• 한국지능시스템학회논문지
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• 제25권1호
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• pp.29-34
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• 2015

Brain-computer interface 기술은 일상에서 편안한 생활을 위해 다방면으로 연구가 진행 중이다. 본 연구는 3가지 동작의 뇌파특성을 분석하여 의수와 같은 외부기기의 세밀한 동작 제어를 목적으로 한다. 피험자들은 악력기를 쥘 때 (Grip), 손가락만을 움직일 때 (Move), 아무런 동작을 취하지 않을 때 (Relax)의 3가지 동작을 수행하였고, 뇌파를 측정하여 power spectrum analysis와 multi-common spatial pattern 알고리즘으로 특징추출을 수행하였으며, 분류알고리즘인 SVM(support vector machine)으로 뇌파의 특징데이터들을 분류하였다. 실험결과 3개의 다른 동작을 분류한 결과, 실험에 참여한 3명의 피험자 중 2명에게서 Grip 클래스의 분류율이 가장 높은 분류율을 보였다. 본 연구의 결과는 뇌파를 이용하여 의수가 필요한 환자들에게 유용할 것으로 기대한다.

• 대한원격탐사학회지
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• 제39권6_1호
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• pp.1517-1522
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• 2023

본 연구에서는 Second Simulation of the Satellite Signal in the Solar Spectrum Vector를 활용하여 Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD)의 기대 오차(expected error, EE)가 KOMPSAT-3A 지표반사도(surface reflectance, SR)의 정확도에 미치는 영향을 평가한다. 연구에서 다양한 지상 AOD와 그에 따른 MODIS AOD EE를 고려함으로써, 파장이 짧고 태양천정각(solar zenith angle, SZA)이 높을수록 SR 오류가 증가한다는 결과를 확인했으며, 이는 파장과 SZA 고려 사항을 통합하여 대기보정 알고리즘을 개선하기 위한 추가 연구가 필요하다는 점을 강조한다. 또한, 이 연구는 대기보정 과정에서 다른 위성의 AOD 자료 활용에 대해 더 잘 이해하기 위한 기초 자료를 제공하고 대기보정 기술 발전에 기여할 것으로 예상한다.

• 지구물리와물리탐사
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• 제10권4호
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• pp.241-251
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• 2007

본격적인 지진관측 이래 최대 규모의 내륙 지진으로 기록된 오대산지진의 관측 스펙트럼을 이용하여, 점지진원 스펙트럼 모델의 지진원 크기 및 오차의 공간적인 특성을 평가하였다. 먼저 지진원 스펙트럼을 추정하기 위해, 최근까지 국내에 축적된 지진자료를 기반으로 비교적 상세하게 추정된 추계학적 지진동모델(Boore, 2003)의 지진파 전달, 부지특성(연관희, 2007)을 이용하여 관측 자료를 보정하였다. 추정된 오대산지진의 지진원 스펙트럼을 $1-f_c$(1개의 코너주파수) Brune의 ${\omega}^2$ 지진원모델에 적합한 결과, 기존에 제시된 지진규모-응력강하량 대표모델(연관희 등, 2006)에 의해 잘 예측되었으며, 오대산지진의 지진원 스펙트럼은 최근까지 한반도 인근에서 발생한 중규모 이상의 지진원 스펙트럼으로부터 추정된 $2-f_c$(2개의 코너주파수)의 경험적인 지진원모델에 보다 잘 부합되었다. 또한 일반적으로 무작위 잡음으로 취급되는 점지진원 지진파 스펙트럼 모델링 오차에 대해 방위각에 따른 방향성과 지역별 전달특성을 평가한 결과, 오차가 완전한 무작위 특성이 아님을 확인할 수 있었다. 이러한 모델링 오차의 방향성은 이론적으로 추정된 방사패턴과도 매우 유사한 관측된 방사패턴을 나타내었으며, 지역별로는 지질학적인 경계 혹은 지진파전달의 불연속적 특성과 밀접한 관계가 있는 것으로 판단되는 주파수별로 상이한 공간적인 분포 특성을 보여주었다.

• 대한원격탐사학회지
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• 제33권4호
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• pp.351-358
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• 2017

A new method to decompose the footprints of marine atmosphere boundary layer (MABL) on Synthetic Aperture Radar (SAR) imagery into characteristic spatial scales is proposed. Using two-dimensional Empirical Mode Decomposition (EMD) we obtain three Intrinsic Mode Functions (IMFs), which mainly present longitudinal rolls, three-dimensional cells and atmospheric gravity waves (AGW). The rolls and cells have spatial scales between 3.0 km and 3.8 km and between 5.3 km and 7.1 km, respectively. Based on previous observations and mixed-layer similarity theory, we estimated MABL's depths that vary from 0.95 km to 1.2 km over the rolls and from 3.0 km to 3.8 km over the cells. The AGW has maximum spectrum at 14.3 km wavelength. The method developed in this work can be used to decompose other satellite imageries into individual features through characteristic spatial scales.

