• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.225-231
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• 2006

As a study of efficient velocity analysis in sonic log, several preexisting techniques have been adopted to the sonic data taken from model borehole in Kangwon National University, and the results were compared. For the data taken from monopole source, Slowness-Time Coherence method which is a common technique for nondispersive wave was used. For the data taken from dipole source, conventional STC and Tang's method(Tang et al., 1995) were used. From the good matches in the P and Stoneley wave velocities, we could confirm the effectiveness of STC computation. We also could find that shear velocity obtained from Tang's method were exactly matched with shear velocity obtained from monopole source, and that the velocity were within the range of S wave velocity values obtained from conventional STC application to dispersive flexural waves.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.26 no.1
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• pp.59-73
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• 1998

Sediment samples from five stations at the Shihwa Lake sewage outfall, west cost of Korea, were collected to evaluate the effect of the outfall on benthic foraminifers. Heavy metal (Cu and Zn) polluted the eastern part of the Shihwa Lake, adjacent to the Shihwa-Banwol Industrial Complexes, shows barren or nearly barren of benthic foraminifers, and the lowest number of species both at the core top and downcore. Excepting for the barren zone, pyritized benthic foraminifers abundantly occur both at the surface and downcore sediments in the western part of the Shihwa Lake, suggesting that foraminiferal disease by anoxic bacteria. Recent intrusion of pollutants form the Shihwa-Banwol Industrial Complexes and adjacent six major streams severely polluted the Shihwa Lake as shown by the low abundance (number/10 g) of benthic foraminifers, low number of Ammonia beccarii, low species diversity, and absence of both Elphidium spp. and ostracodes at the surface sediments compared of both downcore. Except the barren zone, both pyritized and non-pyritized Ammonia beccarii occur dominantly in the surface sediments and downcore. Elphidium spp. (either pyritized or non-phyritized) do not occur in the surface sediments of whole stations. However, they occur from the entire downcore sediments except in the eastern part of Shihwa Lake. Arenaceous foraminifers do not inhabit in the heavily polluted areas as evidenced by the occurrence of relatively deep core depth (11-15 cm). Ostracodes occur at the downcore sediments, but they do not occur at the surface sediments. Ostracodes also do not occur at the heavily polluted areas in the eastern part of the Shihwa Lake both at the surface and downcore sediments, indicating that the abundance of ostracodes also can be used for a pollution indicator.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.397-406
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• 2010

Resistivity method is a practical and effective geophysical technique to detect leakage zones in embankment dams. Generally, resistivity survey conducted along the crest assumes that the embankment dam has a 2D structure. However, the 3D topography of the embankment distorts significantly resistivity data measured on anywhere of the dam. This study evaluates the influence from 3D effects created by specific dam geometry and effects of water level fluctuations through the 3D finite element modeling technique. Also, a comparison between different locations of survey line are carried out, and topographic correction technique is developed for the resistivity data obtained along the embankment dam. Furthermore, using synthetic resistivity data for an embankment dam model with leakage zone, detectability of leakage zones is estimated through 2.5D inversion.

• Geophysics and Geophysical Exploration
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• v.21 no.4
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• pp.244-254
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• 2018

The first geophysical technique applied to the agricultural sector in Korea was electrical resistivity sounding and conducted in purpose of groundwater exploitation in the 1970s. According to the diversity of agricultural activities since the 1990s, various geophysical methods including electrical resistivity, electromagnetic induction, and self-potential method were applied to several agricultural fields such as soil characterization with saline concentration in vast reclaimed area, delineation of seawater intrusion regions in costal aquifer, safety inspection of embankment dikes with leakage problem, detection of ground subsidence from overpumping and tracing of groundwater aquifer contamination by leachate from livestock mortality burial or waste burial site. This paper introduces representative geophysical techniques that have been utilized in various agricultural fields and suggests several ways to develop the geophysical methods required for the precision agriculture field in the near future based on the past achievements.

• Proceedings of the KSRS Conference
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• v.2
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• pp.864-867
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• 2006

Thermal infrared images of Landsat-5 TM and Landsat-7 ETM+ sensors have been unrivalled sources of high resolution thermal remote sensing (60m for ETM+, 120m for TM) for more than two decades. Atmospheric effect that degrades the accuracy of Sea Surface Temperature (SST) measurement significantly, however, can not be corrected as the sensors have only one thermal channel. Recently, MODIS sensor onboard Terra satellite is equipped with dual-thermal channels (31 and 32) of which the difference of at-satellite brightness temperature can provide atmospheric correction with 1km resolution. In this study we corrected the atmospheric effect of Landsat SST by using MODIS data obtained almost simultaneously. As a case study, we produced the Landsat SST near the eastern and western coast of Korea. Then we have obtained Terra/MODIS image of the same area taken approximately 30 minutes later. Atmospheric correction term was calculated by the difference between the MODIS SST (Level 2) and the SST calculated from a single channel (31 of Level 1B). This term with 1km resolution was used for Landsat SST atmospheric correction. Comparison of in situ SST measurements and the corrected Landsat SSTs has shown a significant improvement in $R^2$ from 0.6229 to 0.7779. It is shown that the combination of the high resolution Landsat SST and the Terra/MODIS atmospheric correction can be a routine data production scheme for the thermal remote sensing of ocean.

