• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.18 no.4
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• pp.379-385
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• 2000

In order to evaluate the stability of permanent GPS arrays for obtaining high precision coordinates, spectral analysis uses the least square spectrum analysis to the coordinate variations of Suwon, Tsukuba and Sanghai stations. Permanent GPS observations at Suwon, Tsukuba and Sanghai have been more or less continuously carried out since 1994. Time series of the resulting coordinate variations are analyzed for long term repeatability and periodic behaviour.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.605-607
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• 2006

한국지질자원연구원은 1990년대 초반부터 순차적으로 강원도 경주, 양산, 삼척, 홍성, 정선, 지리산 등 6 개 지역에 GPS위성들이 발사하는 자료를 연속적으로 수신하여 자동관리할 수 있는 GPS 상시관측소를 설치하고 GPS위성자료를 축적해 왔다. 이에 한국지질자원연구원은 축적된 자료 중 2005년과 2006년에 걸친 자료를 이용하여 정밀좌표를 계산하였다. 자료처리에는 스위스 Bern대학이 개발한 Bernese4.0을 이용하였다. 이렇게 계산된 위 6 개 GPS상시관측소의 정밀 좌표를 이용함으로써 GPS위성자료를 사용하는 하는 지구과학 분야 및 측량 분야의 발전에 기여할 것이다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.22 no.2
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• pp.105-116
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• 2004

According to the developing advanced techniques and removal of Selective Availability, much research has been conducted to improve the accuracy of GPS positioning in absolute and relative mode by estimating the nuisance parameters such as atmospheric effect, clock errors and multipath. Especially, the continuous effort of establishing the CORS in many countries and the effort of ICS making effective global networking make more application areas and the necessity of more precise location is being increased. Some of the countries like German, Japan and Swiss already utilized the Virtual Reference System for better location accuracy and services. In this study, the VRS system is investigated in terms of system principle, required H/W and S/W, management and operation, revision of related law, expected application and market etc. and find optimal solution in each aspect for economic and fast set up of the system in this country. The analysis of Korean CORS, communication infra and market estimation is performed for the efficient system establishment. Also. the suggestion on the advertisement and education of the system is also included. It is expected that this study contributes for the establishment of effective and precise nationwide location service so that many SOC areas including navigation, GIS, Telematics, LBS can provides better service for the users.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.272-272
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• 2019

보는 수로나 하천의 수위를 조절하고 취수 등의 편의를 제공하기 위해 건설되는 하천 구조물이다. 일반적인 보(고정보)는 상시 담수 되어 농업용수, 생활용수, 공업용수 등의 취수원으로 활용되지만, 최근에 설치되는 보(가동보)들은 수문을 설치하여 필요에 따라 수위를 조절할 수 있게 되어 있다. 이와 같은 보의 운영은 보 상류의 유속, 수심, 흐름 특성, 하천 형상 등의 변화를 발생시킨다. 이에 따라 보 상류에 위치한 수위관측소의 수리학적 영향에 대하여 검토할 필요가 있다. 본 연구에서는 광주천 유역에 위치한 광주광역시(유촌교)관측소를 대상으로 하류 900m에 위치한 가동보 수문 운영 조건에 따른 보 상류부의 수위, 유속, 수심, 흐름 특성을 조사하고 가동보의 수문 개방과 폐쇄에 따른 영향을 분석하였다. 가동보는 상시 폐쇄되어 있으며, 강우 발생 시에만 일정 수위 이상에서 자동으로 개방되는 형태로 운영되고 있다. 본 연구에서는 총 30회의 수위관측 및 유량측정을 하였다. 가동보 운영에 따른 수위, 유속, 흐름 특성 변화와 유량 자료를 확보하기 위해 광주시청 및 광주환경공단의 협조 요청을 통해 광주광역시(유촌교)관측소를 기준으로 상류 약 50m와 하류 약 420m에 측정 위치를 선정하여 동시 유량측정을 하였다. 또한 가동보 운영에 따른 수면경사의 정도를 파악하기 위해 광주광역시(유촌교)관측소를 기준으로 상류 약 50m, 10m, 5m, 하류 약 420m, 500m, 900m에 각각 수위표를 설치하여 총 6회 수면경사를 계측하였다. 그 결과 광주광역시(유촌교)관측소에서는 보 수문 운영에 따라 수리학적 영향을 받는 것으로 분석되었고 이를 이용하여 흐름 특성 변화를 반영한 수위-유량관계곡선식을 개발하였다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.1
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• pp.13-20
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• 2010

Currently, GPS data process software appears different results that according to user's skills or software. Also, lots of time and efforts are necessary for using GPS data process software to general user, not a specialist On the other band, on-line GPS data process service have a merit that can cony out GPS data process without technical efforts and time. In this study, permanent GPS site's observation data of NGII(National Geographic Information Institute) was processed by on-line GPS data process service, and utilization assessment of on-line GPS data process service was performed by comparing this result with notified coordinates by the NGII in order to analyze positional accuracy. 10 permanent GPS sites of NGII including Suwon which is registered in IGS(International GNSS Service) were selected and these GPS observation data was processed by AUSPOS and CSRS-PPP.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.2
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• pp.13-20
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• 2010

