• Geophysics and Geophysical Exploration
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• v.16 no.3
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• pp.163-170
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• 2013

The amplitude variation with offset of seismic data can detect fluids in the sediment and resolve the petrophysical properties of hydrocarbons in the subsurface. We analyzed and described the amplitude variation in deep sea seismic data obtained from the Ulleung Basin, East Sea. By inspecting seismic CDP-offset and CDP-angle gathers which show a bright reflection event, we decided a target zone for amplitude variation analysis. From the seismic angle gather at the middle of Ulleung Basin, we recognized amplitude increase or decrease versus offset on the intercept-gradient curve. Using the product attribute and Poisson's ratio change attribute computed in terms of intercept with gradient, the top and the base of gas saturated sediments were described. The area of amplitude variation suggestive of the presence of gas saturated sediments is shown at the depth of 3 s traveltime. Anomalous features of seismic amplitude in the Ulleung Basin were classified by the crossplot of intercept and gradient. The background trend of crossplot between intercept and gradient shows an inverse proportional relation that is common for wet sediments. Anomalous amplitudes of Class III fall into the first and the third quadrants on crossplots. We inferred regional gas/water saturated area with the horizontal dimension of 150 m in the Ulleung Basin by cross-section with respect to cross-plot anomaly.

• Geophysics and Geophysical Exploration
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• v.4 no.4
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• pp.115-123
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• 2001

The bright spot is an indicator for natural gas on seismic stack sections, but it is also shown on layers where the acoustic impedance contrast is large. In order to distinguish sharply between gas and impedance contrast we need additional detailed data processing such as velocity analysis, AVO analysis and seismic complex analysis including measures of seismic amplitude, frequency, and phase. In this study, we performed detailed velocity analysis, complex analysis and DHI (Direct Hydrocarbon Indicator) analysis which is the result of amplitude variation according to the incident angles. The seismic complex analysis gives us the geological information which depends on geophysical properties at the interest layer. For the complex analysis, we computed several seismic attributes such as the instantaneous amplitude, the first and the second derivatives of the instantaneous amplitude, the instantaneous phase, the instantaneous frequency and weighted average instantaneous frequency. Then we applied these analysis techniques to a seismic data of Korea offshore which had been logged. From the result of this data analysis, it could be said that high possibility area for gas layer detection has amplitude anomalies in the instantaneous amplitude, the instantaneous frequency and the DHI section resulting from the AVO analysis. If there are not any other anomalies in detailed data processing, it will have low possibility for gas layer detection.

• Geophysics and Geophysical Exploration
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• v.14 no.1
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• pp.25-41
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• 2011

AVO analysis was conducted on hydrocarbon-bearing structures by applying the crossplot and offset-coordinate amplitude polynomial techniques. To evaluate the applicability of the AVO analysis, it was conducted on synthetic data that were generated with an anticline model, and field data from the hydrocarbon-bearing Colony Sand bed in Canada. Analysis of synthetic data from the anticline model demonstrates that the crossplot method yields zero-offset reflection amplitude and amplitude variation with negative values for the upper interface of the hydrocarbon-bearing layer. The crossplot values are clustered in the third quadrant. The results of AVO analysis based on the coefficients of the amplitude polynomial are similar to those from the crossplots. These well correlated results of AVO analysis on field and synthetic data suggest that both methods successfully investigate the characteristics of the reflections from the upper interface of a hydrocarbon-bearing layer. Analysis based on the incident-angle equation facilitates the application of various interpretation methods. However, it requires the conversion of seismic data to an incident angle gather. By contrast, analysis using coefficients of the amplitude polynomial is cost-effective because it allows examining amplitude variation with offset without involving the conversion process. However, it warrants further investigation into versatile application. The two different techniques can be complement each other effectively as AVO-analysis tools for the detection of hydrocarbon reservoirs.

• Proceedings of the Optical Society of Korea Conference
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• 1997.08a
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• pp.61-61
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• 1997

• Journal of KSNVE
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• v.7 no.1
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• pp.20-29
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• 1997

내부공진은 2자유도계 이상의 다양한 비선형 시스템에 존재할 수 있으며 모드 사이의 진동에너지의 교환의 원인이 된다. 위에서 설명한 흡진기의 경우처럼 그 시스템의 동작에 필수적인 요소가 되기도 하며 직사각형 평판의 경우처럼 선형이론 으로는 예측불가능한 진폭변조된 진동을 유발하기도 한다. 이론적인 해석의 결과 다양한 분기와 여러가지 형태의 해를 가지며, 특히 주기적 정상해와 혼돈적인 해를 갖는 것이 밝혀졌다. 이러한 주기적 정상해는 구조물에 따라 여러 가지 형태로 나타 나며 평판의 경우는 진폭변조된 움직이는 파형으로, 본문에서는 언급하지 않았지만 현의 경우는 타원의 퀘적의 크기와 주축의 방향의 변화로 나타난다. 이러한 다양한 해들은 구조물의 종류와 형상에 따라 다른 형태로 나타나며 향후 연구의 대상이라 생각되어진다.

