마리나 츠베타예바 후기 산문의 신화 시화 : 마리나 츠베타예바 시학의 상징주의적 경향

학위논문(석사)--서울대학교 대학원 :노어노문학과 노문학전공,2001.Maste

진화의학에 대한 고찰 : 전염병의 경우를 중심으로

학위논문(석사)--서울대학교 대학원 :의학과 의사학전공,2007.Maste

ISAR imaging using rear view of an automobile

MasterThis paper introduces the inverse synthetic aperture radar (ISAR) imaging technique for rear view target of an automobile, which uses both linear frequency modulation-frequency shift keying (LFM-FSK) waveform and monopulse tracking. The LFM-FSK waveform consists of two sequential stepped frequency waveforms with some frequency offset, and thus, can be used to generate ISAR images of rear view target of an automobile. However, ISAR images can be blurred due to following three factors, such as inter-pulse phase errors, inter-burst translational motion that defined as a target motion along radar line of sight (RLOS), and non-uniform change rate of relative aspect angle between the radar and targets. In order to obtain focused ISAR images, appropriate motion compensation should be applied. The motion compensation procedure can be divided into following three steps: removing inter-pulse phase errors using particle swarm optimization (PSO), translational motion compensation, rotational motion compensation using Lagrange interpolation. Simulation results show that the motion compensation technique mentioned above can effectively remove blurring of ISAR due to motion errors, and finally well focused ISAR images can be generated

ISAR Imaging of Non-Cooperative Targets in Complex Motions

DoctorUsually, the inverse synthetic aperture radar (ISAR) imaging problem is more challenging than synthetic aperture radar (SAR) imaging. In SAR, the well-controlled radar platform is usually known, whereas the target motion is usually unknown in ISAR system. Therefore, how to deal with unknown target motion is a critical issue in ISAR imaging. In this dissertation, we address major problems, caused by the non-cooperative characteristics of the target for ISAR imaging. When a target undergoes complex three-dimensional (3D) motions, focused ISAR images cannot be obtained using any motion compensation (MOCOM) algorithms. To address this problem, in chapter 2, we propose a method to efficiently determine the suitable frame time and length for ISAR imaging, which exploits phase nonlinearity and discrete polynomial phase transforms. Once suitable frame times are effectively determined, we should perform MOCOM to remove undesired target motions. However, conventional ISAR MOCOM schemes are not optimal, in terms of reconstructed image and/or computation time. Motivated by the problems of the conventional schemes, in Chapter 3, we introduce an efficient autofocus chain for ISAR imaging of non-cooperative moving target. From the experimental results using real data sets, we can conclude that the proposed method is highly efficient to remove undesired motion errors, in terms of both image quality and computational efficiency. Focused ISAR image can be obtained in range-Doppler (RD) domain after applying frame-selection scheme and MOCOM. However, RD image is inefficient for target classification, due to the variable Doppler scaling factor related to target’s own rotational motion. Therefore, for more effective use of ISAR image, ISAR images should be rescaled in the homogeneous range and cross-range domain by estimating rotation velocity of a non-cooperative targets. In Chapter 4, we propose particle swarm optimization combined with exhaustive search method (PSO-ESM) for ISAR cross-range scaling (CRS). Robust scatterers against angular scintillation are extracted using scale invariant feature transform, and locations of the extracted scatterers are applied to PSO-ESM. We should note that the PSO-ESM enables to perform robust CRS by joint estimation of rotation center and velocity. Meanwhile, all aforementioned studies are related to monostatic radar configurations where a transmitter and a receiver are collocated. However, monostatic ISAR imaging suffers from some limitations, including geometrical issues and imaging problems with regard to stealthy targets. In a monostatic radar configuration, the aspect angle of a target does not change relative to the radar when the target moves along the radar line of sight (LOS). In this case, scatterers distributed on the target cannot be separated in the cross-range direction. In addition, the imaging of a stealthy target is difficult in this configuration because a stealthy target is designed to reflect electromagnetic energy to directions other than that of the radar, yielding a decrease in the signal-to-noise ratio (SNR) of a received radar signal. To overcome these problems, a bistatic radar configuration where the transmitter and receiver are spatially separated has been considered for ISAR imaging. Because the bistatic ISAR (Bi-ISAR) geometry provides adequate look-angle diversity of the target, rotation of the target with respect to the radar is ensured for the acquisition of the desired cross-range resolution. In addition, imaging of a stealthy target can be easily achieved using bistatic radars because the SNR of the received signal in the bistatc configurations increases compared with a monostatic radar. Therefore, recently, studies related to Bi-ISAR imaging has been widely studied. In Chapter 5, we introduce a bistatic inverse synthetic aperture radar (Bi-ISAR) CRS method to more effectively use Bi-ISAR images in their applications. We note that monostatic ISAR CRS method, presented in Chapter 4, cannot be applied in Bi-ISAR configurations. For this, we propose a method to estimate the effective rotation velocity of a target in a Bi-ISAR imaging system, and restore a linear-geometry distortion that yields a sheared shape of Bi-ISAR images. In the simulations, we observed that our proposed method is capable of performing robust and precise Bi-ISAR CRS. In addition, monostatic MOCOM approaches fails to provide focused ISAR images in bistatic radar configuration. To address this problem, in Chapter 6, a new MOCOM framework for Bi-ISAR imaging is proposed. In the proposed framework, the undesired motion errors can be correctly removed in Bi-ISAR systems, yielding focused Bi-ISAR images. In addition, restoration of the sheared Bi-ISAR images is achieved in the proposed framework. In the simulations and experiments, we found that the proposed Bi-ISAR MOCOM framework can provide high-quality Bi-ISAR images

후방 감시용 차량용 레이더를 이용한 ISAR 영상 형성

2

ISAR 영상에 대한 Sparse 복원 알고리즘 성능 비교

2

SIFT를 이용한 기동표적의 ISAR Cross-range scaling

2

RCS를 이용한 포탄 식별을 위한 퍼지 구분기의 최적화

2

Flexible metamaterial with Babinet principle band-pass behavior and subwavelength imaging

학위논문(석사) - 한국과학기술원 : 기계공학전공, 2012.8, [ iii, 34 p. ]최근 수십년 간 전자기 메타물질은 자연에서 얻을 수 없는 성질로 인해 많은 연구가 이루어져 왔다. 메타물질은 삽입된 금속구조물의 자유전자의 작용으로 자연에서 찾아볼 수 없는 음의 굴절률이나 클로킹 능력을 갖게 되었다. 테라헤르츠 주파수는 적당한 생성과 감지 장치가 미비하여 다양한 전자기파의 주파수 대역에 비해 덜 개척되어 있다. 전자기파는 여러 주파수 대역이 섞여 있는 경우가 많으므로 특정 주파수만을 걸러내는 필터는 과학과 공학 전반에 걸쳐 기초적인 소자로서 중요하다. 이 논문의 첫 절반은 테라헤르츠 대역투과 필터 연구결과를 소개한다. 기초가 되는 바비넷 원리, 전산모사 수치해석, 공정 과정과 순서, 샘플 측정 결과가 포함되어 있다. 또 다른 주파수는 우리 눈이 감지하는 중심대역인 광학 대역이다. 관심이 집중되고 있는 나노 규모의 과학은 나노 규모를 관찰할 수 있는 장치가 필요하다. 이 논문의 마지막 절반은 탄소나노튜브를 틀로 사용하여 파장 이하 규모의 물체를 이미징하는 연구를 소개한다. 관련된 표면플라즈몬 이론, 전산모사 수치해석, 그리고 측정 결과가 포함되어 있다.한국과학기술원 : 기계공학전공