• Geophysics and Geophysical Exploration
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• v.14 no.3
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• pp.185-190
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• 2011

In marine controlled-source electromagnetic (CSEM) modeling, it may be difficult to evaluate primary fields accurately using conventional linear filters because they decay very rapidly with distance. However, since there exists a closed-form solution to the Hankel transform in TM mode for a homogeneous half space, we can assess the accuracy of linear filters for evaluating the Hankel transform. As a result, only nine out of 36 source-receiver pairs show that EM fields decrease linearly in semi-log scale with an increase of source-receiver distance, while EM fields are either 0 or not reduced significantly due to an effect of the air layer. There also exist closed-form solutions for the nine pairs, and the others can be evaluated accurately with a relatively short filter. This paper proposes a method which uses closed-form solutions for TM-mode Hankel transforms and a filter with 61 coefficients for TE-mode ones.

• Geophysics and Geophysical Exploration
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• v.14 no.3
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• pp.254-260
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• 2011

We studied magnitude determination method using high-frequency energy radiation duration to calculate rapidly magnitude of large earthquakes that occurred around Japan. Fourteen earthquakes were analyzed using Korea Meteorological Administration (KMA) data. We calculated duration of high-frequency energy radiation with 2~4 Hz band pass filter at each data and estimated magnitude. As a result, duration becomes longer as magnitude becomes larger and the magnitude estimated using regional earthquake data are similar to that using teleseismic data. Therefore when an earthquake occurs around Japan we will be able to estimate the magnitude in a relatively short time using KMA data and it may be possible to determine if the earthquake is large enough to produce tsunami.

• Geophysics and Geophysical Exploration
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• v.17 no.2
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• pp.88-94
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• 2014

Due to mechanical failure or geographical accessibility, the seismic data can be partially missed. In addition, it can be coarsely sampled such as crossline of the marine streamer data. This seismic data that irregular sampled and spatial aliased may cause problems during seismic data processing. Accurate and efficient interpolation method can solve this problem. Futhermore, interpolation can save the acquisition cost and time by reducing the number of shots and receivers. Among various interpolation methods, the Matching Pursuit method can be applied to any sampling type which is regular or irregular. However, in case of using sinusoidal basis function, this method has a limitation in spatial aliasing. Therefore, in this study, we have developed wavelet based Matching Pursuit method that uses wavelet instead of sinusoidal function for the improvement of dealiasing performance. In addition, we have improved interpolation speed by using inner product instead of L-2 norm.

• Geophysics and Geophysical Exploration
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• v.17 no.2
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• pp.95-103
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• 2014

This paper presents a practical inversion method for recovering a three-dimensional (3D) resistivity model and static shifts simultaneously. Although this method is based on a Gauss-Newton approach that requires a sensitivity matrix, the computer time can be greatly reduced by implementing a simple and effective procedure for updating the sensitivity matrix using the Broyden's algorithm. In this research, we examine the approximate inversion procedure and the weighting factor ${\beta}$ for static shifts through inversion experiments using synthetic MT data. In methods using the full sensitivity matrix constructed only once in the iteration process, a procedure using the full sensitivity in the earlier stage is useful to produce the smallest rms data misfit. The choice of ${\beta}$ is not critical below some threshold value. Synthetic examples demonstrate that the method proposed in this paper is effective in reconstructing a 3D resistivity structure from static-shifted MT data.

• Korean Journal of Remote Sensing
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• v.28 no.2
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• pp.237-243
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• 2012

In this paper, an atmospheric effect of repetitive measurements of X-band (9.65 GHz) arc-rail type GB-SAR (ArcSAR) system was quantitatively analyzed. Four artificial triangular trihedral corner reflectors as stationary targets for getting stable back scattered signal during 43 hours continually. The results of the analysis showed that the phase of those stationary targets had changed maximum of 5 radian (12.4 mm) and total RMS error had was 1.62 radian (4 mm) during 65 repeated measuring time. The refractive index of air which was calculated using the temperature;humidity and pressure of atmosphere showed very close relationship with the phase difference. We could check the atmospheric correction was fulfilled by the correction of an atmospheric effect using refractive index during the selected 16 hours period showed that RMS error was dropped from 1.74 radian (4.3 mm) to 0.10 radian (0.24 mm).

