• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
• /
• pp.1261-1263
• /
• 2003

Based on twelve observational stations low meteorological visibility (LMV) data during November 2002 to April 2003, the spatial distribution of LMV over Hongkong area (113.8$^{\circ}$ E-114.4$^{\circ}$ E, 22.1$^{\circ}$ N-22.4$^{\circ}$ N) is studied, using a PCA method. Optical spectrum of NOAA-16 associated with LMV shows that the significant effect factors correlated with LMV in the leading mode are the difference or rate between the visible and near-IR channels and single visible channel. A successful retrieval of LMV is done and a regression equation with a multiple correlation coefficient of 0.67 is obtained.

• Journal of Astronomy and Space Sciences
• /
• 제26권2호
• /
• pp.199-210
• /
• 2009

다양한 위성항법시스템이 개발 중이지만 현재 측위에 사용 가능한 것은 GPS와 GLONASS 뿐이다. 이 연구에서는 GLONASS의 궤도력 중에서 방송궤도력을 이용하여, 위성의 운동을 나타내는 미분방정식을 4차 Runge-Kutta 방법으로 수치적분하여 위성궤도를 예측하고, 그 정 확도를 평가하였다. 생성한 예측지도는 정밀궤도력과 비교하여 정확도를 검증하였는데, 1일간의 예측궤도와 7일간의 예측제도의 3차원 최대오차는 각각 17.4km, 40.1km로 나타났으며, RMS 오차는 각각 14.3km, 15.7km로 나타났다. 또한 예측제도를 이용하여 산출한 가시위성의 개수와 실제관측 결과를 비교하였다. 그 결과, 관측지점의 주변 건물에 의한 영향으로 발생하는 차이를 제외하고 결과가 일치하는 것을 확인하였다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2008년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
• /
• pp.190-192
• /
• 2008

GNSS(Global navigation Satellite system) is the system which determines the users' position using the navigation satellites. The position determination using GNSS has to be always Possible to appling GNSS to railway system widely. Especially, to apply GNSS to the safety-critical application, such as train control system, the satellite's visibility has to be always secured. This study describes the necessity of visibility analysis and the method. And also the visibility analysis of the stand-alone GNSS and the integration GNSS are performed and the applicability of GNSS for train control application is analysed.

• 대한원격탐사학회지
• /
• 제23권4호
• /
• pp.311-321
• /
• 2007

해수 속으로 입수된 하향 태양에너지 (down-welling irradiance)가 수심이 깊어짐에 따라 확산 소산되는 정도를 나타내는 하향 확산 감쇠계수 (Diffuse attenuation coefficient of down-welling irradiance, $K_d({\lambda})$)와 해수 속에서의 가시거리를 나타내는 수중시계는 수중에서의 광학적 성격을 나타내는 중요한 지수이다. 이러한 $K_d({\lambda})$ 및 수중시계에 대한 많은 연구가 세계적으로 여러 해역에 대해 수행되어 왔지만 우리나라 연안 해역을 대상으로 하는 연구는 매우 적은 실정이다. 따라서 본 연구에서는 우리나라의 황해 중부해역을 대상으로 $K_d({\lambda})$ 및 수중시계를 관측하였고, 해색위성용 $K_d({\lambda})$ 및 수중시계 알고리즘을 개발하였다. $K_d({\lambda})$ 및 수중시계 관측을 위하여 2006년 9월 $19{\sim}22$일, 4일 동안 황해 중부해역에서 현장관측을 실시하였으며, 총 39개 정점에서 해양 광학적 자료와 해양 환경적 자료를 획득하였다. 획득된 자료를 이용하여 경험적 방법으로 $K_d({\lambda})$와 수중시계 알고리즘을 개발하였으며, 개발된 알고리즘들은 각각 기존의 대양의 자료를 이용하여 개발된 SeaWiFS 해색 센서용 $K_d({\lambda})$ 알고리즘과 NRL (Naval Research Laboratory)에서 개발된 SeaWiFS 센서용 수중시계 알고리즘과 비교하여 보았다. $K_d({\lambda})$ 알고리즘의 경우는 탁도가 높은 해역 값에서 약간의 차이를 보였으며, 수중시계 알고리즘의 경우 NRL의 알고리즘에 비해 약간 높은 계수 값을 얻었다.