Currently, NGII(National Geographic Information Institute) provides VRS(Virtual Reference System) service using 44 CORS(Continuously Operating Reference Stations). Since the VRS provides high-precision coordinate in a short time, the users and applications are expected to be rapidly increasing. The accuracy analysis on the VRS service, however, was not sufficiently performed yet. Therefore, in this study, the VRS data is acquired from various circumstances and its accuracy is analyzed. According to analysis, it was concluded that the VRS could be applied to public control point survey. Furthermore, it was found that the PQ(Position Quality) which represents variance of estimated coordinates rather than GDOP(Geometric Dilution of Precision) is more relevant as a factor to determine the accuracy of coordinates. Based on the analysis of data from four manufacturers (TRIMBLE, MAGELLAN, LECIA, TOPCON), it was confirmed that the standard deviations better than 3cm. Therefore, VRS Survey apply to public control point survey.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.4
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• pp.31-39
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• 2010

In this study, the performance of the online GPS processing services provided by diverse institutions was compared so that domestic GPS users in geodesy and surveying can easily get precise coordinates using those services. In order to evaluate the accuracy of each online GPS processing service, we calculated coordinates of seven GPS permanent stations located in Korea and foreign countries using APPS, CSRS-PPP, AUSPOS and OPUS. And the results were compared with published coordinates by IERS and National Geographic Information Institute. In the cases of foreign stations, the mean value of the horizontal errors was 9.3 mm and the descending order of accuracies was APPS, AUSPOS, OPUS and CSRS-PPP. In the cases of Korean stations, the mean value of the horizontal errors was 37.6 mm, although the order of accuracy was similar to the foreign cases; AUSPOS, APPS, OPUS and CSRS-PPP. Also, the average value of 3-D errors in Korean cases was about 3 cm larger than that of foreign cases and a bias of 3 cm was observed in the north direction.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.6
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• pp.621-628
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• 2018

More than four visible GPS (Global Positioning System) satellites are required to obtain absolute positioning. However, it is not easy to satisfy this condition when a rover is in such unfavorable condition as an urban area. As a consequence, clock-aided positioning has been used as an alternative method especially when the number of visible satellites is three providing that receive clock error information is available. In this study, LSC (Least-Squares Collocation) method is proposed to interpolate clock errors for clock-aided positioning after analyzing the characteristics of receiver clock errors. Numerical tests are performed by using GPS data collected at one of Korean CORS (Continuously Operating Reference Station) and a nearby GPS station. The receiver clock errors are obtained through the DGPS (Differential GPS) positioning technique and segmentation procedures are applied for efficient interpolation. Then, LSC is applied to predicted clock error at epoch which clock information is not available. The numerical test results are analyzed by examining the differences between the original and interpolated clock errors. The mean and standard deviation of the residuals are 0.24m and 0.49m, respectively. Therefore, it can be concluded that sufficient accuracy can be obtained by using the proposed method in this study.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.3
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• pp.293-301
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• 2011

The ionospheric delay is the largest error source in GPS positioning after the SA effect has been turned off in May, 2000. In this study, we used 44 permanent GPS stations being operated by National Geographic Information Institute (NGII) to estimate Total Electron Content (TEC) based on pseudorange measurements phase-leveled by a linear combination with carrier phases. The Differential Code Bias (DCB) of GPS satellites and receivers was estimated and applied for an accurate estimation of the TEC. To validate our estimates of DCB, changes of TEC values after DCB application were investigated. As a result, the RMS error went down by about an order of magnitude; from 35~45 to 3~4 TECU. After the DCB correction, ionospheric TEC maps were produced at a spatial resolution of $1^{\circ}{\times}1^{\circ}$. To analyze the effect of the number of sites used for map generation on the accuracy of TEC values, we tried 10, 20, 30, and 44 stations and the RMS error was computed with the Global Ionosphere Map as the truth. While the RMS error was 5.3 TECU when 10 sites are used, the error reduced to 3.9 TECU for the case of 44 stations.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.30 no.5
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• pp.477-484
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• 2012

Recently, as earthquake is more frequently taking place around the world due to diastrophism, the importance of diastrophism and disaster detection is becoming more important. In this study, to analyze the interpretation of seismic displacement by the Japanese earthquake in March, 2011, and monitor the diastrophism of plates in Japan and surrounding Eurasia, Pacific, and Philippines before and after the earthquake, the observational data from IGS observatories in Japan and Asian regions were processed by precise point positioning. The displacement was biggest in MIZU, which was the closest to the epicenter, and the earthquake-affected region was in inverse proportion to the distance from the epicenter. The result of calculating the diastrophism speed before and after the earthquake, based on precise point positioning of IGS observatories located in the 4 plates around Japan, showed that the displacement speed changed and different plates showed different results. The comparison with the plate fate model allowed to analyze the change in diastrophism by earthquake, and to understand the characteristics of the displacement of the plates around Japan. Later, a continuous diastrophism monitoring based on GPS is needed for earthquake prediction and diastrophism research, and the data gained by continuous GPS-based monitoring of diastrophism will be fully used as basic data for relevant research and earthquake disaster management.