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성세현,김석환,류동옥,홍진석,Seong, Sehyun,Kim, Sug-Whan,Ryu, Dongok,Hong, Jinsuk,Lockwood, Mike 한국천문학회 2012 天文學會報 Vol.37 No.2
The on-orbit test simulation for predicting the instrument directional responsivity was conducted by the Monte Carlo based integrated ray tracing (IRT) computation technique and analytic flux-to-signal conversion algorithms. For the on-orbit test simulation, the Sun model consists of the Lambertian scattering sphere and emitting spheroid rays, the Amon-Ra instrument is a two-channel including a broadband scanning radiometer (energy channel) and an imager with ${\pm}2^{\circ}$ FOV (visible channel). The solar radiation produced by the Sun model is directed to the instrument viewing port and traced through the dual channel optical train. The instrument model is rotated on its rotation axis and this gives a slow scan of the Sun model over the full field of view. The direction of the incident lights are fed with scanned images obtained from the visible channel instrument. The instrument responsivity was computed by the ratio of the incident radiation input to the instrument output. In the radiometric simulation, especially, measured BRDF of the 3D CPC was used for scattering effects on radiometry. With diamond turned 3D CPC inner surface, the anisotropic surface scattering model from the measured data was applied to ray tracing computation. The technical details of the on-orbit test simulation are presented together with field-of-view calibration plan.
유진희,김석환,Yu, Jinhee,Kim, Sug-Whan 한국천문학회 2012 天文學會報 Vol.37 No.2
Using Fresnel reflection and Hapke BRDF model with Apollo 10084 soil sample's scattering properties, we constructed a real scale optical lunar model and used it to simulate lunar apparent albedo and moonshine. For Fresnel reflection, the refractive index of $1.68{\pm}0.5$ was used. For Hapke BRDF parameters from BUGs BRDF measurement, the single scattering with w=0.33, hot spot width h=0.017, average phase angle ${\zeta}$=-0.086 and Legendre polynomial coefficients b=0.308, c=0.425 in wavelength 700nm with two types of Henyey-Greenstein phase function was applied. The computation model includes the Sun as a Lambertian scattering sphere, emitting 1.5078 W/m2 at 700nm in wavelength. The Sun and Moon models were then imported into the IRT based radiative transfer computation. The trial simulation of the irradiance levels of moonshine lights shows that they agree well with the ROLO measurement data. We then estimate the lunar apparent albedo to 0.11. The results are to be compared with the measurement data.
양슬기,이혜영,전진아,김석환,이직,박일흥,Yang, Seul Ki,Lee, Hye-Young,Jeon, Jina,Kim, Sug-Whan,Lee, Jik,Park, Il H. 한국천문학회 2012 天文學會報 Vol.37 No.2
We report technique used for improved measurement uncertainties for Photon detection efficiency(PDE) of $1mm^2$ single pixel SiPM. It consists of 470nm LED light source, two 2-inch integrating sphere and two NIST calibrated silicon photodiodes that have ${\pm}2.4%$ calibration error. With raytracing simulation of our experimental setup, we predict number of photon into SiPM and measurement uncertainty. For MPPC, Hamamatsu suggested PDE(1600 micro pixel) including crosstalk and afterpulse is 23.5% at 470 nm. By using new low calibration error photodiode and raytracing simulation, our simulation result has ${\pm}3%$ measurement uncertainty. The technical detail of measurement, simulation are presented with the results and implication.
이현수,양호순,이윤우,김석환,Yi, Hyun-Su,Yang, Ho-Soon,Lee, Yun-Woo,Kim, Sug-Whan 한국광학회 2008 한국광학회지 Vol.19 No.6
본 논문에서는 툴 영향 함수(Tool Influence Function)를 이용한 피치(pitch)툴의 정량적 물질 제거 제어 기법에 대하여 기술하였다. 피치 툴은 뛰어난 표면 거칠기를 생성시키는 반면 툴의 물질 변형이 상대적으로 크고 물질제거가 어렵기 때문에 일반적으로 숙련된 가공 기술자에 의한 정성적 연마 기법으로 간주되었다. 하지만 이러한 피치 툴을 이용한 수치모사 및 실험을 수행한 결과, 정량적 피치 툴 연마 기법이 가능하다는 것을 알 수 있었다. 실험과 수치모사에 의한 물질 제거 형상은 약 79%의 정확도로 일치하였다. 또한 직경 280 mm의 평면가공에 대한 수치모사 단계에서 5번의 모의 가공 후 p-v(peak to valley) $1{\mu}m$의 최초 형상오차를 168 nm까지 낮추는 결과를 얻을 수 있었다. The pitch tool provides superior surface roughness compared to other types of polishing tool. However, because of difficulty in handling the pitch tool, pitch tool polishing has rarely been analysed, which led many craftsman to eliminate the pitch tool from their experiences. We found that it was possible to use a pitch tool in the well-determined material removal after the completion of computer simulation and experiment. We could simulate the TIF of the pitch tool with 79% accuracy. Also, after five successive simulations of polishing process on a 280 mm optical flat, the surface p-v error was found to be reduced from $1{\mu}m$ to 168 nm.
