• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.83-90
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• 2009

A new IRF (Impulse Response Function) analysis technique in high resolution SAR image is presented by taking into account the real clutter environment. In order to investigate the realistic effect of clutter background on the impulse response function of SAR image, an ideally generated impulse response function is superimposed with a large number of background clutter data which are extracted from the various regions of an actual SAR image. As a performance measure, PSLR (Peak Sidelobe Ratio) of the clutter-contained IRF is presented in the various groups of clutter background, and finally the results are compared with the stochastic model.

• 대한원격탐사학회지
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• 제24권2호
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• pp.99-106
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• 2008

영상 레이다(SAR)는 주야간, 일조량에 관계없이 전천후로 영상획득이 가능하여 군사용으로는 물론 과학 민수용으로 광범위하게 활용된다. SAR 시스템에서는 고도, 운용 주파수, PRF 등의 다양한 시스템설계 파라미터로부터 생성된 임펄스 응답 함수(impulse response function)를 분석하여 공간해상도, PSLR, ISLR 등 영상품질 성능 파라미터의 추정이 가능하다. 그러나 모델링된 임펄스 응답 특성은 주변 클러터 환경이 고러되지 않은 이상적인 경우이므로 실제 주변 클러터 환경을 고려한 SAR 영상품질 분석 기법이 필요하다. 본 논문에서는 먼저 주요 SAR시스템 파라미터를 기반으로 SAR 점표적 원시 데이터를 생성하고, 거리-도플러 알고리듬(range-Doppler algorithm)을 이용하여 임펄스 응답 데이터를 형성한다. 그리고 실제 SAR영상의 일부분을 추출하여 주변 배경 클러터 환경 데이터를 형성한 후, 임펄스 응답 데이터를 삽입한다. 형성된 응답 데이터는 영상품질의 정확도를 향상시키고자 확장보간법을 도입하여 분석하고, 이에 대한 효과를 주요 도플러 파라미터인 방위 FM율 오차에 따른 성능분석을 수행함으로써 확인한다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.53-64
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• 2011

The present study considers multi-level approach for the analysis of parametric roll phenomena. Three kinds of computation method, GM variation, impulse response function (IRF), and Rankine panel method, are applied for the multi-level approach. IRF and Rankine panel method are based on the weakly nonlinear formulation which includes nonlinear Froude-Krylov and restoring forces. In the computation result of parametric roll occurrence test in regular waves, IRF and Rankine panel method show similar tendency. Although the GM variation approach predicts the occurrence of parametric roll at twice roll natural frequency, its frequency criteria shows a little difference. Nonlinear roll motion in bichromatic wave is also considered in this study. To prove the unstable roll motion in bichromatic waves, theoretical and numerical approaches are applied. The occurrence of parametric roll is theoretically examined by introducing the quasi-periodic Mathieu equation. Instability criteria are well predicted from stability analysis in theoretical approach. From the Fourier analysis, it has been verified that difference-frequency effects create the unstable roll motion. The occurrence of unstable roll motion in bichromatic wave is also observed in the experiment.

• The Journal of Asian Finance, Economics and Business
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• 제8권5호
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• pp.913-921
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• 2021

The objective of the study is to investigate the impact of the COVID-19 pandemic on Saudi Arabia stock market. The study relied on the data of the daily closing stock market price index Tadawul All Share Index (TASI), and the number of daily cases infected with COVID-19 during the period from March 15, 2020, to August 10, 2020. The study employs the Vector Auto-Regressive (VAR) model, the Impulse Response Function (IRF) and Autoregressive Conditional Heteroscedasticity (ARCH) models. The results of the correlation matrix and the Impulse Response Function (IRF) show that stock market returns responded negatively to the growth in COVID-19 infected cases during the pandemic. The results of ARCH model confirmed the negative impact of COVID-19 pandemic on KSA stock market returns. The results also showed that the negative market reaction was strong during the early days of the COVID-19 pandemic. The study concluded that stock market in KSA responded quickly to the COVID-19 pandemic; the response varies over time according to the stage of the pandemic. However, the Saudi government's response time and size of the stimulus package have played an important role in alleviating the impacts of the COVID-19 pandemic on Saudi Arabia Stock Market.

• 한국항공우주학회지
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• 제44권2호
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• pp.131-138
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• 2016

본 논문에서는 SAR (Synthetic Aperture Radar)에 사용되는 광대역 첩 신호에 대한 IRF(Impulse Response Function) 성능을 분석하였다. 영상 레이더의 첩 신호에서 영상품질에 크게 영향을 주는 인자는 진폭과 위상으로 크게 분류할 수 있다. 이 값들을 2차 다항식 커브 피팅을 사용하여 선형, 직교, 랜덤 그리고 리플 이득으로 구분할 수 있다. 본 연구에서는 이러한 인자들에 의한 IRF 영향을 분석하고, PSLR(Peak Side Lobe Ratio) 및 ISLR(Integrated Side Lobe Ratio)의 규격을 만족하기 위한 RF 비선형성에 의한 오차 값들의 최소치를 제안하였다.

