• Title, Summary, Keyword: ephemeris

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Development of Kinematic Ephemeris Generator for Korea Pathfinder Lunar Orbiter (KPLO)

  • Song, Min-Sup;Park, Sang-Young;Kim, Youngkwang;Yim, Jo Ryeong
    • Journal of Astronomy and Space Sciences
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    • v.37 no.3
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    • pp.199-208
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    • 2020
  • This paper presents a kinematic ephemeris generator for Korea Pathfinder Lunar Orbiter (KPLO) and its performance test results. The kinematic ephemeris generator consists of a ground ephemeris compressor and an onboard ephemeris calculator. The ground ephemeris compressor has to compress desired orbit propagation data by using an interpolation method in a ground system. The onboard ephemeris calculator can generate spacecraft ephemeris and the Sun/Moon ephemeris in onboard computer of the KPLO. Among many interpolation methods, polynomial interpolation with uniform node, Chebyshev interpolation, Hermite interpolation are tested for their performances. As a result of the test, it is shown that all the methods have some cases that meet requirements but there are some performance differences. It is also confirmed that, the Chebyshev interpolation shows better performance than other methods for spacecraft ephemeris generation, and the polynomial interpolation with uniform nodes yields good performance for the Sun/Moon ephemeris generation. Based on these results, a Kinematic ephemeris generator is developed for the KPLO mission. Then, the developed ephemeris generator can find an approximating function using interpolation method considering the size and accuracy of the data to be transmitted.

Accuracy Analysis of baseline determination using Broadcast ephemeris and Precise ephemeris in GPS surveying (방송력과 정밀력의 사용에 의한 GPS 측량의 정확도 분석)

  • Kim, Cheol-Young;Lee, Suk-Bae;Do, Sang-Gyeong
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.27 no.2
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    • pp.149-157
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    • 2009
  • The orbit ephemeris of Global Positioning System(GPS) is one element to determine the surveying accuracy and there are broadcasting ephemeris and precise ephemeris, IGS rapid orbit and IGS ultra rapid orbit in the orbit ephemeris of GPS. In this study, test area was selected in Uljin, Kyungsanbukdo and GPS surveying was accomplished at 37 points in the test area. Then baseline solution was done on 74 baseline using broadcasting ephemeris and precise ephemeris and analysis by TGO and the results were compared. Comparison results were showed that there were nearly no difference between the two results but in case of relative precision of the baseline, it was slightly better the baseline results of precise ephemeris which showed 0.706ppm than the baseline results of broadcasting ephemeris which showed 0.708ppm.

Validation of Geostationary Earth Orbit Satellite Ephemeris Generated from Satellite Laser Ranging

  • Oh, Hyungjik;Park, Eunseo;Lim, Hyung-Chul;Lee, Sang-Ryool;Choi, Jae-Dong;Park, Chandeok
    • Journal of Astronomy and Space Sciences
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    • v.35 no.4
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    • pp.227-233
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    • 2018
  • This study presents the generation and accuracy assessment of predicted orbital ephemeris based on satellite laser ranging (SLR) for geostationary Earth orbit (GEO) satellites. Two GEO satellites are considered: GEO-Korea Multi-Purpose Satellite (KOMPSAT)-2B (GK-2B) for simulational validation and Compass-G1 for real-world quality assessment. SLR-based orbit determination (OD) is proactively performed to generate orbital ephemeris. The length and the gap of the predicted orbital ephemeris were set by considering the consolidated prediction format (CPF). The resultant predicted ephemeris of GK-2B is directly compared with a pre-specified true orbit to show 17.461 m and 23.978 m, in 3D root-mean-square (RMS) position error and maximum position error for one day, respectively. The predicted ephemeris of Compass-G1 is overlapped with the Global Navigation Satellite System (GNSS) final orbit from the GeoForschungsZentrum (GFZ) analysis center (AC) to yield 36.760 m in 3D RMS position differences. It is also compared with the CPF orbit from the International Laser Ranging Service (ILRS) to present 109.888 m in 3D RMS position differences. These results imply that SLR-based orbital ephemeris can be an alternative candidate for improving the accuracy of commonly used radar-based orbital ephemeris for GEO satellites.

A study on the Precision Improvement of Baseline Determination by Using the Precise Ephemeris of GPS Satellites (GPS위성의 정밀궤도력에 의한 기선결정의 정밀도 향상에 관한 연구)

  • 박필호;박종욱;조정호
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.14 no.2
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    • pp.199-207
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    • 1996
  • According to the different baseline lengths, we quantitatively analyzed how much precision of the baseline de-termination is improved for GPS survey when using the precise ephemeris instead of the broadcast ephemeris of GPS satellites. For this research, we selected seven baselines ranging from 15 km to 201 km and performed GPS measurements more than six times for each baseline. The observed data for each baseline were processed two times with the same conditions alternately changing the broadcast and the precise ephemeris. The standard deviations from the repeated measurements for each baseline are compared between the results of using the broadcast ephemeris and the precise ephemeris. As the result, the precision, stability and reliability of the base-line determination using the precise ephemeris is better than those of using the broadcast ephemeris for all base-lines. When using precise ephemeris for the baselines longer than 65 km, the precision less than 0.1ppm is always obtained and the precision improvement rate by using the precise ephemeris is considerably greater than that for the shorter baselines. We expect that this result might be a quantative basis for the decision about what ephemeris is better for the baseline length and the demanded precision in GPS survey.