• Advances in Computational Design
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• 제8권3호
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• pp.219-236
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• 2023

In this paper, finite element modeling of the laser ultrasonics (LU) process in ablation regime is of interest. The momentum resulting from the removal of material from the specimen surface by the laser beam radiation in ablation regime is modeled as a pressure pulse. To model this pressure pulse, two equations are required: one for the spatial distribution and one for the temporal distribution of the pulse. Previous researchers have proposed various equations for the spatial and temporal distributions of the pressure pulse in different laser applications. All available equations are examined and the best combination of the temporal and spatial distributions of the pressure pulse that provides the most accurate results is identified. This combination of temporal and spatial distributions has never been used for modeling laser ultrasonics before. Then by using this new model, the effects of variations in pulse duration and laser spot radius on the shape, amplitude, and frequency spectrum of ultrasonic waves are studied. Furthermore, the LU in thermoelastic regime is simulated by this model and compared with LU in ablation regime. The interaction of ultrasonic waves with a defect is also investigated in the LU process in ablation regime. Good agreement of the results obtained from the new finite element model and available experimental data confirms the accuracy of the proposed model.

• 정보보호학회논문지
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• 제9권3호
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• pp.39-52
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• 1999

본 논문에서는 저작권 보호를 위한 워터마크 내장 방법으로 공간 스케일 변수를 사 용한 공간 마 스킹 방법을 제안한다. 일반적으로 워터마크 알고리즘에서영상에 삽입되는 워터마크의 크 기가 클수록 삽입된 워터마크는 여러 가지 변형에 강인하게 되지만 워터마크된 영상의 화질을 보장하기 어렵다. 반 대로 워터마크의 크기가 작게 되면 양질의 영상을 얻을수 있으나 삽입된 워터 마크의 강인 성을 보장할 수 없는 서로 상반되는 특성을 가지고 있다. 따라서 워터마크의 강인성과 영상의 화질 사이 의 타협점을 구하는 것은 매우 어렵다, 본 논문에서는 이와 같은 문제를 해결하기 위해 공간 마스킹을 사용하였다. 즉 대역 확산 기법으로 워터마크된 영상에 공간 마스킹을 하므로써 텍스쳐 영역과 같은 워 터마크가 인 간시각에 민감하지 않지만 압축 손실이 일어나는 복잡한 영역에서는 압축손실과 같은 일반 적인 영상 처 리에 강하도록 공간 마스킹으로 워터마크의 크기를 크게 하였으며 워터마크를 삽입하기 어 려운 즉 노이 즈에 민감하지만 압축 손실과 일반적인 영상 처리에 강한 평탄 영역에서는 워터 마크 삽입 으로 인한 화 질저하를 방지하기 위해 공간 마스킹으로 워터 마크의 크기를 작게 해 워터마크 삽입으로 인한 화질저 하를 방지하였다. 따라서 본 논문에서 제안한 워터마킹 기법은 워터마크된 영상이 공간 마 스킹에 의해 워터마크의 크기를 조절할 수 있어 영상의 질과 워터마크의 강인성 모두를 만족할수 있 다. 그리고 본 논문에서 제안한 워터마킹 방법이 손실 압축(JPEG)과 잡음 그리고 축소 및 확대 클리핑 (Clipping) 컬류 션(Collusion)등과 같은 신호처리에 강인함을 실험을 통해 입증하였다. In this paper we propose a new watermarking technique for copyright protection of images. The proposed technique is based on a spatial masking method with a spatial scale parameter. In general it becomes more robust against various attacks but with some degradations on the image quality as the amplitude of the watermark increases. On the other hand it becomes perceptually more invisible but more vulnerable to various attacks as the amplitude of the watermark decreases. Thus it is quite complex to decide the compromise between the robustness of watermark and its visibility. We note that watermarking using the spread spectrum is not robust enought. That is there may be some areas in the image that are tolerable to strong watermark signals. However large smooth areas may not be strong enough. Thus in order to enhance the invisibility of watermarked image for those areas the spatial masking characteristics of the HVS(Human Visual System) should be exploited. That is for texture regions the magnitude of the watermark can be large whereas for those smooth regions the magnitude of the watermark can be small. As a result the proposed watermarking algorithm is intend to satisfy both the robustness of watermark and the quality of the image. The experimental results show that the proposed algorithm is robust to image deformations(such as compression adding noise image scaling clipping and collusion attack).

