Transient Electromagnetic Method Based Location Of A Penetrator Along Soil Medium

Earth penetrator is a kind of guided weapon to attack the command center or fighting bastion precisely on the ground or underground. The sturdiness and underground of important military targets, greatly promote the research and development of penetration technology and earth-penetrating weapons. In the testing research of the penetrator in the rang experiments, the detection, location, digging and recycling of warheads in the soil is the basis of studying the shape design, penetration index and motion performance of earth penetrators. However, the inhomogeneity and invisibility of underground medium, the uncertainty of temperature and humidity, the difference of each point permeability and the changing of underground medium in the process of penetration, seriously affected the positioning precision and efficiency of general positioning methods such as infrared ray,seismic waves, ground penetrating radar for underground in the detection of earth penetrators.Transient electromagnetic method is a kind of time domain electromagnetic prospecting method, it detects abnormal targets different from the background or environment on the basis of that different media have different secondary magnetic field attenuation characteristics.Compared with general detection methods, transient electromagnetic method is convenient and repeatable to operate, has sensitive response to good conductor,strong penetrability to the soil layer and aquifer, the signal is simple to analyze, and it has already applied to a lot of geological prospecting fields, such as metallic mineral exploration, underground mined-out areas exploration, oil and coal mine and other non-metallic mineral survey, archaeology. This paper carries out the feasibility studies of detecting the location of earth penetrators in the soil medium using transient electromagnetic method.According to the detection principle of transient electromagnetic method, the paper studied the response signal during the process of transient electromagnetic from the angle of the circuit in the first place, divides the received induction electromotive force into induction section and attenuation section which is divided into decay early and late, analyzes the characteristics and significance of the response signal each phases, discusses the minimum and maximum detecting depth of the transient electromagnetic method and its influencing factors, and analyzes the conditions of the transient electromagnetic method to detect earth penetrators in the soil. Then, a three-dimensional numerical analysis model of transient electromagnetic method detecting earth penetrators is created through the finite element simulation software COMSOL, and the influence of the observation time, the cut-off time of the excitation current source, the size and depth of the earth penetrator to the transient electromotive force from the receiving coil is studied in the article. Finally, this paper does the multi channel sampling to the late attenuation induced electromotive force in the horizontal plane, confirmes the projection position(x, y) of earth penetrators on the horizontal ground due to the sample curve and surface figure, fits out the experience formula of the depth and size of the earth penetrator through the inversion; and get the projection range and the depth information of the earth penetrator on the vertical profile and analyzes the angle of the earth penetrator in the soil layer through the late transient electromagnetic apparent resistivity section map; then obtaines the quantitative relationship between the main parameters such as buried depth, radius, decay time of the earth penetrator and the late induction electromotive force.