Study On Reverse-time Migration Imaging Of Transient Electromagnetic Method

Transient electromagnetic method(TEM),or time domain electromagnetic method,is a very important electromagnetic exploration method.Compared with other electromagnetic exploration methods,this method has the advantage that TEM is sensitive to the exploration of low-resistivity bodies,and is not affected by the terrain when working,and has a higher signal-to-noise ratio.However,the disadvantage is that it is difficult to carry out data processing and inversion,so it needs further research and development in this aspect.At present,the inversion technology of TEM is developing rapidly in China,but the inversion method and imaging technology are still the focus of research.Some scholars have proposed a quasi wave equation migration imaging method suitable for transient electromagnetic field,but its theory and process are complicated.In the introduction part of this paper,the research status of forward modeling and inversion of TEM at home and abroad and the research status of migration imaging technology of TEM are introduced.And then introduce the basic principle of transient electromagnetic method to detect and working principle,starting from the Maxwell's equations,deduced the wave equation,introduced the finite element method,and explained the working principle of transient electromagnetic method.Several working devices such as central loop device,overlapping loop device,excitation waveform parameters and observation are also introduced.In the forward research,introduced the three dimensional numerical simulation software CST,powerful processing function of the software are introduced,boundary conditions,tetrahedral grid section technique,the adaptive grid subdivision technology,the advantages of the solver and varied,and introduced the use of this software to simulate the operation process.And three dimensional numerical simulation was performed several times,thus the central loop transient electromagnetic 3D geological body theory response results were obtained.In the aspect of inversion,the conventional TEM reverse-time migration method is introduced firstly,and the advantages and disadvantages of Stratton-Chu integral migration method and Kirchhoff integral migration method are listed.Then,on the basis of the electromagnetic wave propagation in the earth is much lower than the speed of propagation speed in a vacuum of the properties,the reference earthquake reverse-time migration technology,put forward a superposition of wave field imaging based on ray theory,new ideas,and in view of the central loop transient electromagnetic method,observation way,the corresponding algorithm is designed,using C# language to write code that implements the algorithm.Finally,the forward simulation response results are used to verify the results.Results show that the proposed reverse-time migration imaging algorithm is a relatively effective data processing method,this method is simple,fast,and don't need a lot of calculation.However,the verification effect in this paper is not good,so we need to further optimize and improve in the future.Finally,the shortcomings of the paper and the future research direction are described.