• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.104-108
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• 2004

The most of the CDMA mobile communication depends on the GPS for the time synchronization. Then, we must prepare alternative system against the unusable GPS like a unexpectable accident or strategic purpose by the USA government. In this study, we have constructed ground test segment for the time synchronization system using the geostationary satellite. In addition. we have designed, manufactured and tested the transmitting and receiving board to receive 1 PPS signal from atomic clock for transmitting stored data in buffer to satellite modem and to produce 1 PPS signal from satellite modem for measuring time delay.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.5
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• pp.375-384
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• 2013

Most of regions within the city of Mokpo, located on the southwest coast of the Korean Peninsula, are subjected to significant subsidence because about 70% of the city is land reclaimed from the sea (Kim et al., 2005). In this study, we aimed to estimate the rate of subsidence over Mokpo by using PALSAR L-band dataset from 2006 to 2010. Time series analysis was performed as well using GPS surveying data from 2010 to 2012. Results from these two independent datasets are then compared and analyzed over the common period of time. GPS data processing provides the results of seasonal variation on the surface, that is, via repeatedly rising and falling in association with the periodic cycle. Therefore, a time series analysis was performed to calculate the rate of ground subsidence. The deformation rates calculated for the same point are 3.89cm/yr and 2.65cm/yr from the GPS data and SAR data, respectively. SAR and GPS data processing results show a very similar pattern in terms of magnitude of annual subsidence. Thus, if the two datasets are integrated together, new modeling on ground subsidence is feasible. Lastly, subsidence was detected in a landfill area in the city of Mokpo, which has been continuously occurring through 2012.

• Journal of Astronomy and Space Sciences
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• v.26 no.2
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• pp.229-236
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• 2009

KOorea Multi-purpose SATellite(KOMPSAT)-5 will be launched at 550km altitude in 2010. Accurate satellite position(20 cm) and velocity(0.03 cm/s) are required to treat highly precise Synthetic Aperture Radar(SAR) image processing. Ionosphere delay was eliminated using dual frequency GPS data and double differenced GPS measurement removed common clock errors of both GPS satellites and receiver. SAC-C carrier phase data with 0.1 Hz sampling rate was used to achieve precise orbit determination(POD) with ETRI GNSS Precise Orbit Determination(EGPOD) software, which was developed by ETRI. Dynamic model approach was used and satellite's position, velocity, and the coefficients of solar radiation pressure and drag were adjusted once per arc using Batch Least Square Estimator(BLSE) filter. Empirical accelerations for sinusoidal radial, along-track, and cross track terms were also estimated once per revolution for unmodeled dynamics. Additionally piece-wise constant acceleration for cross-track direction was estimated once per arc. The performance of POD was validated by comparing with JPL's Precise Orbit Ephemeris(POE).

• Journal of Korean Society for Geospatial Information Science
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• v.22 no.1
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• pp.47-54
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• 2014

Precise Point Positioning (PPP) algorithms using GPS code pseudo-range measurements were developed and their accuracy was validated for the purpose of implementing them on a portable device. The group delay, relativistic effect, and satellite-antenna phase center offset models were applied as fundamental corrections for PPP. GPS satellite orbit and clock offsets were taken from the International GNSS Service official products which were interpolated using the best available algorithms. Tropospheric and ionospheric delays were obtained by applying mapping functions to the outputs from scientific GPS data processing software and Global Ionosphere Maps, respectively. When the developed algorithms were tested for four days of data, the horizontal and vertical positioning accuracies were 0.8-1.6 and 1.6-2.2 meters, respectively. This level of performance is comparable to that of Differential GPS, and further improvements and fine-tuning of this suite of PPP algorithms and its implementation at a portable device should be utilized in a variety of surveying and Location-Based Service applications.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.6
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• pp.521-531
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• 2020

