Many Anomalies Response Characteristics Of The Underground TEM Of Three-dimensional FDTD

In recent years the study of whole-space transient electromagnetic method(TEM) has developed rapidly,which is used to predict water inrush structures nearby the roof, bottom and driving face in roadway.The applied effect, economic performance and social benefits have been acknowledged,which it has much room for development and application research value.In basic theory and data interpretation,the 3D forward of ground TEM has made good results,which can provide guidance for the whole space.There have mang scholars are studying the 3D forward of mine TEM.But the goal of their research forward is a single body in the country rock,what are difficult to reflect the true geological which the response of two or more bodies in the country rock,it difficult to obtain the true subsurface situation.These theoretical problems,transient response for the typical geologic geophysical model in whole-space are studied,forward simulation is studied in full spatial response when have many bodies of low resistance or low-resistivity layer in the country rock in this paper.The 3D whole-space response characteristic of the sheet conductive body located in uniform medium has been imitated with a magnetic dipole,and adopting the 3D time domain finite-difference formula to calculate.Two anomalies when they are existing simultaneously,the 3D whole-space response characteristic under the influence of laneway have been imitated.Analysis propagation regular patten that the transient electromagnetic field located in uniform and layered medium.First of all,models are created in the unform medium,two abnormal bodies are juxtaposed and superimposed in the surrounding rock.When two anomalies exist side by side,there is no mutual interference between the two.What can be identified two abnormal bodies early,and contours of the electric filed are squeezed strong by two resistance.When a low-resistivity body is covered with other low-resistivity body, only can distinguish anomaly body which closer to roadway at an early stage.When the time is late stage,the other low resistivity body can be distinguished vaguely.With a single low-resistivity comparative,the results show that,TEM energy is absorbed by the low-resistivity body larger when through the body,the energy becomes weak when it penetrate past.Then,models are created in the layered medium.A geological layer of high-or low-resistivity is inserted in rock,make the dielectric layer lying between roadway and abnormal body.When the high-resistivity layer lying between roadway and abnormal body,no matter how anomalies are placed in the rock,the results obtained is the same with that there have no high-resistivity layer in the rock.But,when the low-resistivity layer lying between roadway and abnormal body,influence is very great for low-resistivity bodies.In the early stage the impact of low-resistivity layer is serious to identify anomalies,even in the interim stage,the impact still exist,the field of TEM attenuations slowly in strong electrically conductive medium,resulting time stay too long in the low-resistivity layer.When low resistivity bodies are superimposed in the rock,low resistivity body is not can be distinguished when it farther away from the roadway.