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전기비저항탐사 2차원 모델링에서 송수신 간격을 고려한 푸리에 역변환
조인기,정다빈,Cho, In-Ky,Jeong, Da-Bhin 한국지구물리·물리탐사학회 2018 지구물리와 물리탐사 Vol.21 No.1
전기탐사 2차원 모델링에서는 다수의 파수영역 전위를 계산하고 이를 푸리에 역변환하여 공간영역 전위를 계산한다. 푸리에 역변환은 여러 개의 서로 다른 파수에서의 파수영역 전위를 사용하여 수치적으로 얻어진다. 적분의 정확도를 향상시키기 위하여 파수의 크기에 따라 적분 구간을 지수 근사와 대수 근사 구간으로 분할하는 방법이 널리 사용되고 있다. 푸리에 역변환에는 크게 구간 적분법과 가우스 적분법이 사용되고 있다. 그러나 이들 방법은 송수신 간격을 고려하지 못하므로 송수신 간격에 따른 오차를 피할 수 없다. 특히 송수신 간격이 매우 작거나 클 경우 오차가 급격하게 증가하는 문제점을 가지고 있다. 이 연구에서는 송수신 간격을 고려하여 가우스 좌표값 및 가중값을 적용하는 새로운 수치 적분법을 개발하였다. 반무한 공간에 대한 수치 실험 결과, 개발된 수치 적분법은 송수신 간격에 관계없이 0.4% 이하의 정밀도를 나타내었다. In the two-dimensional (2D) modeling of electrical method, the potential in the space domain is reconstructed with the calculated potentials in the wavenumber domain using inverse Fourier transform. The inverse Fourier integral is numerically evaluated using the transformed potential at different wavenumbers. In order to improve the precision of the integration, either the logarithmic or exponential approximation has been used depending on the size of wavenumber. Two numerical methods have been generally used to evaluate the integral; interval integration and Gaussian quadrature. However, both methods do not consider the distance from the current source. Thus the resulting potential in the space domain shows some error. Especially when the distance from the current source is very small or large, the error increases abruptly and the evaluated potential becomes extremely unstable. In this study, we developed a new method to calculate the integral accurately by introducing the distance from the current source to the rescaled Gauss abscissa and weight. The numerical tests for homogeneous half-space model show that the developed method can yield the error level lower than 0.4 percent over the various distances from the current source.
터널 주변 전기비저항 토모그래피 모니터링 자료의 시간경과 역산
조인기,정재형,배규진,Cho, In-Ky,Jeong, Jae-Hyeung,Bae, Gyu-Jin 한국터널지하공간학회 2009 한국터널지하공간학회논문집 Vol.11 No.4
전기비저항 토모그래피법은 터널 주변의 물성분포나 그 변화를 탐지하는데 매우 효과적인 물리탐사 방법이다. 따라서 전기비저항 토모그래피 영상은 터널의 효과적인 유지관리를 위한 중요한 정보를 제공해 준다. 그러나 공기로 채워진 터널은 토모그래피 자료를 심하게 왜곡시키며, 이러한 현상은 송, 수신점이 터널에 근접할수록 심화된다. 또한 이러한 왜곡은 결과적으로 토모그래피 모니터링 자료의 해석에 오류를 가져오게 된다. 이런 문제점의 해결을 위하여 터널을 포함한 모델링 및 시간경과 역산법을 개발하였다. 개발된 프로그램을 사용하여 터널을 고려한 역산법이 기존의 역산법에 비하여 월등히 정밀한 영상을 제공함을 확인하였다. 또한 모니터링 자료에 시간경과 역산을 사용하여 보다 효과적으로 터널주변의 시간에 따른 전기비저항 변화대를 파악할 수 있었다. Resistivity tomography is very effective geophysical method to find out the resistivity distribution and its change in time around a tunnel. Thus, the resistivity tomogram can provide helpful information which is necessary for the effective maintenance of the tunnel. However, an air filled tunnel severely distorts tomography data, especially when the current or potential electrode is placed near the tunnel. Moreover, the distortion can often lead to misinterpretation of tomography monitoring data. To solve these problem, we developed a resistivity modeling and time-lapse inversion program which include a tunnel. In this study, using the developed program we assured that the inversion including a tunnel gives much more accurate image around a tunnel, compared with the conventional tomogram where the tunnel is not included. We also confirmed that the time-lapse inversion of resistivity monitoring data defines well resistivity changed areas around a tunnel in time.
조인기 ( In Ky Cho ),이근수 ( Keun Soo Lee ) 한국지구물리·물리탐사학회 2010 지구물리와 물리탐사 Vol.13 No.4
Resistivity data should be edited before the inversion because resistivity data are contaminated by a loi of noise. Generally, outlier or data violating pants-leg effect in dipole-dipole array were used to be nected in the apparent resistivity pseudo-section. For more precise data editing, normalized voltage curves are used. In this study, we analyzed the behavior of normalized voltage curves for pole-pole, pole-dipole and dipole-dipole arrays in the presence of three- dimensional inhomogeneities, and finally re-examined (he validity of normalized voltage curves in the editing process of resistivity data.
조인기 ( In-ky Cho ),장제훈 ( Je-hun Jang ),이명종 ( Myeong-jong Yi ),임형래 ( Hyoung-rae Rim ) 한국지구물리·물리탐사학회 2017 지구물리와 물리탐사 Vol.20 No.1
Recently, the grounded electrical-source airborne transient electromagnetic (GREATEM) system with high power source was introduced to achieve deeper investigation depth and to overcome high noise level. Although the GREATEM is a transient electromagnetic system using a long grounded wire as the transmitter, GREATEM data have been interpreted with 1D earth models because 2D or 3D modeling and inversion of vast airborne data are complicated and expensive to calculate. Generally, 1D inversion is subsequently applied to every survey point and combining 1D images together forms the stitched conductivity-depth image. However, the stitched models often result in abrupt variations in neighboring models. To overcome this problem, laterally constrained inversion (LCI) has been developed in inversion of ATEM data, which can yield layered sections with lateral smooth transitions. In this study, we analysed the GREATEM data through 1D numerical modeling for a curved grounded wire source. Furthermore, we developed a laterally constrained inversion scheme for continuous GREATEM data based on a layered earth model. All 1D data sets and models are inverted as one system, producing layered sections with lateral smooth transitions. Applying the developed LCI technique to the GREATEM data, it was confirmed that the laterally constrained inversion can provide laterally smooth model sections that reflect the layering of the survey area effectively.
조인기 ( In Ky Cho ),이근수 ( Keun Soo Lee ),강혜진 ( Hye Jin Kang ) 한국지구물리·물리탐사학회 2010 지구물리와 물리탐사 Vol.13 No.4
Resistivity method is a practical and effective geophysical technique to detect leakage zones in embankment dams. Generally, resistivity survey conducted along the crest assumes that the embankment darn has a 2D structure. However, the 3D topography of the embankment distorts significantly resistivity data measured on anywhere of the dam. This study evaluates the influence from 3D etlects created by specific dam geometry and effects of water level fluctuations through the 3D finite element modeling technique. Also, a comparison between different locations of survey line are carried out, and topographic correction technique is developed for the resistivity data obtained along the embankment dam. Furthermore, using synthetic resistivity data for an embankment dam model with leakage zone, detectability of leakage zones is estimated through 2.5D inversion.