• 한국지구과학회지
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• 제23권1호
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• pp.15-29
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• 2002

Bayesian inversion for gravity and resistivity data was performed to investigate the cavity structure appearing as a lava tunnel in Cheju Island, Korea. Dipole-dipole DC resistivity data were proposed for a prior information of gravity data and we applied the geostatistical techniques such as kriging and simulation algorithms to provide a prior model information and covariance matrix in data domain. The inverted resistivity section gave the indicator variogram modeling for each threshold and it provided spatial uncertainty to give a prior PDF by sequential indicator simulations. We also presented a more objective way to make data covariance matrix that reflects the state of the achieved field data by geostatistical technique, cross-validation. Then Gaussian approximation was adopted for the inference of characteristics of the marginal distributions of model parameters and Broyden update for simple calculation of sensitivity matrix and SVD was applied. Generally cavity investigation by geophysical exploration is difficult and success is hard to be achieved. However, this exotic multiple interpretations showed remarkable improvement and stability for interpretation when compared to data-fit alone results, and suggested the possibility of diverse application for Bayesian inversion in geophysical inverse problem.

• 한국지반공학회논문집
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• 제18권6호
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• pp.83-101
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• 2002

탄성파는 지표면에 가까운 흙에 관한 중요한 정보를 공급한다. 흙특성 파악에 물리탐사기법의 원활한 적용을 위하여 탄성파인자와 흙특성과의 관계를 고찰하였다. 적용 예로서, 비포화토의 거동 및 특성을 전단파 시험을 통하여 알아보았다. 포화시료를 건조하면서 밴더엘리먼트를 사용하여 미소변형률 전단강성을 연속적으로 측정하였다. 비포화토에서는 모세관현상, 이온공유에 의한 접착, 세립자 이동에 의한 강화효과, 염 침전에 의한 시멘트결합과 같은 입자간 힘의 변화가 강성의 변화에 직접적으로 영향을 끼치는 것으로 나타났다. 비포화토의 시료를 교란함으로써 메니스커스의 회복에 대한 연구를 수행하였고, 비포화토에서 일어나는 여러 가지 현상들을 제시하였다.

• IUGG한국위원회:학술대회논문집
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• IUGG한국위원회 2003년도 정기총회 및 학술발표회
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• pp.18-18
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• 2003

Three-dimensional finite-difference simulation of earthquake ground motion is performed using a locally variable time-step (LVTS) scheme matching with discontinuous grids. Discontinuous grids in three directions and extension of the discontinuous grids' boundary to the free-surface in the LVTS scheme minimize the cost of both the computational memory and the CPU time for models like the localized sedimentary basin. A simplified model of sedimentary basin is dealt to show the feasibility and efficiency of the LVTS scheme. The basin parameters are examined to understand the main characteristics on ground-motion response in the basin. The results show that the seismic energy is concentrated on a marginal area of the basin far from the source. This focusing effect is mainly due to the constructive interference of the direct S-wave with the basin-edge induced surface waves. The ground-motion amplification over the deepest part of the basin is relatively lower than that above the shallow basin edge. Therefore the ground-motion amplification may be more related to the source azimuth or the direction of the incident waves into the basin rather than the depth of it.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제22권1호
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• pp.1.2-5
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• 1994

Ionospheric sounding experiments have been conducted at RRL (Radio Research Laboratory), Ministry of Communications, using Digisonde 256 since its installation in 1990. Routine observations of the vertical sounding are carried out 48 times (or 39 times) a day, at every 24 hour. In addition, we also made oblique sounding experiments to obtain the real time data of Maximum Usable Frequency (MUF) and detect the anomalous HF propagation, as a part of the joint study between RRL and CRL (Communications Research Laboratory) of Japan. The two stations involved in the study were Anyang (RRL, Korea) and Kokubunji (CRL, Japan). The ionosondes used in both stations were Digisonde 256, developed by ULCAR (University of Lowell, Center for Atmospheric Research), U. S. A. , and the synchronization of time was accomplished with the help of GPS receiver. During most part of the experiments RRL transmitted non-modulated pulses, and CRL received them. The experiment was scheduled from October 25 through October 29, 1993. However, the ionosphere was not developed well enough to conduct the experiment with pre-set operation parameters. The experiment became successful (from 0500 UT to 0800 UT, October 29) only after the operation parameters had been changed, and the continuous ionograms were obtained by CRL at 0718 UT and 0733 UT in October 29, 1993. We believe this type of experiment will ensure the qualitative enhancement of solar-terrestrial physics research and a routine observation of the oblique ionospheric sounding. In this report, we present the results of the fore-mentioned oblique sounding as well as the vertical sounding results obtained by Digisonde 256 at Anyang station of RRL.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제23권1호
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• pp.34-38
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• 1995

