Abstract
The transient electromagnetic (TEM) method is widely used in shallow surface engineering geological surveys due to its advantages such as light weight, high efficiency, and strong resolution. However, interpretation and inversion of TEM data is a complicated process. The traditional algorithm of TEM inversion employs the “smoke ring” fast imaging method, which can only reflect the approximate morphology of the stratigraphic model, and the inversion accuracy is low. Therefore, this method cannot meet the requirements of high-precision inversion. In this article, we present the particle swarm optimization (PSO) algorithm for TEM inversion. First of all, the response of the rectangular loop source TEM based on electric dipole integration was calculated and compared with the analytical solution results of the rectangular loop source and the accuracy of the algorithm was verified. Then, we introduced the solution process of the particle swarm optimization algorithm and analyzed the influence of particle swarm optimization algorithm parameter selection on the accuracy of the inversion result and the convergence speed. Next, a layered medium model was established. The particle swarm optimization algorithm and “smoke ring” fast imaging method were used to perform inversion calculation. The results show that the PSO algorithm has the advantages of high efficiency and accuracy. Finally, we examined the effectiveness of the particle swarm optimization algorithm for TEM data processing by inverting survey data from an Air-raid shelter on the campus of Chongqing University in China and comparing the results with those from the “smoke ring” fast imaging. The research works in this article provide new methods and techniques for TEM data processing.
Highlights
The transient electromagnetic (TEM) method is a time-domain electromagnetic method based on the difference of conductivity and magnetic conductivity of subsurface media
The transient electromagnetic method is widely used in deep resource exploration as a non-invasive geophysical method with the advantages of light weight, high efficiency, and strong resolution [3]-[4], Urban Engineering Geological Survey [5]-[6], Coal Mine Water Inrush Survey [7], Tunnel Geology Advance forecasts [8] and underground metal objects Survey [9]
The traditional algorithm for transient electromagnetic method inversion employs "smoke ring" fast imaging, which only reflects the approximate morphology of the stratigraphic model and accuracy is low
Summary
The transient electromagnetic (TEM) method is a time-domain electromagnetic method based on the difference of conductivity and magnetic conductivity of subsurface media. The PSO method encounter a premature convergence when solving a complex optimization problem, this is due to the improper balance between the local and global searches. To solve such difficulties the quantum version of particle swarm optimization (QPSO) and multi-objective version of particle swarm optimization was proposed [32]-[33]. Its first application of particle swarm optimization algorithm in geophysical method stems from its successful application in the solution and appraisal of the vertical electrical sounding inverse problem by Fernández-Á et al [34]. We demonstrated the effectiveness and accuracy of the PSO method for TEM inversion by both synthetic data and survey data and by comparing the results with those from the "smoke ring" fast imaging
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