• 대한조선학회논문집
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• 제49권1호
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• pp.60-67
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• 2012

This study considers the numerical analysis on parametric roll for container ships. As a method of numerical simulation, an impulse-response-function approach is applied in time domain. A systematic study is carried out for the parametric roll of two container ships, particularly observing the sensitivity of computational results to some parameters which can affect the analysis of parametric roll. The parameters to be considered are metacentric height (GM), simulation time window, and the discretization of wave spectrum. Based on the result of parametric roll simulation, numerical sensitivity and uncertainty in computational analysis are discussed.

• 한국전자파학회논문지
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• 제29권2호
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• pp.118-127
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• 2018

본 논문에서는 합성개구레이다(Synthetic Aperture Radar: SAR) 장비의 성능 분석을 위하여 레이다 표적모의장치를 설계, 제작한 결과를 선보인다. 먼저 표적모의장치의 기능과 성능에 대해 설명하고, SAR 장비와 연동하기 위한 표적 시나리오 생성방법에 대해 설명하였다. 또한 제작된 표적모의장치를 이용하여 SAR 장비의 시간지연 값을 간단하고 정확하게 측정하고 보상하는 방법을 개발하였다. 시간지연이 보상된 SAR 장비와 표적모의장치를 이용하여 SAR 영상에서 점표적을 획득하고, IRF(Impulse Response Function) 분석을 통해 성능을 분석하였다. 그 결과, 방위방향 IRF의 PSLR(Peak to Side Lobe Ratio)은 -13.25 dB, 해상도는 0.49 m로 이론값과 매우 유사한 값을 보였다.

• 대한조선학회논문집
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• 제52권3호
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• pp.187-197
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• 2015

This study aims the development of a semi-analytic method for the parametric roll of large containerships advancing in longitudinal waves. A 1.5 Degree-of-Freedom(DOF) model is proposed to account the change of transverse stability induced by wave elevations and vertical motions (heave and pitch). By approximating the nonlinearity of restoring moment at large heel angles, the magnitude of roll amplitude is predicted as well as susceptibility check for parametric roll occurrence. In order to increase the accuracy of the prediction, the relationship between righting arm(GZ) and metacentric height(GM) is examined in the presence of incident waves, and then a new formula is proposed. Based on the linear approximation of the mean and first harmonic component of GM, the equation of parametric roll in irregular wave excitations is introduced, and the computational results of the proposed model are validated by comparing those of weakly nonlinear simulation based on an impulse-response-function method combined with strip theory. The present semi-analytic doesn’ t require heavy computational effort, so that it is very efficient particularly when numerous sea conditions for the analysis of parametric roll should be considered.

• 지식경영연구
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• 제19권2호
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• pp.1-19
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• 2018

This study aims to identify the causal relationship among public technology transfer, technological performance, and research and development (R&D) productivity. Using the impulse-response function(IRF) of a panel vector autoregressive model (panel VAR), this study suggests the results of how long the factors such as technological performance (patent), public technology transfer, and R&D productivity takes and lasts if a one-unit shock of standard deviation occurs. As a result, first, the increase of public technology transfer activities has no power to increase the technology performance but improve the R&D productivity. If the public institute increases its technology transfer activities by one unit, the R&D productivity will increase within five years. Second, the impact of increasing technological performance on improvement of public technology transfer and R&D productivity is an insignificant. Third, the effect of R&D productivity on the public technology transfer creates a substantial reaction after a current time. Considering the structural relationships among public technology transfer, technological performance, and R&D productivity, if policy makers intend to construct the active R&D circumstance, technology suppliers should be motivated to run the active R&D mechanism because they achieve gains.

• 한국항공우주학회지
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• 제43권5호
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• pp.466-471
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• 2015

본 논문에서는 광역 관측을 위하여 새롭게 제안되고 있는 TOPS SAR 운용기법에 대한 모드 설계 및 성능 분석을 수행하였다. TOPS 모드는 기존 ScanSAR 모드의 단점인 scalloping을 개선하기 위하여 새롭게 제안된 모드로서, SAR 진행방향으로 안테나 빔을 조향하면서 영상 데이터를 획득하는 새로운 SAR 영상 획득 기술이다. 본 논문에서는 TOPS 모드에 대한 기술적 운용 개념을 소개하고, SAR 운용 변수를 추출하기 위한 모드 설계 결과를 제시한다. 또한 설계된 모드 변수를 이용하여 SAR 주요 성능인 IRF, NESZ, 및 DTAR을 분석하여 제시한다.