Journal of the Korean Society of Mineral and Energy Resources Engineers ISSN:2288-0291(Print) 2288-2790(Online) 한국자원공학회지

The quasi-linear series is based on the assumption that the anomalous field is linearly related to the background field in the inhomogeneous medium through an electrical reflectivity tensor. The reflectivity tensor, slowly varying functions of position and frequency, are determined numerically by a simple least-squares method. Also, quasi-linear series converges always for any lossy background medium since it uses a linear integral operator with the norm less than 1 as like as a modified Born series. In this study, the results of 3-D EM modeling based on the extended Born, the modified Born series and the quasi-linear series are compared with that of full integral equation method. The results of all the methods give an accurate estimate of the 3-D EM response for a strong contrast up to 100 times and for a wide range of frequencies. It has also been shown that these methods are much faster and demand less memory than the full integral equation method. Among the three approximation methods, the extended Born approximation is fastest and the quasi-linear series shows the most accurate result. The modified Born series requires less time than the quasi-linear series of the same orders. However, to reach the same accuracy, the modified Born series of higher orders should be calculated than in the case of the quasi-linear series. Therefore, the quasi-linear series and the extended Born approximation are very effective approximation tools for 3-D EM modeling and inversion.