A diagnostic study on the summertime air mass thunderstorms occurring in the middle region of South Korea was made by analyzing the data of surface and upper air observations as well as the surface and upper level weather charts. The key parameters used in the present study are the amount of precipitable water below 850 hPa level, the vertical profiles of water vapor content and wind, and both the temperature difference and the equivalent potential temperature difference between 850 hPa and 700 hPa levels. It is found from this study that the summertime air mass thunderstorms in the middle region of South Korea can be classified into two distinct types, type I and type II. The thunderstorms of type I occur under the atmospheric conditions of high moisture content, low vertical wind shear in low levels, and conditional instability between 850 hPa and 700 hPa levels. On the other hand, the thunderstorms of type II occur under the atmospheric conditions of less moisture content, higher wind shear and conditional instability. Furthermore, our study suggests that atmospheric instability and the amount of water vapor below 850 hPa level are complementary in the development of air mass thunderstorms. The complementary nature between these two parameters may be an explanation for the thunderstorm development in the areas of low atmospheric water vapor content such as the plains of eastern Colorado.

• Structural Engineering and Mechanics
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• 제67권1호
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• pp.53-67
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• 2018

The changes of parameters of pressure and velocity of propagation of elastic pressure and shear waves in uniformly deformed solid compressible media are studied within the nonclassically linearized approach (NLA) of nonlinear elastodynamics to create a new theoretical basis of the geomechanical interpretation of various groups of geophysical observational and experimental data. The cases of small and large deformations are considered while their describing by various elastic potentials, i.e., problems considering the physical and geometric nonlinearity. Convenient analytical formulae are obtained to calculate the indicated parameters in the deformed isotropic media within the nonclassical linear and nonlinear solution in the NLA. Specific numerical experiments are conducted in case of overall compression of various materials. It is shown that the method (generally accepted in the studies of mechanics of standard constructional materials) of additional linearization (relative to the pressure parameter) in the basic correlations of the NLA introduces substantial quantitative and qualitative errors into the results at significant preliminary deformations. The influences of the physical and geometric nonlinearity on the studied characteristics of the medium are large in various materials and differ qualitatively. The contribution of nonlinear components to the values of the considered parameters prevails over linear components at large deformations. When certain critical values of compression deformations in the medium are achieved, elastic waves with actual velocity cannot propagate in it. The values of the critical deformations for pressure and shear waves differ within different elastic potentials and variants of the theory of initial deformations.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.393-396
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• 2004

In this paper, multifrequency, polarimetric SAR data acquired during the first SIR-C/XSAR mission over the Seoul and Gyunggi-do (Korea) test sites are analyzed. The main objective of the study is to assess the possibility of extracting relevant information about surface properties for geophysical applications using polarimetry. This study analyses the characteristics of polarization responses and polarimetric parameters to conditions present in urban, river, agricultural, and forested areas. Results indicate that the dominant scattering property from these fields varies depending on the land cover types. The polarization response graphs and the backscattering coefficients associated with the polarimetric parameters are also useful in characterizing these cover types.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.1023-1026
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• 2006

