• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.330-335
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• 2010

In order to estimate the confidence level of the velocity distribution shown in a velocity image reconstructed from a travel-time tomography, the ray coverage and the inversion characteristics of the system matrix were investigated. The targets of the analysis is the first arrival travel-time, the raypath information, and the resulting velocity model. The ray coverage, degree of ray and model coupling, was estimated by the number of rays and total ray length in a velocity grid, and information regarding the resolution and uncertainties involved in the reconstructed velocity model was derived from the results of the SVD analysis of the system matrix that relates the data space (first arrival travel times) to the model space (velocity distribution in tomogram).

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.64-70
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• 1998

Diffraction tomography (DT) is a quantitative technique for high resolution subsurface imaging. In general DT algorithm is used for crosswell imaging. In this study high resolution GPR DT algorithm which is able to reconstruct high resolution image of subsurface structures in multi-monostatic geometry is developed. Developed algorithm is applied to finite difference data and its criteria of application and its limit are studied. Inversion parameters (number of imaging frequency, regularization factor, frequency range) are deduced from isolated weak scattering model. And the usuability of the algorithm is proved by applying to models which break the weak scattering approximation.

• Geophysics and Geophysical Exploration
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• v.11 no.4
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• pp.326-334
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• 2008

The resistivity method has been used to image the electrical properties of the subsurface. Especially, this method has become suitable for monitoring since data could be rapidly and automatically acquired. In this study, we developed a time-lapse inversion algorithm for the interpretation of resistivity monitoring data. The developed inversion algorithm imposes a big penalty on the model parameter with small change, while a minimal penalty on the model parameter with large change compared to the reference model. Through the numerical experiments, we can ensure that the time-lapse inversion result shows more accurate and focused image where model parameters have changed. Also, applying the timelapse inversion method to the leakage detection of an embankment dam, we can confirm that there are three major leakage zones, but they have not changed over time.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.177-183
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• 2008

The sub-salt imaging technique becomes more crucial to detect the hydro-carbonates in petroleum exploration as the target reservoirs get deeper. However, the weak reflections from the sub-salt structures prevent us from obtaining high fidelity sub-salt image. As an effort to overcome this difficulty, we applied the waveform inversion by implementing multi-grid technique to the sub-salt imaging. Through the comparison between the conventional waveform inversion using fixed grid and the multi-grid technique, we confirmed that the waveform inversion using multi-grid technique has advantages over the conventional fixed grid waveform inversion. We showed that the multi-grid technique can complement he velocity estimation result of the waveform inversion for imaging the sub-salt structures, of which velocity model cannot be obtained correctly by the conventional fixed grid waveform inversion.

• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.7-12
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• 2003

The lineament extraction from satellite images is important in the geologic studies including groundwater and mineral exploration, groundwater survey, natural hazard analysis, and many others. The lineaments in remote sensing images are identified by the difference of pixel values or brightness. Since the visual interpretation is apt to be influenced by the knowledges and experiences, many of the automatic lineament detection algorithms are developed to ensure the objectives and efficient outputs. DSTA (dynamic segment tracing algorithm) is one of such algorithms, which can be applied to not only mountainous area but also alluvial area. However, when the alluvial area is wider than mountain region, somewhat severe noises are generated. To reduce such noises, AERA (alluvial effect reducing algorithm) is proposed and tested for the image which contains mountains, cultivated land and urban area. Upon the application of AERA, alluvial effects in lineament extraction from satellite image are substantially reduced.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.185-192
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• 2002

We made a study of 3-D migration which could precisely image data of GPR (Ground Penetrating Radar) applied to NDT (Non-Destructive Test) field for the inspection of structural safety. In this study, we obtained 3-D migrated images of important targets in structuresurvey (e.g. steel pipes, cracks) by using 3-D Kirchhoff prestack depth migration scheme developed for seismic data processing. For a concrete model consisting of steel pipe and void, the targets have been well defined with opposite amplitude according to the parameters of the targets. And migrated images using Parallel-Broadside array (XX configuration) have shown higher resolution than those using Perpendicular-Broadside array (YY configuration) when steel pipes had different sizes. Therefore, it is required to analyze the migrated image of XX configuration as well as that of general YY configuration in order to get more accurate information. As the last stage, we chose a model including two steel pipes which cross each other. The upper pipe has been resolved clearly but the lower has been imaged bigger than the model size due to the high conductivity of the upper steel.