• Wind and Structures
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• 제17권1호
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• pp.43-68
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• 2013

The fluctuating wind induced vibration is one of the most important factors which has been taken into account in the design of long-span bridge due to the low stiffness and low natural frequency. Field measurement characteristics of sustained wind on structure site can provide accurate wind load parameters for wind field simulation and structural wind resistance design. As a suspension bridge with 1490 m main span, the Runyang Suspension Bridge (RSB) has high sensitivity to fluctuating wind. The simultaneous and continuously wind environment field measurement both in mid-span and on tower top is executed from 2005 up to now by the structural health monitoring system installed on this bridge. Based on the recorded data, the wind characteristic parameters, including mean wind speed, wind direction, the turbulence intensity, the gust factors, the turbulence integral length, power spectrum and spatial correlation, are analyzed in detail and the coherence functions of those parameters are evaluated using statistical method in this paper. The results indicate that, the turbulence component of sustain wind is larger than extremely strong winds although its mean wind speed is smaller; the correlation between turbulence parameters is obvious; the power spectrum is special and not accord with the Simiu spectrum and von Karman spectrum. Results obtained in this study can be used to evaluate the long term reliability of the Runyang Suspension Bridge and provide reference values for wind resistant design of other structures in this region.

• ETRI Journal
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• 제43권5호
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• pp.869-880
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• 2021

Herein, we estimate the direction of arrival (DOA) of non-Gaussian signals for nested arrays (NAs) by implementing the fourth-order difference co-array (FODC) and successive methods. In particular, considering the property of the fourth-order cumulant (FOC), we first construct the FODC of the NA, which can obtain O(N⁴) virtual elements using N physical sensors, whereas conventional FOC methods can only obtain O(N²) virtual elements. In addition, the closed-form expression of FODC is presented to verify the enhanced degrees of freedom (DOFs). Subsequently, we exploit the vectorized FOC (VFOC) matrix to match the FODC of the NA. Notably, the VFOC matrix is a single snapshot vector, and the initial DOA estimates can be obtained via the discrete Fourier transform method under the underdetermined correlation matrix condition, which utilizes the complete DOFs of the FODC. Finally, fine estimates are obtained through the spatial smoothing-Capon method with partial spectrum searching. Numerical simulation verifies the effectiveness and superiority of the proposed method.

• 대한원격탐사학회지
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• 제37권1호
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• pp.161-167
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• 2021

This paper presents the method to quantitatively evaluate the uncertainty of the semi-empirical Bidirectional Reflectance Distribution Function (BRDF) model for Himawari-8/AHI. The uncertainty of BRDF modeling was affected by various issues such as assumption of model and number of observations, thus, it is difficult that evaluating the performance of BRDF modeling using simple uncertainty equations. Therefore, in this paper, Monte-Carlo method, which is most dependable method to analyze dynamic complex systems through iterative simulation, was used. The 1,000 input datasets for analyzing the uncertainty of BRDF modeling were generated using the Second Simulation of a Satellite Signal in the Solar Spectrum (6S) Radiative Transfer Model (RTM) simulation with MODerate Resolution Imaging Spectroradiometer (MODIS) BRDF product. Then, we randomly selected data according to the number of observations from 4 to 35 in the input dataset and performed BRDF modeling using them. Finally, the uncertainty was calculated by comparing reproduced surface reflectance through the BRDF model and simulated surface reflectance using 6S RTM and expressed as bias and root-mean-square-error (RMSE). The bias was negative for all observations and channels, but was very small within 0.01. RMSE showed a tendency to decrease as the number of observations increased, and showed a stable value within 0.05 in all channels. In addition, our results show that when the viewing zenith angle is 40° or more, the RMSE tends to increase slightly. This information can be utilized in the uncertainty analysis of subsequently retrieved geophysical variables.

• Structural Engineering and Mechanics
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• 제63권6호
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• pp.837-846
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• 2017

An accurate calculation of the stochastic wind field is the foundation for analyzing wind-induced structure response and reliability. In this research, the spatial correlation of structural wind field was considered based on the time domain method. A method for calculating the stochastic wind field based on cross stochastic Fourier spectrum was proposed. A flowchart of the proposed methodology is also presented in this study to represent the algorithm and workflow. Along with the analysis of regional wind speed distribution, the wind speed time history sample was calculated, and the efficiency can therefore be verified. Results show that the proposed method and programs could provide an efficient simulation for the wind-induced structure response analysis, and help determine the related parameters easily.