The Slewing Mirror Telescope of the Ultra Fast Flash Observatory Pathfinder
정수민,최지녕,정애라,김민빈,김석환,김예원,김지은,이직,임희진,나고운,남지우,박일흥,서정은,Jeong, Soomin,Choi, Ji Nyeong,Jung, Aera,Kim, Min Bin,Kim, Sug-Whan,Kim, Ye Won,Kim, Jieun,Lee, Jik,Lim, Heuijin,Na, Go Woon,Nam, Jiwoo,Park, Il Hung 한국천문학회 2012 天文學會報 Vol.37 No.2
The Slewing Mirror Telescope (SMT) is a key telescope of Ultra-Fast Flash Observatory (UFFO) space project to explore the first sub-minute or sub-seconds early photons from the Gamma Ray Bursts (GRBs) afterglows. The first realization of UFFO is the 20kg UFFO-Pathfinder (UFFO-P) to be launched on board the Russian Lomonosov satellite in 2013 by the Soyuz-2 rocket. Once the UFFO Burst Alert & Trigger Telescope (UBAT) detects the GRBs, Slewing mirror (SM) will rotate to bring the GRB into the SMT's field of view instead of slewing the entire spacecraft. SMT can image the UV/Optical counterpart with about 4-arcsec accuracy. However it will provide a important understanding of the GRB mechanism by measuring the sub-minute optical photons from GRBs. SMT can respond to the trigger over $35^{\circ}{\times}35^{\circ}$ wide field of view within 1 sec by using Slewing Mirror Stage (SMS). SMT has 10-cm Ritchey-Chretien telescope and $256{\times}256$ pixilated Intensified Charge-Coupled Device (ICCD) on focal plane. In this paper, we discuss the overall design of UFFO-P SMT instrument and payloads development status.
장거리 화염 탐지용 적외선 카메라 성능 광선추적 수치모사
윤지연,류동옥,김상민,성세현,윤웅섭,김지은,김석환,Yoon, Jeeyeon,Ryu, Dongok,Kim, Sangmin,Seong, Sehyun,Yoon, Woongsup,Kim, Jieun,Kim, Sug-Whan 한국광학회 2014 한국광학회지 Vol.25 No.5
본 논문에서는 사거리가 수백 km에 이르는 장거리 미사일의 화염을 발사 초기에 탐지할 수 있는 적외선 카메라에 대한 현실적 영상성능 수치모사 결과를 제시한다. 적외선 카메라는 중적외선 대역용 다수의 렌즈로 구성된 굴절식 광학계이다. 관측대상과 배경의 모델링 전체를 포함하는 규모의통합적 광선추적을 수행함으로 카메라를 통해 보는 영상과 검출기에 도달하는 빛의 세기에 대한 정보를 획득하였다. 관측대상이 되는 미사일 화염의 방사휘도(radiance)는 CFD 타입의 복사전달 기법으로 계산하였으며 이를 광원으로 삽입하여 광선추적을 수행하였다. 관측배경이 되는 대기 모델은 MODTRAN을 사용하여 열복사의 경로, 단일/다중 산란 복사와 투과율을 계산하였다. 광선추적 수치모사의 결과로써 관측대상의 이미지와 도달한 복사전달 성능(radiometric performance)의 검증을 통해 적외선 카메라가 요구사항을 만족함을 입증하였다. We report a realistic field-performance simulation for a new MWIR camera. It is designed for early detection of missile plumes over a distance range of a few hundred kilometers. Both imaging and radiometric performance of the camera are studied by using real-scale integrated ray tracing, including targets, atmosphere, and background scene models. The simulation results demonstrate that the camera would satisfy the imaging and radiometric performance requirements for field operation.
