• The Korean Journal of Quaternary Research
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• v.21 no.2
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• pp.56-57
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• 2007

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.25 no.1
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• pp.35-46
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• 1997

Theory and observations relating to the photoelectrons are reviewed. The photoelectrons play a very important role in the photochemistry and energetics of the upper atmosphere. It is a dominant heating source for the ambient electrons in the ionosphere. This paper covers the solar EUV flux calculation, local photoelectron production rates and the two-stream approximation of the photoelectron transport in the upper atmosphere. Some data are compiled and tabulated for reference.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.191-196
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• 2007

The acoustic array waveforms are simulated in a simple borehole model for both monopole and dipole sources. The model is based on the parameters obtained by the semblance processing of field waveforms collected on the physical models whose physical parameters are known. Both the synthetic and field waveforms are compared to understand the sonic waveform as well as the source wavelet characteristics.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.293-304
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• 2017

This study was performed in order to hydrogeological analysis of aquifer, which is a necessary part for evaluating the efficiency of the combined well and open-closed loops geothermal (CWG) systems. CWG systems have been proposed for the effective utilization of geothermal energy by combining open loop geothermal systems and closed loop geothermal systems. Small aperture CWG systems and large aperture CWG systems were installed at a green house land with water curtain facilities in Chungju City. Aquifer tests include pumping tests and step-drawdown tests were conducted to analyse hydrogeological characteristics of aquifer in the study area. The transmissivity was estimated in the range of $13.49{\sim}58.99cm^2/sec$, and the storativity was estimated in the range of $1.13{\times}10^{-5}{\sim}5.20{\times}10^{-3}$. The geochemical analysis showed $Ca^{2+}$ ion and ${HCO_3}^-$ ion were dominant in groundwater. The Langelier Saturation Index and the Ryznar Stability Index showed low scaling potential of groundwater. In the analysis of vertical water temperature change, the geothermal gradient was estimated as $2.1^{\circ}C/100m$, which indicated the aquifer was enough for geothermal systems. In conclusion, groundwater is rich, can stably use geothermal heat, and it is less likely to cause deterioration of thermal energy efficiency by precipitation of carbonate minerals in study area. Therefore, the study area is suitable for installation of the combined geothermal system.

• Geophysics and Geophysical Exploration
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• v.20 no.2
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• pp.96-99
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• 2017

Virtual source data were produced by applying the seismic interferometry to the 2002 experimental seismic refraction data. Using the data, moveout velocities and effective anellipticity were experimentally computed for the crust at eight sites in the Korean peninsula. The moveout velocities of reflection events at approximate Moho depths were yielded to be $6.30{\pm}0.25km/s$ using near-offset traveltimes. Expanding the Taylor approximation to the $3^{rd}$ term for far-offset traveltimes, the effective anellipticity parameters were computed to be $0.18{\pm}0.07$ for the crust material.

• Geophysics and Geophysical Exploration
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• v.19 no.4
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• pp.236-248
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• 2016

In this review, the basic concepts of geodetic coordinate system and map projection are explained to practitioners in exploration geophysicists to enhance the understanding of geographic and projected coordinate system. The fundamental elements such as earth ellipsoid, geoid, geocentric and geodetic latitudes, rhumb line, and great circle are dealt with in detail. The geocentric and geodetic coordinate systems are also summarized neatly, together with coordinate conversion formulae. In addition, the concept and technique for datum transforms between local and world datum are presented, with special emphasis on Korean Geodetic System.

• Journal of The Korean Astronomical Society
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• v.49 no.3
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• pp.65-71
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• 2016

We obtain the first complete CCD light curves (LCs) of the contact binary AP UMi in the VRI bands and analyzed them by means of the PHOEBE code. A spotted model is applied to treat the asymmetry in the LCs. The LC morphology clearly shows the O'Connell effect and the solution shows an influence of star spots on both components. Such effect of star spots is common between the RS CVn and W UMa chromospherically active stars. Based on the obtained solution of the LCs we investigate the evolutionary state of the components and conclude that the system is a pre-intermediate contact binary (f = 0.29) with mass ratio q = 0.38, and it is an A-type W UMa system where the less massive secondary component is cooler than the more massive primary one.

• Korean Journal of Remote Sensing
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• v.37 no.1
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• pp.1-11
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• 2021

This study measures the change of ice flow velocity of David Glacier, one of the fast-moving glaciers in East Antarctica that drains through Drygalski Ice Tongue. In order to effectively observe the rapid flow velocity, we applied the offset tracking technique to Sentinel-1A SAR images obtained from 2016 to 2020 with 36-day temporal baseline. The resulting velocity maps were averaged and the two relatively fast points (A1 and A2) were selected for further time-series analysis. The flow velocity increased during the Antarctic summer (around December to March) over the four years' observation period probably due to the ice surface melting and reduced friction on the ice bottom. Bedmap2 showed that the fast flow velocities at A1 and A2 are associated with a sharp decrease in the ice surface and bottom elevation so that ice volumetric cross-section narrows down and the crevasses are being created on the ice surface. The local maxima in standard deviation of ice velocity, S1 and S2, showed random temporal fluctuation due to the rotational ice swirls causing error in offset tracking method. It is suggested that more robust offset tracking method is necessary to incorporate rotational motion.

• Transactions of the KSME C: Technology and Education
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• v.1 no.1
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• pp.33-38
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• 2013

Offshore drilling refers to a mechanical process where a wellbore is drilled through a seabed. It is typically carried out in order to explore for and subsequently extract petroleum which lies in rock formations beneath the seabed. There are many different type of facilities from which offshore drilling operations take place. These include bottom founded drilling rigs, combined drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units including semi-submersibles and drillships. These are capable of operating in water depths up to 3,000 m. In this paper, we introduce the drilling system, which is mounted on the offshore drilling facilities.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.152-157
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• 2011

The small-loop electromagnetic (EM) method is one of the rapid and non-destructive geophysical methods and has been used widely for many geophysical investigations, particularly for shallow engineering and environmental surveys. Especially in the shallow marine environment, the small-loop EM technique is very effective because of rapid and convenient data acquisition, large signal and low noise level. However, the method has been rarely applied in the very conductive marine environment since it's penetration or investigation depth might be considered too low. In this study, we demonstrated that the small-loop EM method can be effectively applied in the extremely conductive marine environment through the analysis of 1D small-loop EM data. Furthermore, we confirmed that the resistivity distribution under the sea bottom can be quantitatively predicted from the 1D inversion results of synthetic and field data.