• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.80-80
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• 2003

서브스톰이 진행될 때 극지방의 지자기 교란은 대류 제트 전류와 서브스톰 전류 쐐기로 구성되는 오로라 제트 전류에 기인한다. 이들은 전기장 강화를 뜻하는 AU 지수와 전기 전도도 강화를 뜻하는 AL 지수로 나타낼 수 있다. 이들 AU, AL 지수와 자기폭풍의 정도를 나타내는 Dst 지수와의 상관관계를 구해봄으로써 서브스톰이 자기폭풍의 형성에 어떻게 기여하는지 조사하였다. 이를 위하여 월별 누적 AU, 누적 │AL│ 값을 구한 뒤 월별 누적 Dst 와의 상관관계를 구하였다. 한편 IMF(Interplanetary Magnetic Field)의 남쪽 자기장 성분으로부터 지구 자기장 내에 강력한 전기장이 형성되어 자기폭풍을 형성한다는 견해가 있다. 전기장 E=V(태양풍 속도)$\times$Bs(IMF의 남쪽 자기장 성분)으로 나타낼 수 있으므로 이로부터 구한 월별 누적 전기장과 누적 Dst 값을 비교해 봄으로써 자기권 대류가 자기폭풍 형성에 어느 정도 기여하는지 조사하였다. 본 연구를 위하여 1966년부터 1987년까지 20년간의 AE(AU, AL) 지수를 이용하였으며 IMF 자료는 ACE 위성이 제공하는 행성간 자기장 자료로 1997년부터 2002년까지의 자료를 이용하였다. 본 연구의 결과는 현재 논쟁이 되고 있는 storm-substorm의 인과관계를 보다 잘 규명할 것으로 기대된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.889-893
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• 2007

본 연구에서는 도시화로 인하여 대규모 토지이용 변화가 예상되는 신도시 개발예정지구인 판교 운중천유역을 시험유역으로 선정하고, 2004년 8월부터 수문관측망을 구성하여 장기적인 수문모니터링을 수행하고 있으며, 2007년 현재 시험유역내 4개의 하천수위관측소 (판교교, 삼평교, 매송2교, 내동교), 3개의 우량관측소(매송2교, 내동교, 운중저수지), 그리고 저수지 및 용수로 수위관측소 (운중저수지) 등 총 8개 지점에 대하여 초음파 수위계 5개, 압력식 수위계 5개, 전도형 강우계 3개가 설치되어 운영중이다. 모든 자료는 10분 단위로 관측되고 있으며, 무선인터넷시스템을 통하여 모니터링 서버에 주기적으로 전송되어, 현장의 계측상황 및 장비에 대한 제어, 자료 분석 및 저장이 가능하도록 되어 있다. 관측된 모든 자료는 홈페이지(http://218.148.68.59/kict)를 통해 실시간으로 제공되고 있다.

• Geophysics and Geophysical Exploration
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• v.7 no.2
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• pp.130-135
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• 2004

This paper describes the physical properties of the factors controlling the electrical resistivity of the subsurface. Resistivities of various types of soil and rock samples saturated with sodium chloride solutions having nine different concentrations were measured, and the measured resistivities of these samples were compared with calculated resistivities obtained using the conventional empirical formulas. From the results obtained, we observed that the resistivity of the soil and rock samples increases with increasing in pore-fluids resistivity regardless of the media type. However, between 20 and 200 ohm-m, which is the normal range of resistivity of groundwater, the resistivity of the pore-fluids have little or no effect on the resistivities of the samples used. Below 10 ohm-m, the resistivities of the samples are mainly controlled by the pore-fluids, whereas, in the normal range of resistivity of groundwater, the sample resistivities are controlled by their intrinsic matrix resistivity more than by the pore-fluids resistivity. Also, the measured resistivity of rock and soil samples having more than $20\%$ clay contents showed a good agreement with the calculated resistivity using the parallel resistance model whereas, the calculated resistivities of glass beads correlate with that obtained using Archie's formula. When the pore-fluid resistivity is high, the computation of the resistivity values of the samples using the Archie's formula could not be carried out. Through this study, we were able to confirm that the tests are only applicable to the parallel resistance model considering the intrinsic matrix resistivity within the normal resistivity range of groundwater in the subsurface.

• Geophysics and Geophysical Exploration
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• v.12 no.4
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• pp.328-337
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• 2009

To investigate the relation between pore fluid conductivity and bulk resistivity of a rock sample it is assumed that electrolyte solution perfectly substitute the pore fluid that occupied the pore space within the sample in general. In this study, it is investigated that how much can the electrolyte solution substitute the pore fluid by repeating the same saturation process. Four kinds of NaCl solutions of 8, 160, 3200, 64000 ${\mu}S$/cm are used. The saturation process has repeated four times for each electrolyte in increasing conductivity order first then four times each in decreasing order. The more the saturation process repeated with the same electrolyte, the more electrolyte solution substitute the pore fluid. Geometric mean of bulk resistivity in increasing and decreasing orders with the same electrolyte solution is assumed to be mostly close to the bulk resistivity with perfect substitution. Bulk resistivity measurements for both increasing and decreasing order differs within 10% to the geometric mean when repeating the saturation process 4 times while maximum 40% difference is observed when single saturation process for each electrolyte solution with increasing order. The modified parallel resistant model can generally represent the relations between pore fluid resistivity and bulk resistivity in the experiment, but more experimental data with various rock samples with different porosity is needed to generalize the model.

