• Journal of Astronomy and Space Sciences
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• 제31권3호
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• pp.241-246
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• 2014

The Amon-Ra instrument is the main optical payload of the proposed EARTHSHINE satellite. It consists of a visible wavelength instrument and an IR energy channel instrument to measure a global Earth albedo. We report a new sensitivity technique for efficient alignment of the visible channel instrument. Whilst the sensitivity table method has been widely used in the alignment process, the straightforward application of the method tends to produce slow process convergence because of shop floor alignment practice uncertainties. We investigated the error sources commonly associated with alignment practices and used them when estimating the Zernike polynomial coefficients. Aided with single center field wavefront error (WFE) measurements and their corresponding Zernike polynomial coefficients, the method involves the construction and use of an experimental, instead of simulated, sensitivity table to be used for alignment state estimations. A trial alignment experiment for the Amon Ra optical system was performed and the results show that 71.28 nm in rms WFE was achieved only after two alignment iterations. This tends to demonstrate its superior performance to the conventional method.

• Journal of Astronomy and Space Sciences
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• 제19권4호
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• pp.319-326
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• 2002

인공위성의 본체 및 탑재체 제작에 사용되고 있는 구성품 재질 12점을 수집하여 가시광 영역에서 지상 분광실험을 수행한 결과 위성체 구성품 재질별로 분광반사율과 분광유형이 뚜렷이 차이를 보였고 위성체의 재질별 분류 및 식별이 가능하였다. 인공위성 재질의 지상 분광실험 결과는 운용초기에 있는 인공위성이나 우주잔해물을 실제로 분광관측하여 얻은 자료와 비교함으로써 대상물의 재질유형 및 재질구성비, 그리고 크기와 중량을 예측하는데 활용될 수 있을 것이다.

• 한국지리정보학회지
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• 제6권2호
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• pp.1-9
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• 2003

해상에서 1997년 1월부터 12월까지 맑은 날과 구름이 많은 대기상태에서 GMS-5에 장착된 VISSR(visible and infrared spin scan radiometer) 자료를 이용하여 $5km{\times}5km$ 격자의 공간 분해능에서 태양복사를 추정하였다. 섬에 설치되어 있는 기상청의 pyranometer 자료로 추정 일사량을 검증하였다. 추정된 시간별 일사량의 RMSE(root mean square error)는 $104W/m^2$이고, 상관계수는 0.91이었다. 한반도 부근의 해상에서 조사된 시간별 태양복사의 최대값은 황해와 동해에서 6월에 타나고, 남해에서는 8월에 나타나는데, 이는 6월에 저기압과 전선에 의한 기상 악화에 기인한다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.615-620
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• 2002

Probability distribution of the sea surface slope is estimated using sun glitter images derived from visible radiometer on Geostationary Meteorological Satellite (GMS) and surface vector winds observed by spaceborne scatterometers. The brightness of the visible images is converted to the probability of wave surfaces which reflect the sunlight toward GMS in grids of 0.25 deg $\times$ 0.25 deg. Slope and azimuth angle required for the reflection of the sun's ray toward GMS are calculated for each grid from the geometry of GMS observation and location of the sun. The GMS images are then collocated with surface wind data observed by three scatterometers. Using the collocated data set of about 30 million points obtained in a period of 4 years from 1995 to 1999, probability distribution function of the surface slope is estimated as a function of wind speed and azimuth angle relative to the wind direction. Results are compared with those of Cox and Munk (1954a, b). Surface slope estimated by the present method shows narrower distribution and much less directivity relative to the wind direction than that reported by Cox and Munk. It is expected that their data were obtained under conditions of growing wind waves. In general, wind waves are not always developing, and slope distribution might differ from the results of Cox and Munk. Most of our data are obtained in the subtropical seas under clear-sky conditions. This difference of the conditions may be the reason for the difference of slope distribution.

• Journal of Astronomy and Space Sciences
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• 제28권4호
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• pp.345-354
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• 2011

Earth acquisition is to solve when earth can be visible from satellite after Sun acquisition during launch and early operation period or on-station satellite anomaly. In this paper, the algorithm and test result of the Communication, Ocean and Meteorological Satellite (COMS) Earth acquisition are presented in case of on-station satellite anomaly status. The algorithms for the calculation of Earth-pointing attitude control parameters including those attitude direction vector, rotation matrix, and maneuver time and duration are based on COMS configuration (Eurostar 3000 bus). The coordinate system uses the reference initial frame. The constraint calculating available time-slot to perform the earth acquisition considers eclipse, angular separation, solar local time, and infra-red earth sensor blinding conditions. The results of Electronics and Telecommunications Research Institute (ETRI) are compared with that of the Astrium software to validate the implemented ETRI software.