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Evaluation of Geometric Modeling for KOMPSAT-1 EOC Imagery Using Ephemeris Data

  • Sohn, Hong-Gyoo;Yoo, Hwan-Hee;Kim, Seong-Sam
    • ETRI Journal
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    • v.26 no.3
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    • pp.218-228
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    • 2004
  • Using stereo images with ephemeris data from the Korea Multi-Purpose Satellite-1 electro-optical camera (KOMPSAT-1 EOC), we performed geometric modeling for three-dimensional (3-D) positioning and evaluated its accuracy. In the geometric modeling procedures, we used ephemeris data included in the image header file to calculate the orbital parameters, sensor attitudes, and satellite position. An inconsistency between the time information of the ephemeris data and that of the center of the image frame was found, which caused a significant offset in satellite position. This time inconsistency was successfully adjusted. We modeled the actual satellite positions of the left and right images using only two ground control points and then achieved 3-D positioning using the KOMPSAT-1 EOC stereo images. The results show that the positioning accuracy was about 12-17 m root mean square error (RMSE) when 6.6 m resolution EOC stereo images were used along with the ephemeris data and only two ground control points (GCPs). If more accurate ephemeris data are provided in the near future, then a more accurate 3-D positioning will also be realized using only the EOC stereo images with ephemeris data and without the need for any GCPs.

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Orbit Ephemeris Failure Detection in a GNSS Regional Application

  • Ahn, Jongsun;Lee, Young Jae;Won, Dae Hee;Jun, Hyang-Sig;Yeom, Chanhong;Sung, Sangkyung;Lee, Jeong-Oog
    • International Journal of Aeronautical and Space Sciences
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    • v.16 no.1
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    • pp.89-101
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    • 2015
  • To satisfy civil aviation requirements using the Global Navigation Satellite System (GNSS), it is important to guarantee system integrity. In this work, we propose a fault detection algorithm for GNSS ephemeris anomalies. The basic principle concerns baseline length estimation with GNSS measurements (pseudorange, broadcasted ephemerides). The estimated baseline length is subtracted from the true baseline length, computed using the exact surveyed ground antenna positions. If this subtracted value differs by more than a given threshold, this indicates that an ephemeris anomaly has been detected. This algorithm is suitable for detecting Type A ephemeris failure, and more advantageous for use with multiple stations with various long baseline vectors. The principles of the algorithm, sensitivity analysis, minimum detectable error (MDE), and protection level derivation are described and we verify the sensitivity analysis and algorithm availability based on real GPS data in Korea. Consequently, this algorithm is appropriate for GNSS regional implementation.

Analysis of Reliability for the GPS Surveying Data by Different Ephemeris (GPS관측자료의 궤도력 별 신뢰성 분석)

  • Jung, Young-Dong;Kang, Sang-Gu;Park, Bo-Yeon
    • Journal of Korean Society for Geospatial Information Science
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    • v.10 no.2
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    • pp.57-66
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    • 2002
  • This paper establised GPS network consist of 75km average baseline lengths over Jeollanamdo and Jeollabukdo nine point station and fixed Gwangju point station. We quantitavely analyzed how much precision of the baseline determination is improved for GPS survey when using the precise eqhemeris instead of tile broadcast ephemeris of GPS satellites. The observed data for each baseline were processed two times with the same conditions alternately changing the broadcast and the precise ephemeris. The standard deviations from the repeated measurments for each baseline ara compared between the results of using the broadcast ephemeris and the precise ephemeris. As the results, the precision, stability and reliability of the baseline determination using the precise ephemeris is better than those of using the broadcast ephemeris for all baselines.

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Accuracy Evaluation of IGS-RTS Corrections to Stand-Alone Positioning Based on GPS Code-Pseudorange Measurements

  • Kang, Min-Wook;Won, Jihye;Kim, Mi-So;Park, Kwan-Dong
    • Journal of Positioning, Navigation, and Timing
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    • v.5 no.2
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    • pp.59-66
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    • 2016
  • The International GNSS Service (IGS) provides the IGS-Real Time Service (IGS-RTS) corrections that can be used in stand-alone positioning in real time. In this study, the positioning accuracy before and after the application of the corrections to broadcast ephemeris by applying the IGS-RTS corrections at code pseudo-range based stand-alone positioning was compared with positioning result using precise ephemeris. The analysis result on IGS-RTS corrections showed that orbit error and clock error were 0.05 m and 0.5 ns compared to precise ephemeris and accuracy improved by about 8.5% compared to the broadcast ephemeris-applied result when the IGS-RTS was applied to positioning. Furthermore, regionally dispersed five observatories were selected to analyze the effect of external environments on positioning accuracy and positioning errors according to location and time were compared as well as the number of visible satellites and position dilution of precision by observatory were analyzed to verify a correlation with positioning error.

Performance Analysis of GNSS Ephemeris Fault Detection Algorithm Based on Carrier-Phase Measurement (반송파 측정값 기반 GNSS 궤도력 고장 검출 알고리즘 성능 분석)

  • Ahn, Jongsun;Jun, Hyang-Sig;Nam, Gi-Wook;Yeom, Chan-Hong;Lee, Young Jae;Sung, Sangkyung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.42 no.6
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    • pp.453-460
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    • 2014
  • We analyze fault detection algorithm of ephemeris included in navigation message, which is one of the GNSS risk factors. This algorithm uses carrier-phase measurement and baseline vector of two reference stations and is alternative method for uncertainty condition of previous ephemeris. Even though same ephemeris fault is occurred, the geometry condition, between baseline vector of reference stations and satellites, effects on performance of algorithm. Also, we introduce the suitable geometry of reference stations, threshold and performance index (MDE : Minimum Detectable Error) in jeju international airport.