• International Journal of Aeronautical and Space Sciences
• /
• 제17권1호
• /
• pp.89-100
• /
• 2016

Given the unpredictability of the space environment, satellite communications are manually performed by exchanging telecommands and telemetry. Ground support for orbiting satellites is given only during limited periods of ground antenna visibility, which can result in conflicts when multiple satellites are present. This problem can be regarded as a scheduling problem of allocating antenna support (task) to limited visibility (resource). To mitigate unforeseen errors and costs associated with manual scheduling and mission planning, we propose a novel method based on a genetic algorithm to solve the ground support problem of multiple satellites and antennae with visibility conflicts. Numerous scheduling parameters, including user priority, emergency, profit, contact interval, support time, remaining resource, are considered to provide maximum benefit to users and real applications. The modeling and formulae are developed in accordance with the characteristics of satellite communication. To validate the proposed algorithm, 20 satellites and 3 ground antennae in the Korean peninsula are assumed and modeled using the satellite tool kit (STK). The proposed algorithm is applied to two operation modes: (i) telemetry, tracking, and command and (ii) payload. The results of the present study show near-optimal scheduling in both operation modes and demonstrate the applicability of the proposed algorithm to actual mission control systems.

• 한국측량학회지
• /
• 제27권2호
• /
• pp.119-127
• /
• 2009

다양한 차세대 위성항법시스템들이 개발되고 있지만, 현재 사용자가 측위에 이용할 수 있는 위성항법시스템은 GPS와 GLONASS 뿐이다. 이 연구에서는 GLONASS의 궤도력 중에서 알마낙을 이용하여 위성궤도를 예측하고 예측궤도의 정확도를 평가하였다. 예측궤도를 생성하기 위하여 알마낙 파일에 포함되어 있는 케플러 궤도요소와 궤도방정식을 이용하였으며, 그 결과는 정밀궤도력과의 좌표 비교를 통하여 정확도를 검증하였다. 그 결과, 7일 동안 예측한 위성궤도의 3차원 최대오차는 155.4km로 나타났으며, RMS 오차는 56.3km로 나타났다. 또한 실제관측 결과와의 비교를 통해 궤도오차가 위성의 가시성을 분석하는데 무리가 없는 수준임을 확인하였다.

• Journal of Positioning, Navigation, and Timing
• /
• 제8권2호
• /
• pp.79-85
• /
• 2019

The mission tasks of polar exploration utilizing unmanned systems such as glacier monitoring, ecosystem research, and inland exploration have been expanded. To facilitate unmanned exploration mission tasks, precise and robust navigation systems are required. However, limitations on the utilization of satellite navigation system are present due to satellite orbital characteristics at the polar region located in a high latitude. The orbital inclination of global positioning system (GPS), which was developed to be utilized in mid-latitude sites, was designed at $55^{\circ}$. This means that as the user is located in higher latitudes, the satellite visibility and vertical precision become worse. In addition, the use of satellite-based wide-area augmentation system (SBAS) is also limited in higher latitude regions than the maximum latitude of signal reception by stationary satellites, which is $70^{\circ}$. This study proposes a local-area augmentation system that additionally utilizes Global Navigation Satellite System (GLONASS) considering satellite navigation system environment in Polar Regions. The orbital inclination of GLONASS is $64.8^{\circ}$, which is suitable in order to ensure satellite visibility in high-latitude regions. In contrast, GLONASS has different system operation elements such as configuration elements of navigation message and update cycle and has a statistically different signal error level around 4 m, which is larger than that of GPS. Thus, such system characteristics must be taken into consideration to ensure data integrity and monitor GLONASS signal fault. This study took GLONASS system characteristics and performance into consideration to improve previously developed fault detection algorithm in the local-area augmentation system based on GPS. In addition, real GNSS observation data were acquired from the receivers installed at the Antarctic King Sejong Station to analyze positioning accuracy and calculate test statistics of the fault monitors. Finally, this study analyzed the satellite visibility of GPS/GLONASS-based local-area augmentation system in Polar Regions and conducted performance evaluations through simulations.

