• Journal of Astronomy and Space Sciences
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• v.29 no.3
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• pp.275-285
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• 2012

In this study, we present preliminary results of precise orbit determination (POD) using satellite laser ranging (SLR) observations for International Laser Ranging Service (ILRS) Associate Analysis Center (AAC). Using SLR normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2, the NASA/GSFC GEODYN II software are utilized for POD. Weekly-based orbit determination strategy is applied to process SLR observations and the post-fit residuals check, and external orbit comparison are performed for orbit accuracy assessment. The root mean square (RMS) value of differences between observations and computations after final iteration of estimation process is used for post-fit residuals check. The result of ILRS consolidated prediction format (CPF) is used for external orbit comparison. Additionally, we performed the precision analysis of each ILRS station by post-fit residuals. The post-fit residuals results show that the precisions of the orbits of LAGEOS-1 and LAGEOS-2 are 0.9 and 1.3 cm, and those of ETALON-1 and ETALON-2 are 2.5 and 1.9 cm, respectively. The orbit assessment results by ILRS CPF show that the radial accuracies of LAGEOS-1 and LAGEOS-2 are 4.0 cm and 5.3 cm, and the radial accuracies of ETALON-1 and ETALON-2 are 30.7 cm and 7.2 cm. These results of station precision analysis confirm that the result of this study is reasonable to have implications as preliminary results for administrating ILRS AAC.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2010.04a
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• pp.43-44
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• 2010

We present the analysis of space geodetic technique observation, Satellite Laser Ranging (SLR), to LAGEOS1 and LAGEOS2 for the definition of the Terrestrial Reference Frame (TRF). The data were analyzed in 7day arcs during about 9 years (2000/01/10 ~ 2008/12/29) using NASA Goddard's GEODYN/SOLVE II software. The comparison of the coordinates between ITRF2005 and TRF solutions determined in this work shows that there is no significant bias.

• Journal of Astronomy and Space Sciences
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• v.10 no.2
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• pp.189-196
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• 1993

Satellite laser ranging observation of LAGEOS II has been performed using the SLR System at Sheshan Laser Ranging Station, Shanghai Observatory. And we obtained 1,838 observational points. The observed range data is corrected by means of system delay correction using ground target observation, atmospheric refraction delay correction, offset correction, general relativistic correction and tide correction including solid tide, polar tide and ocean tide. As a result, the determined range delay mean value is 19.12m and the mean internal accuracy by means of polynomial fitting and least square method is $\pm$7cm. Corrected observational points are 1,340 and noise ratio to total observational points is 27.1%.

• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.269-277
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• 2013

In this study, we present results of precise orbital geodetic parameter estimation using satellite laser ranging (SLR) observations for the International Laser Ranging Service (ILRS) associate analysis center (AAC). Using normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2 in SLR consolidated laser ranging data format, the NASA/GSFC GEODYN II and SOLVE software programs were utilized for precise orbit determination (POD) and finding solutions of a terrestrial reference frame (TRF) and Earth orientation parameters (EOPs). For POD, a weekly-based orbit determination strategy was employed to process SLR observations taken from 20 weeks in 2013. For solutions of TRF and EOPs, loosely constrained scheme was used to integrate POD results of four geodetic SLR satellites. The coordinates of 11 ILRS core sites were determined and daily polar motion and polar motion rates were estimated. The root mean square (RMS) value of post-fit residuals was used for orbit quality assessment, and both the stability of TRF and the precision of EOPs by external comparison were analyzed for verification of our solutions. Results of post-fit residuals show that the RMS of the orbits of LAGEOS-1 and LAGEOS-2 are 1.20 and 1.12 cm, and those of ETALON-1 and ETALON-2 are 1.02 and 1.11 cm, respectively. The stability analysis of TRF shows that the mean value of 3D stability of the coordinates of 11 ILRS core sites is 7.0 mm. An external comparison, with respect to International Earth rotation and Reference systems Service (IERS) 08 C04 results, shows that standard deviations of polar motion $X_P$ and $Y_P$ are 0.754 milliarcseconds (mas) and 0.576 mas, respectively. Our results of precise orbital and geodetic parameter estimation are reasonable and help advance research at ILRS AAC.

• Bulletin of the Korean Space Science Society
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• 2005.04a
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• pp.50-50
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• 2005

• Bulletin of the Korean Space Science Society
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• 1993.04a
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• pp.7.1-7
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• 1993

위성의 정밀 거리 결정을 위해 1993년 9월 5일부터 IS일간 중국의 상해 천문대 Sheshan관측소와 장춘 인공위성 관측소에서 LAGEOS 11 (Laser Geodynamics Satellite II)에 대한 SLR (Satellite Laser Ranging) 관측을 수행하였다. SLR 관측에서는 지상의 관측소에서 발사한 LASER 펄스 (pulse)가 반사경들(retroflectors)로 둘러싸인 인공위성에 반사되어 돌아오는 RTT (Round Trip Time)를 측정하여 위성까지의 거리를 결정하는데, 관측된 시간과 거리 자료는 많은 잡음(noise)를 포함하고 있기 때문에 정확한 자료를 얻기 위해서는 많은 보정이 필요하다. 관측된 시간, 거리 자료를 지상 목표물 조준(ground target ranging )에 의한 system보정, 원자시계와 GPS에서 수신된 시간과의 시간 비교, 측정된 온도, 기압, 상대 습도에 따른 대기 영향의 보정 등을 통해 오차를 줄이고 다시 LASERF beam의 대기 굴절에 따른 거리 변화 보정, 위성의 질량 중심 거리(offset) 보정, 조석력에 의한 변화값 보정, 전자기적 지연(electromagnetic delay)에 의한 상대론적 보정등을 통해서 정밀한 거리 자료를 얻었다.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.159.2-159.2
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• 2012

In this study, we propose an effective strategy for precise orbital and geodetic parameter estimation using SLR (Satellite Laser Ranging) observations for ILRS AAC (Associate Analysis Center). The NASA/GSFC GEODYN II software and SLR normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2 are utilized for precise orbital and geodetic parameter estimation. Weekly-based precise orbit determination strategy is applied to process SLR observations, and Precise Orbit Ephemeris (POE), TRF (Terrestrial Reference Frame), and EOPs (Earth Orientation Parameters) are obtained as products of ILRS AAC. For improved estimation results, selection strategies of dynamic and measurement models are experimently figured out and configurations of various estimation parameters are also carefully chosen. The results of orbit accuracy assessment of POE and precision analysis of TRF/EOPs for each case are compared with those of existing results. Finally, we find an appropriate strategy for precise orbital and geodetic parameter estimation using SLR observations for ILRS AAC.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2006.04a
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• pp.99-104
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• 2006

The new gravity field combination models are expected to improve the knowledge of the Earth's global gravity field. This study evaluates eleven global gravity field models derived from gravimetry and altimetry surface data in a comparison with ground truth in South Korea. Geoid heights obtained from GPS and levelling in South Korea are compared with geoid heights from the models. The results show that the gravity satellites CHAMP, GRACE and LAGEOS plus gravimetry and altimetry surface data have led to an improvement in gravity field models. As expected, the new combination gravity field model which are EIGEN-CG03C and EIGEN-GL04C give better results than the predecessors widely used models(EGM96, OSU91A etc.).