• 대한원격탐사학회지
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• 제19권3호
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• pp.181-190
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• 2003

Since the operation of the first satellite-based navigation service, satellite positioning has played an increasing role in both surveying and geodesy, and has become an indispensable tool for precise relative positioning. However, in some situations, e.g. at a low angle of elevation, the use of satellites for navigation is seriously restricted because obstacles like buildings and mountains can block signals. As a mean to resolve this problem, the quasi-zenith satellite system has been proposed as a next-generation satellite navigation system. Quasi-zenith satellite is a system which simultaneously deploys several satellites in a quasi-zenith geostationary orbit so that one of the satellites always stay close to the zenith if viewed from a specific point on the ground of East Asia. Thus, if a position measurement function compatible with CPS is installed in the quasi-zenith and stationary satellites, and these satellites are utilized together with the CPS, four satellites can be accessed simultaneously nearly all day long and a substantial improvement in position measurement, especially in metropolitan areas, can be achieved. The purpose of this paper is to evaluate the effectiveness of quasi-zenith satellite system on positioning accuracy improvement through simulation by using precise orbital information of the satellites and a three-dimensional digital map. Through this developed simulation system, it is possible to calculate the number of simultaneously visible satellites and available area for positioning without the need of actual observation. Furthermore, this system can calculate the Dilution Of Precision (DOP) and the error distribution.

• 한국지구과학회:학술대회논문집
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• 한국지구과학회 2005년도 춘계학술발표회 논문집
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• pp.174-175
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• 2005

• 한국위성정보통신학회논문지
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• 제6권1호
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• pp.57-62
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• 2011

가시광 통신 시스템은 LED를 통해 방사되는 가시광을 이용한 차세대 통신 시스템으로, 유비쿼터스 네트워크 서비스 구축 시 에너지 절감 효과를 가져 올 수 있다. 또한 기존 인프라를 활용하여 고출력 전송이 가능하며 유지 보수 비용을 절감할 수 있다. 하지만 가시광 통신 시스템에서는 인접 송신기 간섭 신호의 영향으로 네트워크 경계에 위치한 수신기의 신호 검출 성능은 급격히 열화되고 전송 효율은 감소하게 된다. 본 논문에서는 광 빔포밍을 활용하는 경우, 송신기 간 간섭 완화 방안을 제시하고 그 수신 성능을 평가한다. 제안하는 광 빔포밍 방식은 사용하지 않는 기존 가시광 통신 시스템 대비 BER 측면에서 향상된 성능을 보이며, 평균 5~7dB 성능 개전을 가져온다.

• 한국위성정보통신학회논문지
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• 제7권3호
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• pp.63-68
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• 2012

가시광 통신 시스템은 LED를 통해 방사되는 가시광을 이용한 차세대 통신 시스템으로, 유비쿼터스 네트워크 서비스 구축 시 에너지 절감 효과를 가져 올 수 있다. 또한 기존 인프라를 활용하여 고출력 전송이 가능하며 유지 보수 비용을 절감할 수 있다. 하지만 가시광 통신 시스템에서는 인접 송신기 간섭 신호의 영향으로 네트워크 경계에 위치한 수신기의 신호 검출 성능은 급격히 열화되고 전송 효율은 감소하게 된다. 본 논문에서는 가시광 통신 시스템에서 다수의 Tx가 인접해 있을 때 발생하는 송신기간 간섭 문제를 광 릴레이와 광 빔포밍 기법 적용을 통하여 효율적으로 간섭을 완화하고 그 성능을 평가한다. 제안하는 시스템의 결과로 사용하지 않는 기존 가시광 통신 시스템 대비 BER 측면과 채널 용량에서 모의실험을 통하여 향상된 성능을 보인다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 1999년도 Proceedings of International Symposium on Remote Sensing
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• pp.227-230
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• 1999

Surface solar radiation over the sea is estimated using Visible and Infrared Spin Scan Radiometer data onbord Geostationary Meteorological Satellite(GMS) 5 for January, 1997 to December 1997 in clear and cloudy conditions. The hourly insolation is estimated with a spatial resolution of 5$\times$ 5 km grid. The island pyranometer belonging to the Japan Meteorological Agency is used for validation of the estimated insolation. It is shown that the estimated hourly insolation has RMSE(root mean square) error of 104 W/$m^2$. The variability of the hourly solar radiation was investigated on 3 areas over seas around Korean Peninsula. The solar radiation of East Sea is similar to Yellow Sea. The maximum value of solar radiation is on June of year. The maximum value in south sea is on August because weather is poor by low pressure and front in June