• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.240-249
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• 2013

The seismic data quality of marine geological and engineering survey deteriorates because of the sea swell. We often conduct a marine survey when the swell height is about 1 ~ 2 m. The swell effect correction is required to enhance the horizontal continuity of seismic data and satisfy the resolution less than 1 m. We applied the swell correction to the 8 channel high-resolution airgun seismic data and 3.5 kHz subbottom profiler (SBP) data. The correct sea bottom detection is important for the swell correction. To detect the sea bottom, we used maximum amplitude of seismic signal around the expected sea bottom, and picked the first increasing point larger than threshold value related with the maximum amplitude. To find sea bottom easily in the case of the low quality data, we transformed the input data to envelope data or the cross-correlated data using the sea bottom wavelet. We averaged the picked sea bottom depths and calculated the correction values. The maximum correction of the airgun data was about 0.8 m and the maximum correction of two kinds of 3.5 kHz SBP data was 0.5 m and 2.0 m respectively. We enhanced the continuity of the subsurface layer and produced the high quality seismic section using the proper methods of swell correction.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.4
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• pp.249-258
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• 2001

Compressional wave velocity and electrical resistivity of muddy sediments in the southeastern inner shelf of Korea were studied using nine piston core samples. The acoustic and physical properties were measured with 10 cm depth interval. Sediment structures were examined by x-radiographs of the cored sediments. Subbottom profiles were obtained by a high-resolution acoustic subbottom profiler. Acoustic turbid layers are clearly seen on the profiles, and x-radiographs of the sediments showed degassying structures formed by gas escaping. On the basis of x-radiographic images, velocities, electrical resistivities and physical properties, the sediments are divided into gassy and non-gassy sediments. The presence of gas and degassying structures result in a marked variation in velocity and electrical resistivity. It can be concluded that velocity and electrical resistivity arep arameter to recognize gassy sediment. The velocity is important parameter to indicate gassy sediment.

• Journal of the Korean Geophysical Society
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• v.7 no.3
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• pp.207-215
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• 2004

As the sea connecting with the East Sea, the Sea of Okhotsk is the most potential area of gas hydrates in the world. In other to examine geophysical structures of gas hydrate-bearing sediments in the Sea of Okhotsk, the CHAOS (hydro-Carbon Hydrate Accumulation in the Okhotsk) international research expedition was carried out in August 2003. In the expedition, high-resolution seismic and geochemical survey was also conducted. Sparker seismic profiles show only diffusive high-amplitude reflections without BSRs at BSR depth. It means that BSR appears to be completely different images on seismic profiles obtained using different frequencies. Many gas chimneys rise up from BSR depth to seafloor. The chimneys can be divided into two groups with different seismic characteristics; wipe-out (WO) and enhanced reflection (ER) chimneys. Different seismic responses in the chimneys would be caused by amount of gas and gas hydrates filling in the chimneys. In hydroacoustic data, a lot of gas flares rise up several hundreds meters from seafloor to the water column. All flares took placed at the depths within gas hydrate stability zone. It is interpreted that gas hydrate-bearing sediments with low porosity and permeability due to gas hydrate filling in the pore space make good pipe around gas chimneys in which gas is migrating up without loss of amount. Therefore, large-scale gas flare at the site on gas chimney releases into the water column.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.192-198
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• 2009

Side scan sonar and SBP (sub-bottom profiler) play a very important role in the survey for seafloor imaging and sub-bottom profiling. In this study, we have acquired side scan sonar and SBP data from the artificial reef area. We applied digital image processing techniques to side scan sonar data in order to improve an image quality. For the enhancement of data quality and image resolution, we applied the typical seismic data processing sequence including gain recovery, muting, spectrum analysis, predictive deconvolution, migration to SBP data. We could easily estimate if artificial reef structures were settled properly and their distribution on the seafloor from the integrated interpretation of side scan sonar and SBP data. From the sampling analysis of seabed sediments, texture filtering of side scan sonar data and SBP data interpretation, we could evaluate the sediment type, distribution and thickness of seafloor sediments in detail.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.537-543
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• 2008

To effectively delineate the foundation of stone relics by GPR and seismic refraction methods, a geological engineering model was constructed with alternating layer of soil and gravel to a depth of 3 m. This study was aimed at mapping the boundaries of model ground structure and interfaces of alternating layer using the various frequency antenna in GPR survey and seismic velocities. Compared to the resolution from the high frequency antenna, the image resolution from the survey using 100 Hz antenna is the lower, but with the deeper image coverage. On the contrast, the deeper structure was not mapped in the higher frequency data due to higher absorption effect, but the shallow layered zone was distinctively resolved. Therefore subsurface images were effectively provided by integrating the data with 100 MHz and 450 MHz antennas for the deep and shallow structures, respectively. Regarding the seismic refraction data, the boundaries of the model and interface of the alternating layers were not successfully mapped due to the limit of the survey length. However, the equivalent contours of low velocity extended deep as considerable velocity contrasts with surrounding ground.