• Geophysics and Geophysical Exploration
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• v.2 no.2
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• pp.112-121
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• 1999

This article reviews the development of geophysical inverse theory. In a series of articles published in 1967, 1968, and 1979, G. Backus and F. Gilbert a trade-off between model resolution and estimation errors in geophysical inverse problems, and gave a criterion to compromise the reciprocal relation. Although the criterion was not clear in the physical point of view, it had been extensively used in the interpretation of geophysical date in the 1970s. This was the starting point of the fruitful development of inverse theory in geophysics. A reasonable criterion to compromise the reciprocal relation was derived to solve linear problems by D. D. jackson in 1979, introducing the concept of a priori information about unknown model parameters. This Jackson's approach was extended to solve nonlinear problems on the basis o probabilistic approach to the inverse problems formulated by A. Tarantola and B. Vallete in 1982. At the end of 1980s ABIC (Akaike Bayesian Information Criterion) was introduced for selecting a more reasonable model in geophysics. Now the date inversion is regarded as the process of extracting new information from observed data, combining in with a priori information about model parameters, and constructing a more clear image of model.

• Journal of Astronomy and Space Sciences
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• v.20 no.1
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• pp.1-10
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• 2003

A precise kinematic orbit determination (P-KOD) procedure for Low Earth Orbiter(LEO) using the GPS ion-free triple differenced carrier phases is presented. Because the triple differenced observables provide only relative information, the first epoch's positions of the orbit should be held fixed. Then, both forward and backward filtering was executed to mitigate the effect of biases of the first epoch's position. p-KOD utilizes the precise GPS orbits and ground stations data from International GPS Service (IGS) so that the only unknown parameters to be solved are positions of the satellite at each epoch. Currently, the 3-D accuracy off-KOD applied to CHAMP (CHAllenging Min-isatellite Payload) shows better than 35 cm compared to the published rapid scientific orbit (RSO) solution from GFZ (GeoForschungsZentrum Potsdam). The data screening for cycle slips is a particularly challenging procedure for LEO, which moves very fast in the middle of the ionospheric layer. It was found that data screening using SNR (signal to noise ratio) generates best results based on the residual analysis using RSO. It is expected that much better accuracy are achievable with refined prescreening procedure and optimized geometry of the satellites and ground stations.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.633-636
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• 2007

The objective of this study is to measure backscattering coefficients of paddy rice using L, C, X-bands scatterometer system during a rice growth period. The measurement was conducted at an experimental field located in National Institute of Agricultural Science and Technology (NIAST), Suwon, Korea. The rice cultivar was a kind of Japonica type, called Chuchung. The scatterometer system consists of dual-polarimetric square horn antennas, HP8720D vector network analyzer (20MHz ${\sim}$ 20GHz), RF cables, and a personal computer that controls frequency, polarization and data storage. The scatterometer system is calibrated using a calibration kit (3.5mm, 85052D). The backscattering coefficients were calculated by applying radar equation for the measured at incidence angles between $20^{\circ}$ and $60^{\circ}$ for four polarization (HR, VV, HV, VH), respectively, and compared with rice growth data such as plant height, stem number, biomass, dry weight and LAI that were collected at time of each scatterometer measurement simultaneously.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.329-337
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• 2007

For seven NX sized borehole models constructed from physical property data for representative geology in Korea, dispersion curves were derived and compared between models having different physical parameters. By comparing and analyzing the dispersion curves obtained from different sources (monopole and dipole) and different borehole sizes (76 mm and 150 mm), dispersion characteristics in sonic log could be understood better, particularly in the case of slim hole sonic log.

• Geophysics and Geophysical Exploration
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• v.18 no.1
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• pp.14-20
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• 2015

Three-dimensional (3D) resistivity method is an effective tool in the engineering site survey because it can provide a 3D resistivity distribution of the site. In this study, we tried to find out faults, fractures and coal seams that can cause the collapse of the tunnel. We carried out 2D resistivity survey along 5 parallel lines and 11 cross lines and merged all the apparent resistivity data for 3D inversion. Finally, from the 3D resistivity image and drilling data we presented the 3D distribution of faults, fractures and coal seams that are considered the main cause of the tunnel collapse.