• 한국군사과학기술학회지
• /
• 제11권3호
• /
• pp.19-29
• /
• 2008

Underwater acoustic(UWA) communication is one of the most difficult field in terms of severe channel environments such as multipath propagation, high temporal and spatial variability of channel conditions. Therefore, it is important to model and analyze the characteristics of underwater acoustic channel such as multipath propagation, transmission loss, reverberation, and ambient noise. In this paper, UWA communication channel is modeled with a ray tracing method and applied to image transmission. Quadrature phase shift keying(QPSK) and multichannel decision feedback equalizer(DFE) are utilized as phase-coherent modulation method and equalization technique, respectively. The objective is to improve the performance of the image transmission using vertical sensor array instead of single sensor in the viewpoint of bit error rate(BER), constellation diagram, and received image quality.

• Current Optics and Photonics
• /
• 제1권4호
• /
• pp.336-343
• /
• 2017

A wide field-of-view (FOV) image contains more visual information than a conventional image. This study proposes a new type of hyperbolic mirror for wide FOV image acquisition. The proposed mirror consists of a hyperbolic cylindrical section and a bowl-shaped hyperbolic omnidirectional section. Using an imaging system with this mirror, it is possible to achieve a $213.8^{\circ}$ horizontal and a $126.94^{\circ}$ vertical maximum FOV. Parameters of each section of the mirror are designed to be continuous at the junction of the two parts, and the resultant image is seamless. The image-acquisition model is obtained using ray-tracing optics. To rectify the geometrical distortion of the original image due to the mirror, an image-restoration algorithm based on conformal projection is presented in this study. The performance of the proposed imaging system with the hyperbolic mirror and its image-restoration algorithm are verified by experiments.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
• /
• pp.110-113
• /
• 2004

Underwater acoustic(UWA) communication is one of the most difficult field because of several factors such as multipath propagation, high temporal and spatial variability of channel conditions. Therefore, it is important to model and analyze the characteristics of underwater acoustic channel such as multipath propagation, transmission loss, reverberation, and ambient noise. In this paper, UWA communication channel is modeled with a ray tracing method and applied to image transmission. Quadrature phase shift keying(QPSK) and multichannel decision feedback equalizer(DFE) are utilized as phase-coherent modulation method and equalization technique, respectively. The objective is to improve the performance of vertical sensor array than that of single sensor in the viewpoint of bit error rate(BER), constellation output, and received image quality.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
• /
• pp.888-890
• /
• 2003

The objective of this investigation is to establish a simple yet effective block adjustment procedure for the orthorectification of multi-orbit satellite images. The major works of the proposed scheme are: (1) adjustment of satellite‘s orbit accurately, (2) calculation of the error vectors for each tie point using digital terrain model and ray tracing technique, (3) refining the orbit using the Least Squares Filtering technique and (4) generation of the orthophotos. In the process of least squares filtering, we use the residual vectors on ground control points and tie points to collocate the orbit. In orthorectification, we use the indirect method to generate the orthoimage. Test areas cover northern Taiwan. Test images are from SPOT 5 satellite. Experimental results indicate that proposed method improves the relative accuracy significantly.

• 한국멀티미디어학회논문지
• /
• 제18권1호
• /
• pp.9-16
• /
• 2015

Various approaches to process active sonar signals are under study, but there are many problems to be considered. The sonar signals are distorted by the underwater environment, and the spatio-temporal and spectral characteristics of active sonar signals change in accordance with the aspect of the target even though they come from the same one. And it has difficulties in collecting actual underwater data. In this paper, we synthesized active target echoes based on ray tracing algorithm using target model having 3-dimensional highlight distribution. Then, Fractional Fourier transform was applied to synthesized target echoes to extract feature vector. Recognition experiment was performed using probabilistic neural network classifier.

• 한국해안해양공학회지
• /
• 제8권3호
• /
• pp.236-245
• /
• 1996

심해파가 천이수역 또는 천해로 이동하여 올 때 수심의 변화에 의해 발생하는 파의 굴절을 울산만 해역에서 수치모델을 이용하여 분석하여 보았다. 또한 이 모델은 해안 또는 연안의 어 특정한 지점에서 풍향 및 풍속 자료를 이용하여 파랑스책트럼을 계산할 수 있으며, 이로부터 그 지점에서의 유의파고를 구할 수 있다. 본 연구에서는 임의의 일정한 풍향과 풍속을 토대로 파랑스책트럼을 계산하였으며, 그 결과를 PNJ(Pierson, Newmann and James) 계산도표 및 Bretschneider 계산도표와 비교하여 보았다. 이러한 굴절과 파랑스책트럼은 항만 선정이나 각종 해안구조물 설계 등에 있어 기초자료로 유용하게 쓰일 수 있을 것이다

