Interpretation of Finite HMD Source EM Data using Cagniard Impedance

Cagniard 임피던스를 이용한 수평 자기쌍극자 송신원 전자탐사 자료의 해석

  • 권형석 ((주)희송지오텍) ;
  • 송윤호 (한국지질자원연구원, 탐사개발연구부) ;
  • 설순지 (부경대학교 환경탐사공학과) ;
  • 손정술 (한국지질자원연구원, 탐사개발연구부) ;
  • 서정희 (서울대학교 지구환경시스템공학부)
  • Published : 2002.05.01


We have introduced a new approach to obtain the conductivity information of subsurface using Cagniard impedance over two-dimensional (2-D) model in the presence of horizontal magnetic dipole source with the frequency range of $1\;kHz\~1\;MHz$. Firstly, we designed the method to calculate the apparent resistivity from the ratio between horizontal electric and magnetic fields, Cagniard impedance, considering the source effects when the plane wave assumption is failed in finite source EM problem, and applied it to several numerical models such as homogeneous half-space or layered-earth model. It successfully provided subsurface information even though it is still rough, while the one with plane wave assumption is hard to give useful information. Next, through analyzing Cagniard impedance and apparent resistivity considering source effect over 2-D models containing conductive- or resistive-block, we showed that the possibility of obtaining conductivities of background media and anomaly using this approach. In addition, the apparent resistivity considering source effect and phase pseudosections constructed from Cagniard impedance over the isolated conductive- and resistive block model well demonstrated outlines of anomalies and conductivity distribution even though there were some distortions came from sidelobes caused by 2-D body.