• Geophysics and Geophysical Exploration
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• v.19 no.2
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• pp.76-83
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• 2016

Migration image can be distorted due to reflected waves in the source and receiver wavefields when discontinuities of input velocity model exist in seismic imaging. To remove reflected waves coming from layer interfaces, it is a common practice to smooth the velocity model for migration. If the velocity model is smoothed, however, the subsurface image can be distorted because the velocity changes around interfaces. In this paper, we attempt to minimize the distortion by reducing reflection energy in the source and receiver wavefields through acoustic impedance homogenization. To make acoustic impedance constant, we define fake density model and use it for migration. When the acoustic impedance is constant over all layers, the reflection coefficient at normal incidence becomes zero and the minimized reflection energy results in the improvement of migration result. To verify our algorithm, we implement the reverse-time migration using cell-based finite-difference method. Through numerical examples, we can note that the migration image is improved at the layer interfaces with high velocity contrast, and it shows the marked improvement particularly in the shallow part.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.1-15
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• 2020

The Mohr-Coulomb model is mainly used in evaluating the behavior of the ground in numerical analyses of domestic ground excavation. This study analyzes its limitations and compares its numerical results with the hyperbolic model, a model that closely follows actual ground behavior during excavation. Recent applications of the Mohr-Coulomb model in Korea have tended to impose arbitrary special boundary conditions to control the problem of excessive heaving of the ground excavation surface. This adjustment only controls the size of the heaving of the excavation surface, implying that the ground behavior is distorted from the actual behavior. This study compares results from the hyperbolic model (hardening soil model) and the Mohr-Coulomb model, and confirms that the hyperbolic model provides both a more-suitable solution to the problem of heaving during excavation and the actual stress-strain behavior. In numerical analyses of ground excavation, the hyperbolic model is expected to give results consistent with the actual ground behavior.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.113-119
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• 2019

This study aims at the analysis using the Resistivity Estimation Model (REM) to examine the effect of specimen size on the measurement of electrical resistivity. In the experiment, specimens of concrete were fabricated and the apparent resistivity was measured for each electrode interval. The apparent resistivity measured was found to be distorted in the apparent resistivity as the specimen size became smaller and closer to the outside (edge). As a result of comparing the experimental and analysis values, it is expected that REM can be used to examine the effect of the size of the specimen.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.4
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• pp.391-399
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• 2012

Multipath remains a dominant source of ranging errors in GNSS (Global Navigation Satellite System). And it is generally considered undesirable in the context of GNSS, since the reception of multipath can make significant distortion to the shape of the correlation function. In this paper, therefore, the model of the distorted shape of the correlation function is formulated and a MBME (Model-Based Multipath Estimation) technique for GPS L1/L5 receivers is proposed in order to estimate the parameters of the indirect signal such as the amplitude and the delay. The MBME technique does not require the any hardware modifications and it can estimate the parameters for both the short and long-delay multipath. Especially, it would be the very effective technique for the short-delay multipath if the L5 signal is available. Finally, the feasibility of the proposed technique has been confirmed by simulation results.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.815-823
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• 2006

The hydrologic cycle in urban catchment has been changed due to the expansion of impervious area by rapid urban development. In this study, the SWMM 5 (Storm Water Management Model 5) model was used to simulate the hydrologic cycle of the Dorimcheon catchment which suffers from the distorted hydrologic cycle as a typical urban catchment. This study compare continuous simulation of urban runoff combining the channel and sewer system with that of channel only in the Dorimcheon catchment. Continuous simulations of urban runoff were performed for the upstream basin of Dorim bridge. The urban impervious regions were processed by the land use analysis from LANDSAT_TM images. It was performed from 1975 to 2000 for every five years. Surface, groundwater and wastewater runoffs were additionally included in the simulations one at a time. Such simulations made it possible to evaluate those components quantitatively. The result of continuous simulation of urban runoff combining the channel and sewer system is that peak flow and recession are well simulated. The analysis results of urbanization effect on runoff are as follows: the surface runoff in 2000 increases to 64% of the whole precipitation whereas the surface runoff in 1975 amounts to 46% of the precipitation; the groundwater runoff in 2000 amounts to 6% and shows 8% decrease during the period from 1975 to 2000.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.58 no.4
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• pp.352-358
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• 2022