As it was shown recently, climate changes in Antarctica resulted in interannual trends of some climatic parameters like sea level pressure, surface air temperature, ice thickness and others. These tendencies have effect on the Southern Ocean meteorological and hydrological regime. The following remote sensing data: AVHRR MCSST data, satellite altimetry data (merged data of mission ERS-2, TOPEX/Poseidon, Jason-1, ENVISAT, GFO-1) are used to analyse the interannual and/or climatic tendency of sea surface temperature (SST) and sea level anomaly (SLA). According to the obtained results, SST has negative trend $-0.02{\pm}0.003^{\circ}C/yr$ for 24-yr record (1982-2005) and SLA has positive trend $0.01{\pm}0.005$ cm/yr for 24-yr record (1982-2005) and $0.24{\pm}0.026$ cm/yr for 12-yr record (1993-2005). However in some areas (for example, Pacific-Antarctic Ridge) SST and SLA tendencies are stronger $-0.065{\pm}0.007^{\circ}C/yr$ and $-0.21{\pm}0.05$ cm/yr, respectively.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 1999년도 제2회 학술발표회
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• pp.48-64
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• 1999

탄성파 굴절법 탐사를 이용한 지반조사시 탐사 결과로부터 표토층 및 풍화대 깊이, 연암 또는 기반암의 심도, 단층 파쇄대나 연약지반의 위치 및 규모, 지질경계 등을 파악, 지하 속도분포를 도출함으로서 Rippability 등 지반 공학적 특성의 정량적 평가가 가능하다. 양질의 자료 취득을 위하여는 조사목적과 탐사심도에 맞는 측선길이 및 배치, 수진점과 진원점 간격 및 배치, 지형기복 여부 등 현장조사 파라미터의 설정이 중요하다. 택지개발 지역의 절토 사면부에서는 수진점 간격을 3${\~}$5m, 터널 지역에서는 5${\~}$10m 정도가 적합하며 측선의 배열은 주측선과 주요 지점에서 이에 사교하는 부측선 배치가 필요하다. 굴절법 토모그라피 해석기법의 적용시, 조사장비의 가용 채널 수에 1/2 이상의 진원점으로부터 자료를 취득해야 자료처리시 지형의 영향을 받지 않는다. 편마암 지대인 절토사면부에서 시추자료와 비교하여 탄성파 속도에 의한 지반분류는 토사 700m/s 이하, 풍화암 700${\~}$l,200m/s, 연암 1,200${\~}$l,800ni/s이고 굴삭난이도(리퍼빌리티)는 리핑암 700~l,200m/s, 발파암 1,800m/s 이상으로 나타났다. 터널 지역에서는 전통적인 해석기법을 적용하였으며 터널 계획고와 탄성파 속도 1,200m/s${\~}$l,900m/s에 해당되는 연암층과 접하는 구간에서는 지질조사 및 비저항 탐사결과로부터 해석된 3개의 지질 구조선과 만나고 있으므로 터널 설계/시공 시 이의 결과 반영이 필요하다.

• 지구물리와물리탐사
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• 제9권4호
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• pp.299-303
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• 2006

지질잡음, 특히 이들이 천부에 위치할 경우 물리탐사자료의 해석에 상당한 문제가 된다. 따라서 이들 지질잡음을 효과적으로 억제해야만 조사지역내의 주된 이상체를 정확하게 탐지해 낼 수 있다. 물리탐사자료의 역산에서 천부에 존재하는 물성대비가 크지 않은 소규모 이상체는 지질잡음의 하나로 생각할 수 있다. 현재 물리탐사 자료의 역산에는 평활화 제한 최소자승법이 널리 사용되고 있다. 이 방법은 물성대비가 큰 모델변수에는 강한 제한을 가하고, 작은 모델변수에는 약한 제한을 가한다. 따라서 천부에 존재하는 소규모 이상체(지질잡음)를 제거하는 데는 한계가 있다. 본 연구에서는 큰 모델변수에는 작은 제한을, 작은 모델변수에는 강한 제한을 가하는 새로운 MTE 역산법을 개발하였으며, 이 방법은 천부의 소규모 이상체의 억제에 효과적이다. 개발된 역산 방법을 소형루프 전자탐사자료의 2.5차원 역산에 적용한 결과 천부의 소규모 이상체를 효과적으로 억제하고 주 대상체를 보다 선명하게 나타내는 영상을 얻을 수 있었다.