Geophysics and Geophysical Exploration (지구물리와물리탐사)

Korean Society of Earth and Exploration Geophysicists (한국지구물리·물리탐사학회)
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Laterally Constrained Inversion of GREATEM data

지상 송신원 항공 전자탐사 자료의 횡적 제한 역산

  • Cho, In-Ky (Division of Geology and Geophysics, Kangwon National University) ;
  • Jang, Je-Hun (Division of Geology and Geophysics, Kangwon National University) ;
  • Yi, Myeong-Jong (Mineral Resources Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Rim, Hyoung-Rae (Mineral Resources Division, Korea Institute of Geoscience and Mineral Resources)
  • 조인기 (강원대학교 지질.지구물리학부) ;
  • 장제훈 (강원대학교 지질.지구물리학부) ;
  • 이명종 (한국지질자원연구원 광물자원연구부) ;
  • 임형래 (한국지질자원연구원 광물자원연구부)
  • Received : 2016.11.29
  • Accepted : 2017.01.23
  • Published : 2017.02.28
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Abstract

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.

최근 도입된 지상 송신원 항공 전자탐사 시스템(grounded electrical-source airborne transient electromagnetic, GREATEM)은 신호가 강력하여 가탐심도 향상은 물론 잡음이 심한 지역에서도 적용 가능하다. 비록 GREATEM은 지상에 설치된 긴 전선을 송신원으로 사용하는 시간영역 전자탐사법이지만, 방대한 항공탐사 자료의 2차원 혹은 3차원 해석은 계산시간이 너무 많이 소요되어 실질적인 적용이 어렵기 때문에 GREATEM 탐사 자료는 주로 1차원 해석에 의존하고 있다. 일반적으로 방대한 항공 전자탐사 자료의 해석은 각 측점에서 얻어진 자료에 대한 1차원 역산 결과를 병합하여 전기비저항 2차원 단면을 작성하는 방법이 널리 사용되고 있다. 그러나 이러한 병합 단면은 전기비저항이 너무 급격하게 변하는 문제점을 보인다. 횡적 제한 역산법(laterally constrained inversion, LCI)은 이러한 문제점을 해결하기 위하여 개발되었으며, 연속성이 뛰어난 역산 단면을 제공하게 된다. 이 연구에서는 우선 수치 모델링을 통하여 곡선 전류원에 대한 GREATEM 탐사 자료의 특성을 분석하였다. 또한 GREATEM 탐사 자료에 대한 횡적 제한 역산법을 개발하였다. 이 방법은 각 측점에서 획득된 모든 1차원 자료와 층서 모델을 하나의 역산 시스템에 병합하여 처리하므로 수평적 연속성이 뛰어난 역산 단면을 제공하게 된다. 개발된 역산 알고리듬을 GREATEM 탐사 자료에 적용한 결과, 해당 지역의 층서를 효과적으로 반영하는 역산 영상을 얻을 수 있었다.

Keywords

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