• Geophysics and Geophysical Exploration
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• v.5 no.2
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• pp.108-117
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• 2002

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.

• Geophysics and Geophysical Exploration
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• v.6 no.3
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• pp.119-125
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• 2003

The small-loop electromagnetic (EM) technique has been used successfully for many geophysical investigations, particularly for shallow engineering and environmental surveys. In conventional small loop EM operating at small induction numbers, geometric sounding has been widely used because the depth of penetration of EM energy depends only on the source-receiver separation. Recently developed small loop EM system, however, measures the secondary magnetic field, $H^S$, at multiple frequencies with a fixed source-receiver separation and frequency sounding is tried actively. In this study, we analyzed the behavior of in-phase and quadrature components of ${H^S}_z$, for horizonal coplanar (HCP) configuration over two-layer models. Through this theoretical analysis, it was found that the in-phase component of ${H^S}_z$ is more suitable for frequency sounding than the quadrature component. But, the in-phase component of ${H^S}_z$ is too small to measure, especially in resistive and noisy environment like Korea. Using the fact that the quadrature component is much greater than the in-phase component and the difference of quadrature component of ${H^S}_z$ measured at two frequencies shows the same behavoir as the in-phase component, we suggested an alternative frequency sounding technique. Also, we defined an apparent conductivity, which reflects well the conductivity of subsurface layers.

• Aerospace Engineering and Technology
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• v.9 no.2
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• pp.161-167
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• 2010

CEU(Camera Electronic Unit) loaded in optical satellite for a high resolution image acquisition is composited with CC(Camera Controlloer), FPA(Focal Plane Assembly) and CEUP(CEU Power supply). EMC test and analysis results are explained in this paper. CE, CS, RE and RS test is performed in the 1st EMC test, RE, RS test which is not complied and influence considerably after shielding structure is performed in the 2nd EMC test. An effect due to the noise of CEU in the GPS/S-band receiving band is analyzed based on 2nd EMC test results. Margin more than 6dB is guaranteed when CEU is shielded.

• Geophysics and Geophysical Exploration
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• v.1 no.2
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• pp.127-135
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• 1998

The Born approximation is widely used for solving the complex scattering problems in electromagnetics. Approximating total internal electric field by the background field is reasonable for small material contrasts as long as scatterer is not too large and the frequency is not too high. However in many geophysical applications, moderate and high conductivity contrasts cause both real and imaginary part of internal electric field to differ greatly from background. In the extended Born approximation, which can improve the accuracy of Born approximation dramatically, the total electric field in the integral over the scattering volume is approximated by the background electric field projected to a depolarization tensor. The finite difference and elements methods are usually used in EM scattering problems with a 2D model and a 3D source, due to their capability for simulating complex subsurface conductivity distributions. The price paid for a 3D source is that many wavenumber domain solutions and their inverse Fourier transform must be computed. In these differential equation methods, all the area including homogeneous region should be discretized, which increases the number of nodes and matrix size. Therefore, the differential equation methods need a lot of computing time and large memory. In this study, EM modeling program for a 2D model and a 3D source is developed, which is based on the extended Born approximation. The solution is very fast and stable. Using the program, crosshole EM responses with a vertical magnetic dipole source are obtained and the results are compared with those of 3D integral equation solutions. The agreement between the integral equation solution and extended Born approximation is remarkable within the entire frequency range, but degrades with the increase of conductivity contrast between anomalous body and background medium. The extended Born approximation is accurate in the case conductivity contrast is lower than 1:10. Therefore, the location and conductivity of the anomalous body can be estimated effectively by the extended Born approximation although the quantitative estimate of conductivity is difficult for the case conductivity contrast is too high.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.83-94
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• 2012

Slopes are commonly formed both above and below roads located in mountainous terrain and along riversides. The Buk-sil site, a cut slope formed below the road, collapsed in October, 2010. A field investigation determined the causes of failure as improper drainage of valley water from the slope above the road and direct seepage of road-surface water. These factors may have accelerated the collapse via complex interaction between water and sub-surface structures such as bedding. Projection analysis of the site showed the possible involvement of plane, wedge, and toppling failure. Safety factors calculated by Limit Equilibrium Analysis for plane and wedge failure were below the standard for wet conditions. The wetness index, analyzed using topographic factors of the study area, was 9.0-10.5, which is high compared with the values calculated for nearby areas. This finding indicates a high concentration of water flow. We consider that water-flow control on the upper road is crucial for enhancing slope stability at the Buk-sil site.

• 한국지구과학회:학술대회논문집
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• 2005.09a
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• pp.124-131
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• 2005

A GDS (Geomagnetic Depth Sounding) method, one of extremely low-frequency EM methods, has been carried out to examine deep geo-electrical structures of the Korean peninsula. In this study, five additive GDS sites acquired in south-eastern area of the Korea were integrated into twelve previous GDS results. In addition, 3-D MT modeling considering the surrounding seas of the Korean peninsula was performed to evaluate sea effect at each GDS site quantitatively. As a result, Observed real induction arrows was not explained by solely sea effect, two conductive structures that are able to explain differences between observed and calculated induction arrows, was suggested. The first conductive structure is the Imjingang Belt, which is thought as a extension of Quiling-Dabie-sulu continental collision belt. The effects of the Imjingang Belt clearly appear at YIN and ICHN sites. The second one is the HCL (Highly Conductive Layer), which is considered as a conductive anomaly by mantle upwelling generated in back-basin region. The effects of the HCL are also confirmed at KZU, KMT101, 107 sites, in the south-eastern of the Korean peninsula.