Browse > Article
http://dx.doi.org/10.7582/GGE.2014.17.3.129

Frequency-to-time Transformation by a Diffusion Expansion Method  

Cho, In-Ky (Department of Geophysics, Kangwon National University)
Kim, Rae-Yeong (Department of Geophysics, Kangwon National University)
Ko, Kwang-Beom (Korea Resources Corporation)
You, Young-June (Korea Resources Corporation)
Publication Information
Geophysics and Geophysical Exploration / v.17, no.3, 2014 , pp. 129-136 More about this Journal
Abstract
Electromagnetic (EM) methods are generally divided into frequency-domain EM (FDEM) and time-domain EM (TDEM) methods, depending on the source waveform. The FDEM and TDEM fields are mathematically related by the Fourier transformation, and the TDEM field can thus be obtained as the Fourier transformation of FDEM data. For modeling in time-domain, we can use fast frequency-domain modeling codes and then convert the results to the time domain with a suitable numerical method. Thus, frequency-to-time transformations are of interest to EM methods, which is generally attained through fast Fourier transform. However, faster frequency-to-time transformation is required for the 3D inversion of TDEM data or for the processing of vast air-borne TDEM data. The diffusion expansion method (DEM) is one of smart frequency-to-time transformation methods. In DEM, the EM field is expanded into a sequence of diffusion functions with a known frequency dependence, but with unknown diffusion-times that must be chosen based on the data to be transformed. Especially, accuracy of DEM is sensitive to the diffusion-time. In this study, we developed a method to determine the optimum range of diffusion-time values, minimizing the RMS error of the frequency-domain data approximated by the diffusion expansion. We confirmed that this method produces accurate results over a wider time range for a homogeneous half-space and two-layered model.
Keywords
electromagnetic method; frequency-domain; time-domain; diffusion expansion method; diffusion time;
Citations & Related Records
Times Cited By KSCI : 1  (Citation Analysis)
연도 인용수 순위
1 Cho, I. K., and Lim, J. T., 2003a, Frequency sounding in smallloop EM sounding, Korean Exploration Geophysics, 6, 119-125.
2 Allegar, N., 2007, EM is becoming a major attraction, First Break, 25, 97-102.
3 Anderson, C., Long, A., Ziolkowski, A., Hobbs, B., and Wright, D., 2008, Multi-transient EM technology in practice, First Break, 26, 93-102.
4 Anderson, W. L., 1975, Improved digital filters for evaluating Fourier and Hankel transform integrals, USGS-GD-75-012.
5 Anderson, W. L., 1979, Numerical integration of related Hankel transforms of orders 0 and 1 by adaptive digital filtering, Geophysics, 44, 1287-1305.   DOI   ScienceOn
6 Balch, S. J., Boyko, W. P., and Paterson, N. R., 2003, The AeroTEM airborne electromagnetic system, The Leading Edge, 22, 562-566.   DOI
7 Cho, I. K., and Lim, J. T., 2003b, One-dimensional inversion of electromagnetic frequency sounding data, Korean Exploration Geophysics, 6, 180-186.   과학기술학회마을
8 Haines, G. V., and Jones, A. G., 1988, Logarithmic Fourier transformation, Geophysical Journal of the Royal Astronomical Society, 92, 171-178.   DOI
9 Slob, E. C., and van den Burg, P. M., 1999, Integral equation method for modeling transient diffusive electromagnetic fields, Three Dimensional Electromagnetics: SEG, 42-58.
10 Song, Y. 1992, Electromagnetic modeling of thin sheet conductor using integral equation with double Fourier transform, Ph.D thesis, Seoul National University.
11 Ward, S. H., and Hohmann, 1987, Electromagnetic theory for geophysical applications, in Electromagnetic method in Applied Geophysics: SEG, 1-132.
12 Weidelt, P., 1981, Report on dipole induction by a thin plate in a conductive half-space, Fed. Inst. Earth Sci. and Mate.
13 Tehrani, A. M., Slob, E., and Mulder, W., 2012, Quasi-analytic method for frequency to time conversion in CSEM applications, Geophysics, 77, E357-E363.   DOI