• Journal of Positioning, Navigation, and Timing
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• v.11 no.4
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• pp.251-261
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• 2022

The Centimeter Level Augmentation Service (CLAS) is the Precise Point Positioning (PPP) - Real Time Kinematic (RTK) correction service utilizing the Quasi-Zenith Satellite System (QZSS) L6 (1278.65 MHz) signal to broadcast the Global Navigation Satellite System (GNSS) error corrections. Compact State-Space Representation (CSSR) corrections for mitigating GNSS measurement error sources such as satellite orbit, clock, code and phase biases, tropospheric error, ionospheric error are estimated from the ground segment of QZSS CLAS using the code and carrier-phase measurements collected in the Japan's GNSS Earth Observation Network (GEONET). Since the CLAS service begun on November 1, 2018, users with dedicated receivers can perform cm-level precise positioning using CSSR corrections. In this paper, CLAS-based VRS-RTK performance evaluation was performed using Global Positioning System (GPS) observables collected from the refence station, TSK2, located in Japan. As a result of performing GPS-only RTK positioning using the open-source software CLASLIB and RTKLIB, it took about 15 minutes to resolve the carrier-phase ambiguities, and the RTK fix rate was only about 41%. Also, the Root Mean Squares (RMS) values of position errors (fixed only) are about 4cm horizontally and 7 cm vertically.

• Journal of Astronomy and Space Sciences
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• v.25 no.4
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• pp.445-458
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• 2008

Image chain analysis of synthetic aperture radar (SAR) satellite is one of the primary activities for satellite design because SAR image quality depends on spacecraft bus performance as well as SAR payload. Especially, satellite pointing and stability error make worst effect on the original SAR image quality which is implemented by SAR payload design. In this research, Image chain analysis S/W was developed in order to analyze the SAR image quality degradation due to satellite pointing and stability error. This S/W consists of orbit model, attitude control model, SAR payload model, clutter model, and SAR processor. SAR raw data, which includes total 25 point targets in the scene of $5km{\times}5km$ swath width, was generated and then processed for analysis. High resolution mode (spotlight), of which resolution is 1m, was applied. The results of image chain analysis show that radiometric accuracy is the most degraded due to the pointing error. Therefore, the successful design of attitude control subsystem in spacecraft bus for enhancing the pointing accuracy is most important for image quality.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.27.5-28
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• 2010

The unexpected observation condition or insufficient measurement modeling can lead to uncertain measurement errors. The uncertain measurement error of orbit determination problem typically consists of noise, bias and drift. It must be removed by using a proper estimation process for better orbit accuracy. The estimation of noise and drift is not easy because of their random or unpredictable variation. On the other hand, bias is a constant difference between the mean of the measured values and the true value, so it can be simply removed. In this study, precision orbit determination with SLR observations considering range bias estimation is presented. The Yonsei Laser-ranging Precision Orbit Determination System (YLPODS) and SLR NP (Normal Point) observations of CHAMP satellite are used for this work. The SLR residual test is performed to estimate the range bias of each arc. The result shows that we can get better orbit accuracy through range bias estimation.

• Korean Journal of Remote Sensing
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• v.14 no.2
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• pp.137-148
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• 1998

An algorithm developed for the precision correction of high resolution satellite images is introduced in this paper. In general, the polynomial warping algorithm which derives polynomial equations between GCPs extracted from an image and a base map requires many GCPs well-distributed over the image. The precision correction algorithm described in this paper is based on a sensor-orbit-Earth geometry, and therefore, it is capable of correcting a raw image using only 2-3 GCPs. This algorithm estimates the errors on the orbit determination and the attitude of the satellite by using a Kalman filter. This algorithm was implemented, tested and integrated into the KITSAT-3 image preprocessing software.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.3
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• pp.221-235
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• 2024

Errors included in Global Navigation Satellite System (GNSS) measurements degrade the performance of user position estimation but can be mitigated by spatial correlation properties. Augmentation systems providing correction data can be broadly categorized into State Space Representation (SSR) and Observation Space Representation (OSR) methods. The satellite-based cm-level augmentation service based on the SSR broadcasts correction data via satellite signals, unlike the traditional Real-Time Kinematic (RTK) and Network RTK methods, which use OSR. To provide a large amount of correction data via the limited bandwidth of the satellite communication, efficient message structure design considering service area, correction generation, and broadcast intervals is necessary. For systematic message design, it is necessary to analyze the influence of error components included in GNSS measurements. In this study, errors in satellite orbits, satellite clocks for GPS, Galileo, BeiDou, and QZSS satellite constellations ionospheric and tropospheric delays over one year were analyzed, and their spatial decorrelations and linear modeling characteristics were examined.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.9
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• pp.64-74
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• 2003

This paper proposes a new autonomous stationkeeping system suitable for geostationary satellite and conducts computer simulation to verify the proposed algorithm. The proposed onboard system receives pseudo-range signal from ground equipments located at two different position with long baseline, determines the orbit error in realtime and generates orbit control commands. For minimized onboard stationkeeping logic and better reliability, the orbit controller is designed to generate control signal to have the orbit roughly follow predetermined reference range data which is generated through ground based computer simulation. The reference range data is assumed to be uploaded with time tag. A simple orbit controller is proposed which combines the reference $\Delta$V and feedback control signal. Finally, the performance of the proposed system is verified through the computer simulations.

