective advantages of ground-to-air electromagnetic method and aviation electromagnetic method,It has high field construction efficiency and detection accuracy,and can quickly,large-scale and high-precision exploration of goaf in complex terrain areas that are difficult for workers to enter,which can realize high-efficiency,high-altitude and high-depth exploration,especially in some mountainous areas with rugged terrain and difficult detection.At present,although the ground-air transient electromagnetic method has developed rapidly,its application in practical engineering is still less.Most of the existing detection methods use single excitation line source,which can only be coupled with geological body from one side in practical work,and it is difficult to obtain holographic images of geological body.However,using multiple excitation line sources can effectively solve this problem.In order to study the response characteristics of multi-excitation line sources in ground-air transient electromagnetic method to the detection of mined-out abnormal areas under different geological bodies,To improve the detection accuracy and enrich the ground-air electromagnetic detection technology system,this paper uses theoretical analysis and numerical simulation methods to simulate the ground-air transient electromagnetic response under multiple excitation line sources of mined-out area anomalies under different geological bodies.Firstly,the forward simulation calculation theory and method of electromagnetic detection in ground-air time domain are studied,Based on the unstructured mesh finite vector element method,Using COMSOL simulation software,the simulation geoelectric model of three-dimensional ground-to-air electromagnetic method is established,By comparing with the analytical solution of uniform half space,The correctness of the modeling and solving method in this paper is verified,Based on the forward simulation,this paper analyzes the effects of single excitation line source and different multi-excitation line sources on the number and setting mode of excitation sources,The response characteristics and influencing factors of magnetic field components in X,Y and Z directions generated by mined-out abnormal bodies in the air under different surrounding rock resistivity,different offset,flying height and different overburden layers are simulated and analyzed.The advantages of multi-excitation line source over single excitation line source and the influence of different factors on the detection response of ground-air transient electromagnetic method are obtained.The results show that: 1)STAM can not only enhance the signal of induced magnetic field,but also obtain more comprehensive information of geological body from different angles,and identify the range and boundary of abnormal body more accurately;Among them,the detection effect of double cross line source and rectangular line source is obviously better than other double emission sources.When the emission line source passes through the space directly above the abnormal body,the recognition effect of the abnormal body is better;2)Both Z and X component data can be used to identify the location and range of low resistivity anomaly effectively.Directly above the anomaly,Z component shows high electromagnetic response anomaly,and X component shows polarity reversal above the center of the anomaly and the response intensity is the lowest.Ground-to-air transient electromagnetic method has no obvious detection effect on underground high resistance abnormal body;3)The change of flight height in a certain range has little influence on the response results;4)The change of resistivity of overburden and surrounding rock has influence on the detection results;5)Under different line sources with the same total length,multi-excitation line sources have better detection ability for abnormal bodies;6)Excessive offset is not conducive to data acquisition and signal processing interpretation,and the near-field area close to the line source has certain interference effect on detection.It is suggested that in practical work,the offset of the working area should be controlled within 2-4 times of the side length of the emission source layout area.Compared with single excitation line source,this paper verifies the advantages of multi-line source in signal quality,detection efficiency and target recognition.It not only lays a foundation for high-efficiency,high-quality and high-precision ground-to-air electromagnetic detection methods,but also provides theoretical guidance for multi-source field implementation and deployment.