• Proceedings of the KSRS Conference
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• 1998.09a
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• pp.95-100
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• 1998

The purpose of this study is to describe the change of the spring bloom and oceanographic condition. The variation of pigment concentration derived from the satellite ocean color data has been analyzed. According to the movement of blooming area, blooming was very concerned with a rising trend of sea surface temperature and a supply of nutrients. A nutrient rich water carried by the Oyashio encounters with the warm Core ring, where mixings and blooms are observed. We examined the correlation by using the satellite observations of the temperature and chlorophyll-a for the spring seasons (May, June, July) of 1998 the off Sanriku area (38-43N, 141- l50E). Using the SeaWiFS data, we process the data into the level-3, which contains the geophysical value of chlorophyll-a. And chlorophyll-a data is mapped for the water between 110E and 160E, and 15N and 52N with a 0.08 * 0.05 degree grid for each image. And Sea Surface Temperature (SST) data is produced using the AVHRR onboard the NOAA. The SST is derived by the MCSST. Then, the data is mapped for the water as much as chi-a data. And these gridded image was made by detection of each water masses, which are Kuroshio Extension, the warm-core ring and the Oyashlo Intrusion, etc., using those satellite images to determine short term change. Off Sanriku is a place where warm-water pool and the Oyashio at-e mixed. When warm streamer has intruded in cold water, the volume of phytoplankton increases at the tip of warm streamer. Warm water streamer was trigger of occurring blooming. And also, SeaWiFS images provided as much information for the studies of chlorophyll-a concentrations in the surface.

• Geophysics and Geophysical Exploration
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• v.5 no.1
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• pp.33-45
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• 2002

It was necessary to devise new techniques to overcome and enhance the resolution limits of traveltime tomography. Waveform inversion has been one of the methods for giving very high resolution result. High resolution image could be acquired because waveform inversion used not only phase but amplitude. But waveform inversion was much time consuming Job because forward and backward modeling was needed at each iteration step. Velocity-stress method was used for effective modeling. Resolution limits of imaging methods such as travel time inversion, acoustic and elastic waveform inversion were investigated with numerical models. it was investigated that Resolution limit of waveform inversion was similar tn resolution limit of migration derived by Schuster. Horizontal resolution limit could be improved with increased coverage by adding VSP data in cross hole that had insufficient coverage. Also, waveform inversion was applied to realistic models to evaluate applicability and using initial guess of travel time tomograms to reduce non-linearity of waveform inversion showed that the better reconstructed image could be acquired.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.191-201
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• 1999

The interpretation of resistivity data has, so far, mainly been made under the assumption that the earth is of relatively simple structure and then using one or two-dimensional inversion scheme. Since real earth structure and topography are fully three-dimensional and very complicated In nature, however, such assumptions often lead to misinterpretation of the earth structures. In such situations, three-dimensional inversion is probably the only way to get correct image of the earth. In this study, we have developed a three-dimensional inversion code using the finite element solution for the forward problem. The forward modeling algorithm simulates the real field situation with irregular topography. The inverse problem is solved iteratively using the least-squares method with smoothness constraint. Our inversion scheme employs ACB (Active Constraint Balancing) to enhance the resolving power of the inversion. Including Irregular surface topography in the inversion, we can accurately define the earth structures without artifact in the numerical tests. We could get reasonable image of earth structure by Inverting the real field data sets taken over highway bridge construction site.

• Journal of English Language & Literature
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• v.57 no.2
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• pp.237-264
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• 2011

Based on its geophysical feature, the island has long been recognized as a separate and self-sustaining space independent of neighboring continent or other islands. Literary tradition has used the island as a metaphor for a utopian alternative to mundane human society with its various kinds of wrongdoings. Recent nature writings have taken up this island metaphor to emphasize the wholeness of the ecosystem in specifically designated natural community or landscapes such as national parks or wilderness preservation areas. Human-nature relations as border-divided area is also recognized as the island. Modern island biogeography, however, has disproved such a concept of islands as autonomous, revealing the contrasting fact that the richness of species on an undisturbed island is determined largely by species immigration from and emigration to a source of colonists. This scientific finding has posited the island as the interconnected nature, but the public and metaphoric use of it still resorts to the old concept of it as isolated and autonomous nature, because this image has been ingrained deeply in our consciousness and culture. Considering the negative consequences from the recognition of nature and nature-humans as isolated space, we need a new nature metaphor that embodies interconnectedness in nature and of human-nature relations. Such feature of interconnectedness is best embedded in the concept of ecotone. Some ecotones are created and maintained through human participation in nature, and this human induced nature of ecotone denotes the possibilities of a constructive relation between them. The substitution of the island with the ecotone as the concept of nature and the image of human-nature relations is expected to correct ecocritical practices of reading of nature writing, which has been predominantly interpreted within the orientation of nature itself and nature-human relations as an isolated and self-autonomous island. Adopting the ecotone in literary study enables ecocriticism to dig out cultural elements embedded in nature writing and reveal socio-political, ideological factors hidden behind the writers' portrayal of nature as islands.