• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.353-360
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• 2007

We practiced fresh water injection test to identify its applibility as a method of seawater intrusion mitigation technique, and monitored the change of borehole fluid conductivity and the behavior of injected fresh water using borehole multichannel electrical conductivity monitoring and well-logging, and DC resistivity and SP monitoring at the surface. Well-logging and multichannel EC monitoring showed the decrease of fluid conductivity due to fresh water injection. We note that such an injection effect lasts more than several month which means the applibility of fresh water injection as a seawater intrusion control technique. Although SP monitoring did not show meaningful results because of weather condition during monitoring and the defects of electrodes due to long operation time, DC resistivity monitoring showed its effectiveness and applicability as a monitoring and assessment techniques of injection test by means of imaging the behavior and the front of fresh water body in terms of the increase of resistivity with reasonable resolution. In conclusion, we note that geophysical techniques can be an effective method of monitoring and evaluation of fresh water injection test, and expect that fresh water injection may be an practical method for the mitigation of seawater intrusion when applied with optimal design of injection well distribution and injection rate based on geophysical evaluation.

• Geophysics and Geophysical Exploration
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• v.14 no.3
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• pp.220-226
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• 2011

In the elastic wave equations, both horizontal and vertical displacements are defined. Since we can measure both the horizontal and vertical displacements in field acquisition, these displacements compose a displacement vector. In this study, we propose a frequency-domain elastic waveform inversion technique taking advantage of the magnitudes of displacement vectors to define objective function. When we apply this displacement-vector objective function to the frequency-domain waveform inversion, the inversion process naturally incorporates the back-propagation algorithm. Through the inversion examples with the Marmousi model and the SEG/EAGE salt model, we could note that the RMS error of the solution obtained by our algorithm decreased more stably than that of the conventional method. Particularly, the density of the Marmousi model and the low-velocity sub-salt zone of the SEG/EAGE salt model were successfully recovered. Since the gradient direction obtained from the proposed objective function is numerically unstable, we need additional study to stabilize the gradient direction. In order to perform the waveform inversion using the displacementvector objective function, it is necessary to acquire multi-component data. Hence, more rigorous study should be continued for the multi-component land acquisition or OBC (Ocean Bottom Cable) multi-component survey.

• Geophysics and Geophysical Exploration
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• v.25 no.3
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• pp.109-119
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• 2022

The computational efficiency of reverse time migration (RTM) based on numerical modeling is not secured due to the high-frequency band of several hundred Hz or higher for data acquired through a three-dimensional (3D) ultra-high-resolution (UHR) seismic survey. Therefore, this study develops an RTM program to derive high-quality 3D geological structures using UHR seismic data. In the traditional 3D RTM program, an excitation amplitude technique that stores only the maximum amplitude of the source wavefield and a domain-limiting technique that minimizes the modeling area where the source and receivers are located were used to significantly reduce memory usage and calculation time. The program developed through this study successfully derived a 3D migration image with a horizontal grid size of 1 m for the 3D UHR seismic survey data obtained from the Korea Institute of Geoscience and Mineral Resources in 2019, and geological analysis was conducted.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.155-160
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• 2006

In this paper, we propose a spatial filtering scheme using factorial kriging, one of geostatistical filtering methodin order to separate regional and residual gravity anomaly. This scheme is based on the assumption that regional anomalies have longer distance relation and residual anomalies have effected on smaller range. We decomposed gravity anomalies intotwo variogram models with long and short effectiveranges by means of factorial kriging. And decomposed variogram models produced the regional and residual anomalies. This algorithm was examined using by a synthetic gravity data, and applied to a real microgravity data to figure out abandoned mineshaft.

• Geophysics and Geophysical Exploration
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• v.21 no.3
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• pp.183-197
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• 2018

In the delineation of geological structures using seismic exploration, it is very important to improve resolution of seismic data as well as accurate velocity model building and subsurface imaging. The resolution of seismic data can be enhanced by employing high-frequency energy sources or by applying deconvolution techniques in data processing. In marine seismic exploration, however, the main reason for degradation of resolution is the loss of specific frequency components due to ghosts. If we remove the ghosts, we can obtain broadband seismic data by avoiding frequency loss, and thus providing high-resolution subsurface images. Although ghosts can be properly filtered out in the data processing step, more effective broadband seismic technologies have been developing through the evolution of seismic instruments and the innovation of survey design. Overseas exploration companies developed brand-new configurations of receivers such as over/under streamer and variable-depth streamer, or ghost removal techniques using dual-sensor streamer to serve high-resolution imaging technologies. Unfortunately, neither broadband seismic instrument nor processing technique has been studied in Korea. In this paper, we introduce fundamental theories and current status of broadband seismic technologies to assist domestic researchers to study those technologies.