• Journal of Korean Ophthalmic Optics Society
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• v.12 no.4
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• pp.111-117
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• 2007

The visual evoke potential(VEP) is the effective method to diagnose and treat the amblyopia or to check the infants visual ability. In order to evaluate the changes of P100 latencies and amplitudes of VEP by intensity of illumination and refractive errors, we measured latencies and amplitudes of 41 normal adults (20/20 VA) who have no ocular diseases and neurologic diseases. The results were as follows: In the scotopic condition, the latencies were N75$75.83{\pm}3.69$ msec, P100$103.48{\pm}5.34$ msec, the P100 amplitude was $14.86{\pm}2.43$ msec, and in the photopic condition, the latencies were N75$76.71{\pm}3.11$ msec, P100$107.26{\pm}5.54$ msec and the P100 amplitude was $10.35{\pm}1.75$ msec. The latencies and amplitudes of P100 in the photopic condition had higher values than those in the scotopic condition and the measures were significantly different between the scotopic and photopic condition (p<0.01). The P100 latencies were delayed both in the scotopic and photopic condition with the refractive errors and those measures were delayed more than in the photopic condition. The P100 amplitudes in the induced myopic and hyperopic conditionsreduced than in the emmetopes in both illumination conditions. The P100 latencies and amplitudes in emmetropes showed a correlation with the induced myopic conditions in the scotopic condition. Those results showed that P100 latencies and amplitudes are dependent on the illumination conditions and refractive errors. And we suggest that those results would be useful to determine and evaluate the normal range for the person considering patients' refractive errors and illumination of the test room.

• Geophysics and Geophysical Exploration
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• v.11 no.2
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• pp.116-126
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• 2008

In gas hydrate survey, seismic amplitude and frequency characteristics play a very important role in determining whether gas hydrate exists. According to the variation of source frequency and scatterer size, we study seismic amplitude characteristics using elastic modeling applied at staggered grids. Generally speaking, scattering occurs in proportion to the square of source frequency and the scatterer volume, which has an effect on seismic amplitude. The higher source frequency is, the more scattering occurs in gas hydrate bearing zone. Therefore, BSR is hardly observed in high frequencies. On the other side, amplitude blanking zone and BSR is clearly observed in lower frequencies although the resolution is poor as a whole. Seismic reflections traveling through free-gas layer below gas hydrate bearing zone decay so severely a high frequency component that a low frequency term is dominant. Amplitude anomaly of BSR result from high acoustic impedance contrast due to free-gas, which is a very crucial factor to estimate gas hydrate bearing zone. Seismic frequency analysis is carried out using wavelet transform method that frequency component could be decomposed with time variation. In application of wavelet transform to the seismic physical experiments data, we can observe that reflections traveling through air layer, which corresponds to the free-gas layer, decay a high frequency component.

• Journal of Astronomy and Space Sciences
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• v.12 no.1
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• pp.66-77
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• 1995

It is possible to distinguish X-ray events from non X-ray events in proportional conters using the method of rise time discrimination (RTD). In order to subtract non X-ray background, we have developed a simple RTD circuit which will be applied to the proportional counter planned for a sounding rocket experiment. The entire circuit consists of two parts ; the rise time measurement circuit and the time to amplitude conversion circuit which includes the self-calibration mode. From the test with X-ray detecting system, we obtained that the background can be rejected more than 80% in the energy band 2∼12 keV. However we confirmed that the RDT method is not proper to be used for the energy range above 12kV.

• 한국해양학회지
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• v.23 no.2
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• pp.62-69
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• 1988

Analyzing short-term records of sea level data, we show that the amplitudes of diurnal tides along the southern coast of Jeju-Do are significantly larger than those along its northern coast. The amplitude-phase diagrams of $K_1$ and $O_1$ look very similar to that of $M_2$ shown by Kim and Lee (1986), indicating characteristics of the scattering of long waves by Jeju-Do.

• 한국해양학회지
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• v.28 no.3
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• pp.177-185
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• 1993

The theory for long wave scattering (Proudman, 1914: Longuet-Higgins, 1970) is applied to a tidal-frequency Kelvin wave propagating around a small cylindrical island in a shelf sea of uniform depth. The theory includes the effects of bottom friction on wave propagation. The theoretical analysis of the Kelvin wave around the island. this amplitude change results in a uniform amplitude of the total wave along the circumference of the island in an inviscid fluid, and the dynamic cause of this is explained in terms of Coriolis effects. Bottom friction attenuates the amplitude of the total wave from the frontal side of the island to the leeward side, but the amplitude variation along the coast becomes symmetric to the line connecting both idea. The phase of the scattered wave contributes to more rapid travel of the total wave in the front and leeward side than farther offshore. The effects of bottom friction on the wave phase around the island are negligible.