We explored the frequency response of krill target strength (TS) to understand the Antarctic krill (Euphausia superba) and ice krill (Euphausia crystallorophias) using the stochastic distorted-wave Born approximation (SDWBA) model. The results showed that the distribution of orientation and the fatness factor could significantly impact on the frequency response of TS. Krill TS is clearly depended on acoustic properties, which could affect to estimate the biomass of two krill species. The results provide insight into the importance of understanding TS variation to estimate the Antarctic krill and ice krill biomass, and their ecology related to the environmental features in the Southern Ocean.

• Journal of KIISE
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• v.42 no.11
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• pp.1372-1379
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• 2015

This paper presents an analysis of feature extraction methods used for distinguishing the speech of patients with cleft palates and people with normal palates. This research is a basic study on the development of a software system for automatic recognition and restoration of speech disorders, in pursuit of improving the welfare of speech disabled persons. Monosyllable voice data for experiments were collected for three groups: normal speech, cleft palate speech, and simulated clef palate speech. The data consists of 14 basic Korean consonants, 5 complex consonants, and 7 vowels. Feature extractions are performed using three well-known methods: LPC, MFCC, and PLP. The pattern recognition process is executed using the acoustic model GMM. From our experiments, we concluded that the MFCC method is generally the most effective way to identify speech distortions. These results may contribute to the automatic detection and correction of the distorted speech of cleft palate patients, along with the development of an identification tool for levels of speech distortion.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.4 s.304
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• pp.59-68
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• 2005

This paper proposes a face recognition under varying poses using local area obtained by side-view pose normalization. General normalization methods for face recognition under varying pose have a problem with the information about invisible area of face. Generally this problem is solved by compensation, but there are many cases where the image is distorted or features lost due to compensation .To solve this problem we normalize the face pose in side-view to reduce distortion that happens mainly in areas that have large depth variation. We only use undistorted area, removing the area that has been distorted by normalization. We consider two cases of yaw pose variation and pitch pose variation, and by experiments, we confirm the improvement of recognition performance.

• Journal of Power Electronics
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• v.18 no.1
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• pp.171-184
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• 2018

Unbalanced and distorted grid voltages cause the grid side current of a current source PWM rectifier to be heavily distorted. They can also cause the DC-link current to fluctuate with a huge amplitude. In order to enhance the performance of a current-source PWM rectifier under unbalanced and harmonic grid voltage conditions, a mathematical model of a current-source PWM rectifier is established and a flexible multi-objective control strategy is proposed to control the DC-link current and grid-current. The fundamental positive/negative sequence, $5^{th}$ and $7^{th}$ order harmonic components of the grid voltage are first separated with the proposed control strategy. The grid current reference are optimized based on three objectives: 1) sinusoidal and symmetrical grid current, 2) sinusoidal grid current and elimination of the DC-current $2^{nd}$ order fluctuations, and 3) elimination of the DC-current $2^{nd}$ and $6^{th}$ order fluctuations. To avoid separation of the grid current components, a multi-frequency proportional-resonant controller is applied to control the fundamental positive/negative sequence, $5^{th}$ and $7^{th}$ order harmonic current. Finally, experimental results verify the effectiveness of proposed control strategy.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.12
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• pp.1923-1932
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• 2013

In order to solve the problem of severely distorted images from a wide-angle camera, we propose a calibration method which corrects a radial distortion in wide-angle images by estimation and validation of camera model. First, we estimate a camera model consisting of intrinsic and extrinsic parameters from calibration patterns, where intrinsic parameters are the focal length, the principal point and so on, and extrinsic parameters are the relative position and orientation of calibration pattern from a camera. Next we validate the estimated camera model by re-extracting corner points by inversing the model to images. Finally we correct the distortion of the image using the validated camera model. We confirm that the proposed method can correct the distortion more than 80% by the calibration experiments using the lattice shaped pattern images captured from a general web camera and a wide-angle camera.