오은송,강혁모,현상원,김건희,박영제,최종국,김석환,Oh, Eunsong,Kang, Hyukmo,Hyun, Sangwon,Kim, Geon-Hee,Park, YoungJe,Choi, Jong-Kuk,Kim, Sug-Whan 한국광학회 2015 한국광학회지 Vol.26 No.3
본 논문에서는 연안 지역 저고도 원격측정을 위한 소형 무인항공기 용 초분광센서 개발의 일환으로 비축 삼반사경 전단광학계의 설계와 성능분석 결과를 제시하였다. 이 광학계는 수 cm의 공간해상도(4cm@500m 운영고도)와 $4^{\circ}$의 시야각, 그리고 신호대 잡음비 100(@660 nm) 이상의 요구사항을 만족시키기 위하여, 70 mm의 입사동 크기와 개구수 5.0으로 설계 사양을 가지는 비구면의 주경과 부경이 포함된 비축 삼반사경 형태로 설계되었다. 본 설계의 광학성능은 $1/15{\lambda}$ 이하 RMS 파면오차 성능과 0.75이상의 MTF 성능(@660 nm)이 기대된다. 제작과 조립 단계를 고려하여 민감도 분석을 통해 3 반사경을 정렬 보상자로 선정하였으며, 경사 공차범위는 요소별로 0.17 mrad 으로 결정되었다. 이 비축 삼반사경 광학설계는 기존 초분광센서의 전단광학계에 비해 높은 광학성능을 보이고, 소형 무인항공기에 맞추어 경량화가 가능하도록 제작 기반을 설정하여, 향후 연안 원격탐사 연구에 활용될 예정이다. We report the design and performance analysis of an off-axis three-mirror telescope as the fore optics for a new hyperspectral sensor aboard a small unmanned aerial vehicle (UAV), for low-altitude coastal remote sensing. The sensor needs to have at least 4 cm of spatial resolution at an operating altitude of 500 m, $4^{\circ}$ field of view (FOV), and a signal to noise ratio (SNR) of 100 at 660 nm. For these performance requirements, the sensor's optical design has an entrance pupil diameter of 70 mm and an F-ratio of 5.0. The fore optics is a three-mirror system, including aspheric primary and secondary mirrors. The optical performance is expected to reach $1/15{\lambda}$ in RMS wavefront error and 0.75 in MTF value at 660 nm. Considering the manufacturing and assembling phase, we determined the alignment compensation due to the tertiary mirror from the sensitivity, and derived the tilt-tolerance range to be 0.17 mrad. The off-axis three-mirror telescope, which has better performance than the fore optics of other hyperspectral sensors and is fitted for a small UAV, will contribute to ocean remote-sensing research.
The Electronics system of the Ultra Fast Flash Observatory Pathfinder
김지은,최지녕,최연주,정수민,정애라,김민빈,김석환,김예원,이직,임희진,민경욱,나고운,박일흥,서정은,Kim, Ji Eun,Choi, Ji Nyeong,Choi, Yeon Ju,Jeong, Soomin,Jung, Aera,Kim, Min Bin,Kim, Sug-Whan,Kim, Ye Won,Lee, Jik,Lim, Heuijin,Min, Kyung Wook,N 한국천문학회 2012 天文學會報 Vol.37 No.2
The Ultra Fast Flash Observatory (UFFO) pathfinder consists of the UFFO Burst Alert X-ray Trigger telescope (UBAT) and the Slewing Mirror Telescope (SMT). They are controlled by the UFFO Data Acquisition system (UDAQ). The UBAT triggers Gamma-Ray Bursts(GRBs) and sends the position information to the SMT. The SMT slews the motorized mirror rapidly to the GRB position to take the UV/Optical data within a second after trigger. The UDAQ controls each instrument, communicates with the satellite, collects the data from UBAT and SMT, and transfers them to the satellite. Each instrument uses its own field programmable gates arrays (FPGA) for low power consumption and fast processing, and all functions are implemented in FPGAs without using microprocessors. The entire electronics system of the UFFO pathfinder including architecture, control, and data flow will be presented.
최지녕,최연주,정수민,정애라,김민빈,김지은,김석환,김예원,이직,임희진,민경욱,나고운,남지우,박일흥,서정은,Choi, Ji Nyeong,Choi, Yeon Ju,Jeong, Soomin,Jung, Aera,Kim, Min Bin,Kim, Ji Eun,Kim, Sug-Whan,Kim, Ye Won,Lee, Jik,Lim, Heuijin,Min, Kyung Wo 한국천문학회 2012 天文學會報 Vol.37 No.2
UFFO Burst Alert & Trigger telescope (UBAT) is one of major instruments of UFFO-Pathfinder. The UBAT aims at 10 arcmin resolution localization of Gamma Ray Bursts with X-ray coded mask technique. It has $400mm{\times}400mm$ coded mask aperture, hopper, shielding and detector module with effective area of $191cm^2$. The detector module consists of an assembly of 36 64-ch MAPMTs and $25mm{\times}25mm$ pixellated YSO crystal array, and associated analog and digital electronics of about 2500 channels. We performed a vibration test using a dummy MAPMT with the detector module structure to measure the indused stress applied onto the MAPMT. We designed a sub-structure on the detector module to avoid the resonance that would otherwise deforms the detector module structure. A finite element analysis confirms the reduction of the load acceleration down to 12g. The experimental results are to be reported. Consequently, it proves that the MAPMT arrays of the flight UBAT detector module structure would survive in the space launch environment.