• 한국항행학회논문지
• /
• 제22권6호
• /
• pp.610-615
• /
• 2018

세계적으로 GNSS (global navigation satellite system)는 선진국에서 개발 및 운용 중에 있다. 가장 대표적인 시스템인 GPS (global positioning system)을 시작으로 현재 중국의 Beidou가 빠르게 발전하고 있다. 본 논문에서는 빠르게 변화하는 Beidou의 활용을 위해 현재 시점의 한국지역에서 Beidou 위성의 가시성 분석을 수행한다. 이렇게 수행되는 분석에서 안정적으로 서비스되고 있는 GPS와 비교하며 진행하도록 한다. 가시성분석은 mask angle (저앙각 위성 배제 각도)에 따른 결과, skyplot (사용자 위치에서 위성의 위치를 가시적으로 표현하기 위한 그림)을 통한 결과를 수행하였다. 가시성 분석을 통해 한국지역에서 GPS위성에 비해 Beidou 위성의 고앙각 배치가 많아지는 것을 확인 할 수 있다. 또한 고앙각 배치가 많아지는 것의 효과를 확인하기 위해 GPS와 Beidou의 가용성 및 위치정확도 분석을 수행한다. 수행 결과에 따라 한국지역에서 고앙각 위성을 활용 할 시 GPS보다 Beidou가 더 효과적일 것으로 확인된다.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2012년도 춘계학술대회
• /
• pp.872-875
• /
• 2012

Recently, China officially declared to operate its satellite positioning system, Beidou so called Compass. The system is currently having 10 orbiting satellites which regionally cover from Australia to Russia in the north. Moreover, the system will be planed not only to launch 6 navigation satellites in its orbit in 2012 but also to complete the system with 35 satellites in 2020. The China satellite navigation system can affect to the current circumstance of global satellite navigation world in terms of navigation parameters. In this paper, we investigate characteristics of multi-integrated GNSS involving Beidu-Compass system and discuss general issues involving visibility and GDOP.

• Journal of Astronomy and Space Sciences
• /
• 제28권4호
• /
• pp.319-332
• /
• 2011

The objectives of this study are to analyze the satellite visibility at the randomly established ground sites, to determine the five optimal ground sites to perform the optical surveillance and tracking of domestic satellites, and to verify the acquisition of the optical observation time sufficient to maintain the precise ephemeris at optimal ground sites that have been already determined. In order to accomplish these objectives, we analyzed the visibility for sun-synchronous orbit satellites, low earth orbit satellites, middle earth orbit satellites and domestic satellites as well as the continuous visibility along with the fictitious satellite ground track, and calculate the effective visibility. For the analysis, we carried out a series of repetitive process using the satellite tool kit simulation software developed by Analytical Graphics Incorporated. The lighting states of the penumbra and direct sun were set as the key constraints of the optical observation. The minimum of the observation satellite elevation angle was set to be 20 degree, whereas the maximum of the sun elevation angle was set to be -10 degree which is within the range of the nautical twilight. To select the candidates for the optimal optical observation, the entire globe was divided into 84 sectors in a constant interval, the visibility characteristics of the individual sectors were analyzed, and 17 ground sites were arbitrarily selected and analyzed further. Finally, five optimal ground sites (Khurel Togoot Observatory, Assy-Turgen Observatory, Tubitak National Observatory, Bisdee Tier Optical Astronomy Observatory, and South Africa Astronomical Observatory) were determined. The total observation period was decided as one year. To examine the seasonal variation, the simulation was performed for the period of three days or less with respect to spring, summer, fall and winter. In conclusion, we decided the optimal ground sites to perform the optical surveillance and tracking of domestic satellites and verified that optical observation time sufficient to maintain the precise ephemeris could be acquired at the determined observatories.