• Journal of Astronomy and Space Sciences
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• v.19 no.2
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• pp.163-172
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• 2002

This article investigates the problem of data preprocessing for the precision orbit determination (POD) of low earth orbit satellite using GPS .aw data. Several data preprocessing algorithms have been developed to edit the GPS data automatically such that outlier deletion, cycle slip identification and correction, and time tag error correction. The GPS data are precisely edited for the accuracy of POD. Some methods of data preprocessing are restricted to the rate of the collections of the pseudorange and carrier phase measurements. This study considers the preprocessing efficiency varied with the rate, the quality of receiver and the altitude of the satellite's orbit. We also propose the proper methods in accordance with the rate for single frequency and dual frequency receivers.

• Aerospace Engineering and Technology
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• v.9 no.2
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• pp.36-43
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• 2010

A GEO satellite launched by Arian 5 ECA launcher will be located in a transfer orbit where it requires several Apogee burn maneuvers to reach the target orbit. To obtain the required performance of Apogee burn maneuvers, a calibration of gyro drift error needs to be performed before each maneuver. In this paper, a unique gyro calibration scheme which is applied to COMS is described and the calibration error budget analysis is performed.

• Proceedings of the KSRS Conference
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• v.1
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• pp.278-281
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• 2006

Korea Meteorological Administration(KMA) has issued the tropical storm(typhoon) warning or advisories when it was developed to tropical storm from tropical depression and a typhoon is expected to influence the Korean peninsula and adjacent seas. Typhoon information includes current typhoon position and intensity. KMA has used the Dvorak Technique to analyze the center of typhoon and it's intensity by using available geostationary satellites' images such as GMS, GOES-9 and MTSAT-1R since 2001. The Dvorak technique is so subjective that the analysis results could be variable according to analysts. To reduce the subjective errors, QuikSCAT seawind data have been used with various analysis data including sea surface temperature from geostationary meteorological satellites, polar orbit satellites, and other observation data. On the other hand, there is an advantage of using the Subjective Dvorak Technique(SDT). SDT can get information about intensity and center of typhoon by using only infrared images of geostationary meteorology satellites. However, there has been a limitation to use the SDT on operational purpose because of lack of observation and information from polar orbit satellites such as SSM/I. Therefore, KMA has established Advanced Objective Dvorak Technique(AODT) system developed by UW/CIMSS(University of Wisconsin-Madison/Cooperative Institude for Meteorological Satellite Studies) to improve current typhoon analysis technique, and the performance has been tested since 2005. We have developed statistical relationships to correct AODT CI numbers according to the SDT CI numbers that have been presumed as truths of typhoons occurred in northwestern pacific ocean by using linear, nonlinear regressions, and neural network principal component analysis. In conclusion, the neural network nonlinear principal component analysis has fitted best to the SDT, and shown Root Mean Square Error(RMSE) 0.42 and coefficient of determination($R^2$) 0.91 by using MTSAT-1R satellite images of 2005. KMA has operated typhoon intensity analysis using SDT and AODT since 2006 and keep trying to correct CI numbers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9A
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• pp.1313-1321
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• 2000

In recent years LEO(Low Earth Orbit) satellite communication systems have gained a lot of interest as high speed multimedia services by satellite are about to be provided. It is mandatory to use very efficient ECC(Error Correcting Code) to support high speed multimedia services over LEO satellite channel. Turbo codes developed by Berrou et al. in 1993 have been actively researched since it can achieve a performance close to the Shannon limit. In this paper, a LEO satellite channel model is adopted and the fading characteristics of LEO satellite channel are analyzed for the change of elevation angle in various propagation environments. The performance of turbo code is analyzed and compared to that of conventional convolutional code using the satellite channel model. In the simulation results using the Globalstar orbit constellations, performance of turbo codes shows 1.0~2.0dB coding gain compared to that of convolutional codes over all elevation angle and propagation environment ranges we have investigated. The performance difference resulting from the change of elevation angle in various propagation environments and the performance of different ECC are analyzed in detail, so that the results can be applied to choose an appropriate ECC scheme for various system environment.