• Journal of the Korean Association of Geographic Information Studies
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• v.9 no.3
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• pp.107-122
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• 2006

The main objective of this study is to develop a web-based Geographic Information System (GIS) application, IGIS(Integrated Groundwater Information Service System), for efficient management of groundwater data. This integrated system includes various groundwater measurements, monitoring data, well data, hydrogeochemical data, hydrogeological maps and diversely analyzed results including time series analysis data for water levels and quality. It will be used efficiently for local government officers to manage groundwater within their districts and also for drillers and investigators to develop wells and assess groundwater conditions. This web-based GIS system was implemented firstly for Cheonan and Daegu city. As a result, the system makes the efficient management, distribution and utilization of groundwater data possible by web-based GIS technology.

• The Journal of the Acoustical Society of Korea
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• v.15 no.1
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• pp.71-80
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• 1996

Characteristics of sleeve-gun arrays installed on the R/V Onnuri were analyzed and compared with survey data. In the case of cluster array, the beam width in the frequency range up to 814Hz is constant as $179.5^{\circ}$, and rapidly narrows in the frequency range of 814-1631Hz. However, in the case of long and wide arrays, as the frequency increases, the beamwidth decreases. The optimal frequency is 69Hz. the main lobe of vertical inclination has its maximum amplitude at phase angle $0^{\circ}$. The optimal frequency of cluster array which produces little side lobe is less than 1631Hz, and those of long and wide arrays are less than 108Hz. As a result, the cluster array produces a good source for high-resolution seismic survey, while the long and wide arrays are suitable for the survey of deep structures. The final high-resolution seismic section with cluster array was compared with that of long and wide arrays.

• Geophysics and Geophysical Exploration
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• v.14 no.4
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• pp.289-297
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• 2011

Chirp sub-bottom profilers (SBP) data are comparatively higher-resolution data than other seismic data and it's raw signal can be used as a final section after conducting basic filtering. However, Chirp SBP signal has possibility to include various noise in high-frequency band and to provide the distorted image for the complex geological structure in time domain. This study aims at the goal to establish the workflow of Chirp SBP data processing for enhanced image and to analyze the proper parameters for the domestic continental shelf. After pre-processing, we include the dynamic S/N filtering to eliminate the high-frequency component noise, the dip scan stack to enhance the continuity of reflection events and finally the post-stack depth migration to correct the distorted structure on the time domain sections. We demonstrated our workflow on the data acquired by domestically widely used equipments and then we could obtain the improved seismic sections of depth domain. This workflow seems to provide the proper seismic section to interpretation when applied to data processing of Chirp SBP that are largely used for domestic acquisition.

• Economic and Environmental Geology
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• v.42 no.6
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• pp.627-634
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• 2009

Redefining the difference among the Yamaguchi's 'so-called Yeoncheon system,' north Korean's 'Rimjin System' and Yeoncheon Group of national geological map, authors tried to avoid a possible misunderstanding of concept between Yeoncheon Group and Imjingang fold Belt. As a tool of preliminary geological mapping and or N-S reconnaissance of the whole Yeoncheon Group, an interpretation technique of satellite image from various angles has been applied to understand the geometrical attitude of strike and dip of random spot, and a further concept like as cross section.

• Proceedings of the Korea Society of Environmental Biology Conference
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• 2002.11a
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• pp.41-45
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• 2002

광양만의 지형변화 및 퇴적환경발달양상에 대해 표층퇴적물과 지층탐사자료를 이용하여 연구하였다. 광양만 해역은 1970년대이후 광양만 개발에 따라 해안선 및 해저지형이 급격한 변화를 겪어왔다. 광양만의 면적은 개발이전보다 25%정도 감소하였다. 해안선 변형은 공단건설을 위한 해안매립공사로 인해 그리고 해저지형변화는 대형선박들의 안전항로개발을 위한 해저퇴적물의 준설 등에 의해 발생하고 있다. 표층퇴적물는 점토질 퇴적물 묘도서측 및 여수해만의 외해지역에 주로 분포하고, 사질 퇴적물은 섬진강하구와 수로에 분포하고 있다. 표층퇴적물의 유기물 함량은 퇴적물의 특성을 반영하며, 특히 점토질퇴적물에 다량으로 포함하고 있다. 탄성파 단면도상에서 기반암위에 Unit II와 Unit I가 분포하며, 하부 Unit II는 홀로세 이전의 하천환경 퇴적층으로 판단되며, 홀로세 Unit I 퇴적층은 섬진강하구에서 외해를 향해 전진퇴적양상의 쐐기형태를 보인다. 이 층은 섬진강에서 유출된 퇴적물이 델타환경을 이루면서 형성된 퇴적층서로 해석된다. Unit I 퇴적층내에 천부가스층이 광범위하게 분포한다. 천부가스는 광양만의 생태환경에 영향을 미칠 것으로 판단된다. 광양만 주변의 재발에 따른 해안 및 해저지형의 급격한 변형은 퇴적환경 및 해양환경에 변화를 야기할 것으로 예상된다. 특히 섬진강 하구지역의 광양제철소 건설은 섬진강에서 장양만으로 유입되는 퇴적물의 퇴적작용의 커다란 영향을 미칠 것으로 판단된다.