• Geophysics and Geophysical Exploration
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• v.25 no.1
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• pp.26-37
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• 2022

Recently, multiple methods using small aircraft for geophysical exploration have been suggested as a result of the development of information and communication technology. In this study, we introduce the hybrid unmanned aircraft electromagnetic system of the Korea Institute of Geosciences and Mineral resources, which is under development. Additionally, data processing and interpretation methods are suggested via the analysis of datasets obtained using the system under development to verify the system. Because the system uses a three-component receiver hanging from a drone, the effects of rotation on the obtained data are significant and were therefore corrected using a rotation matrix. During the survey, the heights of the source and the receiver and their offsets vary in real time and the measured data are contaminated with noise. The noise makes it difficult to interpret the data using the conventional method. Therefore, we developed a recurrent neural network (RNN) model to enable rapid predictions of the apparent resistivity using magnetic field data. Field data noise is included in the training datasets of the RNN model to improve its performance on noise-contaminated field data. Compared with the results of the electrical resistivity survey, the trained RNN model predicted similar apparent resistivities for the test field dataset.

• Economic and Environmental Geology
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• v.57 no.1
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• pp.51-71
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• 2024

Seismic exploration is one of the widely used geophysical exploration methods with various applications such as resource development, geotechnical investigation, and subsurface monitoring. It is essential for interpreting the geological characteristics of subsurface by providing accurate images of stratum structures. Typically, geological features are interpreted by visually analyzing seismic sections. However, recently, quantitative analysis of seismic data has been extensively researched to accurately extract and interpret target geological features. Seismic attribute analysis can provide quantitative information for geological interpretation based on seismic data. Therefore, it is widely used in various fields, including the analysis of oil and gas reservoirs, investigation of fault and fracture, and assessment of shallow gas distributions. However, seismic attribute analysis is sensitive to noise within the seismic data, thus additional noise attenuation is required to enhance the accuracy of the seismic attribute analysis. In this study, four kinds of seismic noise attenuation methods are applied and compared to mitigate random noise of poststack seismic data and enhance the attribute analysis results. FX deconvolution, DSMF, Noise2Noise, and DnCNN are applied to the Youngil Bay high-resolution seismic data to remove seismic random noise. Energy, sweetness, and similarity attributes are calculated from noise-removed seismic data. Subsequently, the characteristics of each noise attenuation method, noise removal results, and seismic attribute analysis results are qualitatively and quantitatively analyzed. Based on the advantages and disadvantages of each noise attenuation method and the characteristics of each seismic attribute analysis, we propose a suitable noise attenuation method to improve the result of seismic attribute analysis.

• Journal of the Korean Geophysical Society
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• v.5 no.4
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• pp.321-328
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• 2002

Difficulties encountered in downhole S-wave (shear wave) surveys include the precise determination of shear wave travel times and determination of geophone orientation relative to the direction of polarization caused by the seismic source. In this study an S-wave enhancing and a principal component analysis method were adopted as a tool for determination of S-wave arrivals and the direction of polarization from downhole S-wave survey data. An S-wave enhancing method can almost double the amplitudes of S-waves, and the angle between direction of polarization and a geophone axis can be obtained by a principal component analysis. Once the angle is obtained data recorded by two horizontal geophones are transformed to principal axes, yielding so called scores. The scores gathered along depth are all in-phase, consequently, the accuracy of S-wave arrival picking could be remarkably improved. Applying this processing method to the field data reveals that the test site consists of a layered ground earth structure.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.47.2-47.2
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• 2015

At local, galaxy properties are well known to be clearly different in different environments. However, it is still an open question how this environment-dependent trend has been shaped. In this presentation, we will show the results of our investigation about the evolution of star-formation properties of galaxies over a wide redshift range, from z~2 to z~0.5, focusing its dependence on their stellar mass and environment. In the UKIDSS/UDS region, we estimated photometric redshifts and stellar population properties, such as stellar masses and star-formation rates, using the deep optical and near-infrared data available in this field. Then, we identified galaxy cluster candidates at z~0.5-2. Through the analysis and comparison of star-formation (SF) properties of galaxies in clusters and in field, we found interesting results regarding the evolution of SF properties of galaxies: (1) regardless of redshifts, stellar mass is a key parameter controlling quenching of star formation in galaxies; (2) At z<1, environmental effects become important at quenching star formation regardless of stellar mass of galaxies; and (3) However, the result of the environmental quenching is prominent only for low mass galaxies (M* < $10^{10}M_{\odot}$) since the star formation in most of high mass galaxies are already quenched at z > 1.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.35-41
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• 2003

Rock mass characterization is an integral part of rock engineering design. Much of the information for rock mass characterization comes from field fracture mapping and data collecting. This paper describes two technologies that can be used to assist with the field mapping and data collecting activities associated with rock mass characterization: digital image processing and 3D laserscanning. The basis for these techniques is described, as well as the results of field case studies and an analysis of the error in estimating fracture orientation.

• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.35-39
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• 2003

A software to visualize and analyse 3-D seismic data is developed using OpenGL, one of the most popular 3-D graphic library, under the PC and Windows platform. The software can visualize the data as volume and slices, whose color distribution is specified by a special dialog box that can pick a color in RGB or HSV format. The dialog box can also designate opacity values so that several 3-D objects can be displayed superimposed each other. Horizon picking is implemented very easily with this software thanks to the guided picking method. The picked points from a horizon will compose a set of points, mesh, and a surface, which can be viewed and analysed in three dimensions.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2003.10a
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• pp.1-8
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• 2003

Acoustics is widely used in marine and inland fisheries research and management. In June 2002 ICES (Council for the Exploration of the Sea) held a symposium titled “Acoustics in Fisheries and Aquatic Ecology” in Montpellier, France. There were several topics to be presented such as ecology marine waters, combination of methods, target strength (TS) method and results, TS modeling, survey design, behavior, avoidance, technology, and identification. (omitted)

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.37-43
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• 2007

The MH21 Research Consortium has conducted a high-resolution 3D seismic survey and a seafloor geochemical survey, to explore methane hydrate reservoirs in the eastern Nankai Trough, offshore Japan. Excellent geological information about shallow formations was obtained from the high-resolution 3D seismic survey, which was designed to image the shallow formations where methane hydrates exist. The information is useful in constructing a geological and geochemical model, and especially to understand the complex geology of seafloor, including geochemical manifestations and the structure of migration conduits for methane gas or methane-bearing fluid. By comparing methane seep sites observed by submersibles with seismic sections, some significant relationships between methane hydrate reservoirs, free gas accumulations below the seafloor, and seafloor manifestations are recognised. Bathymetric charts and seafloor reflection amplitude maps, constructed from seismic reflections from the seafloor, are also useful in understanding the relationships over a vast area. A new geochemical seafloor survey targeted by these maps is required. The relationships between methane hydrate reservoirs and seafloor manifestations are becoming clearer from interpretation of high-resolution 3D seismic data. The MH21 Research Consortium will continue to conduct seafloor geochemical surveys based on the geological and geochemical model constructed from high-resolution 3D seismic data analysis. In this paper, we introduce a basis for exploration of methane hydrate reservoirs in Japan by fusion of 3D seismic exploration and seafloor geochemical surveys.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.225-233
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• 2013

The accuracy of the automatic NMO velocity analysis, which is used for an effective and objective NMO velocity analysis, is highly affected by the velocity resolution of the velocity spectrum. In this study, we have developed an automatic NMO velocity algorithm, where the velocity spectra are created using high-resolution bootstrapped differential semblance (BDS), and the velocity analysis on CMP gathers is performed in parallel with MPI. We also compared the velocity models from the developed automatic NMO velocity algorithm with high-resolution BDS to those from BDS. To verify the developed automatic velocity analysis module we created synthetic seismic data from a velocity model including horizon layers. We confirmed that the developed automatic velocity analysis module estimated velocity more accurately. In addition, NMO velocity which yielded a CMP stacked section, where the coherency of the events were improved, was estimated when the developed module was applied to a marine field data set.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.296-301
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• 2021

GPR is used for non-destructive investigations, ground investigations, and underground facilities exploration at construction sites. In this study, the applicability to GPR exploration of water pipes linked to Network RTK was presented. Data on the water supply pipes in the study site were acquired using GPR, and the location and depth of buried water pipes could be measured. The accuracy was evaluated from the GNSS observation performance and showed a deviation of -0.16m ~ 0.15m. This satisfied the equipment performance of the public survey work regulation, suggesting that the exploration of water pipes using GPR is possible. Because GPR does not require grounding installation, as in conventional metal pipe detectors, it will increase the efficiency of work for underground facility exploration. Exploration using GPR can acquire the location and depth of metallic and non-metallic underground facilities, so it can be utilized in the construction of a GIS system. If a comparison of the exploration characteristics is carried out, it will be possible to present various uses of underground facility exploration using GPR.