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
• /
• pp.49.3-49.3
• /
• 2009

Geostationary Ocean Colour Imager (GOCI) is the first ocean color instrument that will be operating in a geostationary orbit from 2010. GOCI will provide the crucial information of ocean environment around the Korean peninsula in high spatial and temporal resolutions at eight visible bands. We report an on-going development of imaging and radiometric performance prediction model for GOCI with realistic data for reflectance, transmittance, absorption, wave-front error and scattering properties for its optical elements. For performance simulation, Monte Carlo based ray tracing technique was used along the optical path starting from the Sun to the final detector plane for a fixed solar zenith angle. This was then followed by simulation of red-tide evolution detection and their radiance estimation, following the in-orbit operational sequence. The simulation results proves the GOCI flight model is capable of detecting both image and radiance originated from the key ocean phenomena including red tide. The model details and computational process are discussed with implications to other earth observation instruments.

• 한국광학회지
• /
• 제18권6호
• /
• pp.432-440
• /
• 2007

LCD 백라이트에 사용되는 집광필름의 광학적 성능을 예측하는 효율적인 방법으로 광선추적기법이 적용된 광학 시뮬레이션이 많이 사용되고 있다. 집광필름의 광특성을 정확히 예측하기 위해서는 시뮬레이션에 영향을 미치는 조건들을 세심하게 설정하여야 한다. 본 연구에서는 가장 대표적인 집광필름인 프리즘필름의 시야각 특성 및 휘도상승률에 중요한 영향을 미치는 시뮬레이션 조건을 분석하기 위해 반사필름, 가상의 평면광원, 프리즘필름으로 구성된 간단한 BLU 모델을 구성한 후 다양한 조건 하에서 체계적인 시뮬레이션을 수행하였다. 그 결과 (1) 집광필름의 구조 및 재질 변화에 따른 광학적 성능, 특히 휘도상승률의 상대적 변화는 위에서 기술한 간단한 모델로도 충분히 예측할 수 있음을 확인하였고, (2) 집광필름의 시야각 특성을 정확히 예측하기 위해서는 반사필름의 반사성격 및 집광필름에 입사되는 빛의 분포를 시뮬레이션에 정확히 반영해야만 함을 확인할 수 있었다. 확산판, 확산필름 및 프리즘필름이 적층된 직하형 BLU에서 얻어진 실험결과와 시뮬레이션 결과를 비교 분석한 결과, 상기의 시뮬레이션 모델에 반사필름이 보이는 양방향반사분포함수를 적용하고 확산필름 위의 출광분포를 광원으로 이용할 경우 실험에서 얻어진 프리즘필름 위의 출광분포를 정확히 재현할 수 있음을 확인하였다.

• 한국정보통신학회논문지
• /
• 제17권11호
• /
• pp.2505-2511
• /
• 2013

수중환경 하에서 표적을 탐지하고 식별하는 문제는 군사적인 목적은 물론 비군사적 목적으로도 많은 연구가 수행되어 왔다. 수중환경에서의 수중음향 신호가 시간 공간적으로 특성이 변화하며 천해 다중경로 환경을 반영하는 복잡한 특성을 보이는 점으로 인해 능동 표적인식 기술은 매우 어려운 기술로 여겨져 왔다. 또한 실제 데이터 수집의 어려움이 따르게 된다. 본 논문에서는 3차원 하이라이트 분포를 가지는 모델을 이용하여, 능동소나 표적신호를 음선 추적기법을 기반으로 하여 합성하였다. 합성된 표적신호를 대상으로 Fractional Fourier 변환을 적용하여 특징벡터를 추출하였고, 신경회로망 인식기를 이용하여 인식 실험을 수행하였다.

• 천문학회지
• /
• 제43권5호
• /
• pp.169-181
• /
• 2010

We develop a proto-model of an off-axis reflective telescope for infrared wide-field observations based on the design of Schwarzschild-Chang type telescope. With only two mirrors, this design achieves an entrance pupil diameter of 50 mm and an effective focal length of 100 mm. We can apply this design to a mid-infrared telescope with a field of view of $8^{\circ}{\times}8^{\circ}$. In spite of the substantial advantages of off-axis telescopes in the infrared compared to refractive or on-axis reflective telescopes, it is known to be difficult to align the mirrors in off-axis systems because of their asymmetric structures. Off-axis mirrors of our telescope are manufactured at the Korea Basic Science Institute (KBSI). We analyze the fabricated mirror surfaces by fitting polynomial functions to the measured data. We accomplish alignment of this two-mirror off-axis system using a ray tracing method. A simple imaging test is performed to compare a pinhole image with a simulated prediction.