QZSS (Quasi-Zenith Satellite System) provides the CLAS (Centimeter Level Augmentation Service) through the satellite's L6 band. CLAS provides correction messages called C-SSR (Compact - State Space Representation) for GPS (Global Positioning System), Galileo and QZSS. In this study, CLAS messages were received by using the AsteRx4 of Septentrio which is a GPS receiver capable of receiving L6 bands, and the messages were decoded to acquire C-SSR. In addition, Multi-GNSS (Global Navigation Satellite System) Code-PPP (Precise Point Positioning) was developed to compensate for GNSS errors by using C-SSR to pseudo-range measurements of GPS, Galileo and QZSS. And non-linear least squares estimation was used to estimate the three-dimensional position of the receiver and the receiver time errors of the GNSS constellations. To evaluate the accuracy of the algorithms developed, static positioning was performed on TSK2 (Tsukuba), one of the IGS (International GNSS Service) sites, and kinematic positioning was performed while driving around the Ina River in Kawanishi. As a result, for the static positioning, the mean RMSE (Root Mean Square Error) for all data sets was 0.35 m in the horizontal direction ad 0.57 m in the vertical direction. And for the kinematic positioning, the accuracy was approximately 0.82 m in horizontal direction and 3.56 m in vertical direction compared o the RTK-FIX values of VRS.

• Journal of Satellite, Information and Communications
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• v.2 no.1
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• pp.48-55
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• 2007

The system requirement definition, system configuration, major parameters for GNSS ground station development are presented in this paper. GNSS ground station system consists of the GNSS sensor station, up link station and monitoring & control system. The GNSS sensor station consists of navigation receiver subsystem which process the GPS and Galileo navigation signal, automic clock subsystem, meteorological data receiving subsystem and navigation data processing subsystem. To communicate the error correction of navigation fate, GNSS sensor station interface with GNSS Control Center.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.1
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• pp.9-18
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• 2006

This paper describes a new program called GPS_QC needed to check the quality of GPS observations before post-processing so that the surveyors can be improved the precision of GPS data analysis. The GPS_QC was designed to calculate the quality control (QC) parameters such as data gaps, cycle slips, low elevation angle, inonspheric delay, multi-path effects and DOP etc, within the period of GPS observation. It can be used to read and calculate the QC parameters from RINEX files. This program gives users brief statistics, time series plots and graphs of QC parameters. The GPS_QC can simply be performed the quality checking of GPS data that was difficult for surveyors in the field. It is expected that we can be improved the precision of positioning and solved the time consuming problem of GPS observation.

• Journal of the Korean Professional Engineers Association
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• v.37 no.2
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• pp.47-53
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• 2004

Space-based radio-positioning and time transfer system, Provide accurate position, velocity, and time(PVT) information \longleftarrowunlimited number of suitably equipped ground, sea, air and space users, by the U.S Department of Defense(DoD), Comprises major system segments\longrightarrowSpace, Control and User

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.21 no.1
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• pp.9-17
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• 2003

Typhoon RUSA, which caused serious damage was passed over in Korea peninsula during 30 August to 1 September, 2002. We estimated tropospheric wet delay using GPS data and meteorological data during this period. Integrated Water Vapor(IWV) gives the total amount of water vapor from tropospheric wet delay and Precipitable Water Vapor(PWV) is calculated the IWV scaled by the density of water. We obtained GPS PWV at 13th GPS permanent stations(Seoul, Wonju. Seosan, Sangju, Junju, Cheongju, Taegu, Wuljin, Jinju, Daejeon, Mokpo, Sokcho, Jeju). We retrieve GPS data hourly and use Gipsy-Oasis II software and we compare PWV and precipitation. GPS observed PWV time series demonstrate that PWV is, in general, high before and during the occurrence of the typhoon RUSA, and low after the typhoon RUSA. GPS PWV peak time at each station is related to the progress of a typhoon RUSA. We got very near result as we compare GMS Satellite image with tomograph using GPS PWV and we could present practical use possibility by numerical model for weather forecast.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.22 no.1
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• pp.37-44
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• 2004

This study aims to develop an optimized system for container management in Customs Free Zone. Positioning methods and wireless data communication methods were analyzed and then introduced to the container management system constructed in this study. For the trial test, it was founded that the accuracy of the GPS receiver using a single frequency band was not satisfied. However, the position of container can be matched with a digital map by map matching process. It was also founded that the precise method like Inverted DGPS is required when sight of a satellite is blocked.