• Journal of the Korean Geophysical Society
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• v.7 no.1
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• pp.51-60
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• 2004

Time pasages could deteriorate the flow ability and hold the flow in the water distribution facilities because of their erosion and breakdown. It is necessary that the study to determine the optimal change time and the improvement plan for the continuous management using optimization methods or decision support systems. But, the present study tendency only aware the changes of hydraulic characteristics without industrial management plans. This study shows the pipe replacement program in these two concepts and the elementary process to apply it to Daejeon city.

• Journal of the Korean Geophysical Society
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• v.4 no.3
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• pp.163-173
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• 2001

This paper deals with scheduling problems which are the most important subtask in High-Level Synthesis. Especially, we have concentrated our attentions on the data-path scheduling which can get the structural informaion trom the behavioral algorithm as a first step in synthesis procedure. Suggest Forward scheduling methode is executed the ASAP and ALAP scheduling to use the fifth - order elliptic wave filter of a standard benchmark moedl, and then it is drawing up T.N matrix table by the number resource and control-step, using the table extract of the simple than down-limit value of the control-step for the number of given resource th use this table. All of existing list scheduling techniques determine the priority function first, and then do the operation scheduling, But, the suggested forward scheduling technique does the schedule first, and determines the priority functions if needed in scheduling process.

• Journal of the Korean Geophysical Society
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• v.4 no.3
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• pp.205-217
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• 2001

Time pasges could deteriorate the flow ability and hold the folw in the water distribution facilities because of their erosion and breakdown. It is necessary that the study to determine the optimal change time and the improvement plan for the continuous management using optimization methods or decision support systems. But, the present study tendency only aware the changes of hydraulie characteristics without industrial management plans. This study shows the pipe replacement program in these two concepts and the elementary process to apply it to Daejeon city.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.77-84
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• 2009

Ground penetrating radar (GPR) is an effective tool for detecting shallow subsurface targets. In many GPR applications, these targets are veiled by the strong waves reflected from the ground surface, so that we need to apply a signal processing technique to separate the target signal from such strong signals. A pulse-compression technique is used in this research to compress the signal width so that it can be separated out from the strong contaminated clutter signals. This work introduces a filter algorithm to carry out pulse compression for GPR data, using a Wiener filtering technique. The filter is applied to synthetic and field GPR data acquired over a buried pipe. The discrimination method uses both the reflected signal from the target and the strong ground surface reflection as a reference signal for pulse compression. For a pulse-compression filter, reference signal selection is an important issue, because as the signal width is compressed the noise level will blow up, especially if the signal-to-noise ratio of the reference signal is low. Analysis of the results obtained from simulated and field GPR data indicates a significant improvement in the GPR image, good discrimination between the target reflection and the ground surface reflection, and better performance with reliable separation between them. However, at the same time the noise level slightly increases in field data, due to the wide bandwidth of the reference signal, which includes the higher-frequency components of noise. Using the ground-surface reflection as a reference signal we found that the pulse width could be compressed and the subsurface target reflection could be enhanced.

• Journal of the Korean Geophysical Society
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• v.6 no.3
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• pp.155-164
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• 2003

The validity and efficiency of the roll-along technique widely used in 2-D electrical resistivity survey are analyzed in case of the dipole-dipole and the Wenner-Schlumberger arrays by numerical modelling. The shallow anomalous resistivity bodies are successfully inverted both in the dipole-dipole and in the Wenner-Schlumberger arrays because the shallow data of pseudosection are not omitted by the roll-along technique. However, the deep anomalous resistivity bodies can not be well resolved due to the skip of observed data which is more significant in the Wenner-Schlumberger array having relatively poor horizontal coverage of obtaining data. Carrying out electrical survey adopting the dipole-dipole array, the skip of data is insignificant because it is unfeasible to expand the electrodes to the maximum electrode separation coefficient($n_max$) owing to low S/N ratio. In case of the Wenner-Schlumberger array, however, because it is generally feasible to expand the electrodes $n_max$ to the owing to high S/N ratio, it is highly possible that skip of data from the roll-along technique causes significant distortion of inversion results. Therefore, adopting the Wenner-Schlumberger array having deeper median depth(Edwards, 1977) than do the dipole-dipole array on condition of the same unit electrode spacing( ($a$) ) and $n_max$, it is recommended to determine $a$ based on not $n_max$but $n_prob$free from the skip of observing data and forward electrodes with keeping overlap interval 3/4 of the survey line length in order to reduce the distortion of resistivity structure and perform resistivity survey efficiently. These results are confirmed by numerical modelling.