• Journal of the Korean earth science society
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• v.30 no.2
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• pp.165-175
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• 2009

The East Sea including the area of this study is identified as a typical back-arc sea located in the backside of the Circum-Pacific volcanic and earthquake belt. Previous studies reported that the East Sea has begun to open by tensile force and formed its current shape. In this study, we investigate the regional tectonic structure of the East Sea using ship-borne gravity, magnetic, and satellite gravity data. The result of three-dimensional depth inversion shows that Moho depth of the study area is approximately 13-25km and inversely proportional to the thickness of the crust. In addition, as approaching to the center of the Ulleung Basin (UB), the thickness of the crust of the UB becomes thinner due to the extension caused by tensile force which had opened the East Sea.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.615-620
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• 2002

Probability distribution of the sea surface slope is estimated using sun glitter images derived from visible radiometer on Geostationary Meteorological Satellite (GMS) and surface vector winds observed by spaceborne scatterometers. The brightness of the visible images is converted to the probability of wave surfaces which reflect the sunlight toward GMS in grids of 0.25 deg $\times$ 0.25 deg. Slope and azimuth angle required for the reflection of the sun's ray toward GMS are calculated for each grid from the geometry of GMS observation and location of the sun. The GMS images are then collocated with surface wind data observed by three scatterometers. Using the collocated data set of about 30 million points obtained in a period of 4 years from 1995 to 1999, probability distribution function of the surface slope is estimated as a function of wind speed and azimuth angle relative to the wind direction. Results are compared with those of Cox and Munk (1954a, b). Surface slope estimated by the present method shows narrower distribution and much less directivity relative to the wind direction than that reported by Cox and Munk. It is expected that their data were obtained under conditions of growing wind waves. In general, wind waves are not always developing, and slope distribution might differ from the results of Cox and Munk. Most of our data are obtained in the subtropical seas under clear-sky conditions. This difference of the conditions may be the reason for the difference of slope distribution.

• Journal of Soil and Groundwater Environment
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• v.17 no.5
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• pp.10-19
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• 2012

The aim of this study was to examine chemical and isotopic compositions of groundwater and lake water near an area contaminated by petroleum and to evaluate influence of petroleum on them during the period from March to August 2011. In dry season, $Ca^{2+}$ and $SO{_4}^{2-}$ were dominant in the groundwater and lake water and $Ca^{2+}$ and $HCO{_3}^-$ were significant in wet season. ${\delta}^{18}O$ and ${\delta}D$ of the groundwater and lake water were plotted near LMWL (${\delta}D=8.06{\delta}^{18}O+12.5$). ${\delta}^{18}O$ and ${\delta}D$ of the lake water did not show seasonal variation. However, ${\delta}^{18}O$ and ${\delta}D$ of the groundwater were enriched in wet season compared with those in dry season because of influence of small ponds around wells where evaporation losses were slightly experienced. Redox condition of most lake water was oxidation environment in contact with the atmosphere during the study period. However, redox condition of groundwater was transitional environment in dry season and oxidation environment in wet season because of influence of contaminant such as petroleum. In some groundwater, the concentrations of $NO{_3}^-$ in some groundwater were less than 1 mg/L because of denitrification. Also, $NO{_3}^-$ showed positive correlation with $SO{_4}^{2-}$ and weak negative correlation with $HCO{_3}^-$, because of influence of denitrification.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.5
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• pp.523-530
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• 2010

Recently more gravity data is being obtained due to the increased demands from the fields of geodesy, geophysics, and military. In general, the observed gravity values are corrected for the effect of tide, instrument drift, and instrument height to generate the absolute gravity values at a point. Until yet, the models for tide and drift corrections and those procedures are not determined in Korea which led to the inconsistent data processing for different data sets. Therefore, in this study, the models for tide and drift are analyzed to select the appropriate models. Based on the analysis, it was found that there is not much difference between Longman and Tamura tide models for celestial objects. Earth tide, however, should be considered in tide correction procedure. In drift corrections, the difference between the model considering only the common points and that considering all points appears significantly large up to 0.04mGal. In this case, the model with all points should be used as it the correct one according to the adjustment theory and it generates estimates with better precision.

• Economic and Environmental Geology
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• v.38 no.4 s.173
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• pp.381-394
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• 2005

Mokpo city is a coastal city located at the south western coast of the Korean Peninsula. Large regions within Mokpo are subjected to significant subsidence because about $70\%$ of the city area is a reclaimed land from the sea. Although no confidential quantitative measurements are available up to the present, the subsidence rate is as much as several cm per year. In this study, we aimed to estimate the subsidence rate over Mokpo city by using twenty-six JERS-1 SAR dataset from September 1992 to October 1998. Several tens of differential interferograms were processed from JERS-1 dataset and STRM 3-arc DEM. The results indicate continuous subsidence in Dongmyung-dong, Hadang-dong and Wonsan-dong in city, and the subsidence velocity reach over 4 cm/yr in the most highly sinking area. For facilitating the analysis of time-varying surface change, we also carried out an interferometric SAR time series analysis using permanent scatterer and consequently determined space-time maps of surface deformation at each acquisition time of JERS- 1 SAR.