• 대한공간정보학회지
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• 제13권1호
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• pp.63-69
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• 2005

InSAR(Interferometric Synthetic Aperture Radar)는 급속히 발진하고 있는 기술이며 지표면의 수치지형모델 제작과 토지이용 분류뿐만 아니라, 지진, 화신, 지반침하와 빙하흐름의 모니터링과 같은 다양한 응용분야 적용은 그것의 장점을 강화시켜 주고 있다. InSAR는 원격탐측 기술의 한 부류이므로, 위성위치와 자세, 대기, 그리고 기타 요소에 의한 다양한 오차원인을 가지고 있으므로, 이 시스템의 정확도 검증, 특별히 SAR 영상으로부터 제작된 수치지형모델에 대해서는 중요하다. 본 연구에서는 RTK GPS와 Kinematic GPS 측위가 InSAR 기술로 제작된 수치지형모델의검증 도구로 이용되었다. 그 결과로서, Kinematic GPS는 실험지역에서 RTK GPS보다 많은 관측값을 얻을 수 있었지만, 안테나 주위 나무 등에 의한 위성추적 문제와 통신거리에 따른 기준국과 이동국사이의 자료전송 문제 등이 여전히 시급히 해결해야 할 과제로 나타났다.

• Journal of Positioning, Navigation, and Timing
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• 제6권4호
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• pp.205-210
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• 2017

Multi-Global Navigation Satellite System (GNSS) can significantly improve the positioning accuracy and convergence speed. The reliability and availability of multi-GNSS precise point positioning (PPP) is steadily increasing with the rapid development of GNSS satellites. In this study, multi-GNSS PPP analysis is performed to compare the positioning precision by processing the observations from different GNSS systems (GPS, GLONASS, Galileo and BeiDou). To improve the positioning performance of the multi-GNSS PPP, we employed the weighed measurement noise (WMN) method. After applying WMN method to multi-GNSS PPP, positioning precision is improved by approximately 26.3% compared to the GPS only solutions, and by approximately 9.1% compared to combined GPS, GLONASS, and Galileo PPP.

• Journal of Positioning, Navigation, and Timing
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• 제8권2호
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• pp.87-94
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• 2019

The Global Navigation Satellite System (GNSS) Real-Time Kinematic (RTK) positioning has been widely used in geodesy, surveying, and navigation fields. RTK can benefit enormously from the integration of multi-GNSS. In this study, we develop a GPS/BeiDou Navigation Satellite System (BDS) RTK integration algorithm for long baselines ranging from 128 km to 335 km in South Korea. The positioning performance with GPS/BDS RTK, GPS-only RTK, and BDS-only RTK is compared in terms of the positioning accuracy. An improvement of positioning accuracy over long baselines can be found with GPS/BDS RTK compared with that of GPS-only RTK and that of BDS-only RTK. The positioning accuracy of GPS/BDS RTK is better than 2 cm in the horizontal direction and better than 5 cm in the vertical direction. A lower Relative Dilution of Precision (RDOP) value with GPS/BDS integration can obtain a better positional precision for long baseline RTK positioning.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.185-190
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• 2006

The correct estimation of the ionospheric delays is very important for the precise kinematic positioning especially in case of the long baseline. In case of triple frequency system, the ionospheric delays can be estimated from the measurements, but, in case of dual frequency system, the situation is not so simple. The precision of those supplied by the external information source such as IONEX is not sufficient. The high frequency component is neglected, and the precision of the low frequency component is not sufficient for the long baseline positioning. On the other hand, the high frequency component can be estimated from the phase range measurements. If the low frequency components are estimated by using the external information source or pseudo range measurements, a more reasonable estimation of the ionospheric delays may be possible. It has already been discussed by the author that the estimation of the low frequency components by using the external information source is not sufficient but fairly effective. The estimation using the pseudo range measurements is discussed in the present paper. The accuracy is not sufficient at present because of the errors in the pseudo range measurements. It is clarified that the bias errors in the pseudo range measurements are responsible for the poor accuracy of the ionospheric delays. However, if the accuracy of the pseudo range measurements is improved in future, the method would become very promising.

• Korean Journal of Geomatics
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• 제2권1호
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• pp.65-73
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• 2002

GPS in the United States and GLONASS of the old Soviet Union are used currently as satellite navigation systems. Plans are being made to use the Galileo satellite system in Europe, and these plans focus on a combined application of the satellite navigation systems. In this study, we examined the possibility of effective application of a combination of GPS/GLONASS in urban areas, where 3-dimensional positioning is impossible with GPS alone. We analyzed the 3-D coordinate deviation of a GLONASS satellite by integration interval and compared it with GLONASS satellite coordinates in precise ephmerides by transforming it into WGS84. We also programmed GPS/GLONASS, analyzed 3-D positioning accuracy by static surveying and kinematic surveying with Ashtech Z18 receivers and Legacy receivers, and then compared the results to those of GPS surveying. As a result, we are able to decide the integration interval for producing GLONASS satellite coordinates in navigation and geographical information and construct a GPS/GLONASS data processing system by developing a DGPS/DGLONASS positioning program. If more than four GLONASS satellites are observed, the accuracy of GPS/GLONASS is better than that of GPS positioning. As a result of kinematic surveying in a congested urban area with skyscrapers, we discovered that the GPS/LONASS combination is very effective.

• 한국측량학회지
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• 제26권5호
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• pp.493-504
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• 2008

SBAS(Space-Based Augmentation System)는 광역보정항법시스템(WADGPS, Wide Area DGPS)으로써 지역 보정항법시스템(LADGPS, Local Area DGPS)의 단점을 보완한 위성항법 보정시스템이다. 이 연구에서는 GPS 측위의 대표적인 방법인 실시간 이동측위(RTK; Real-Time Kinematic), DGPS(Differential GPS) 측위, 단독측위(Standalone)와 SBAS 이동측위를 실시하고 그에 따른 측위 정확도 비교를 통해 SBAS 이동측위의 성능을 분석하였다. 정지측위 결과 산출한 좌표를 참값으로 간주하였고, 각각의 측위방법으로 획득한 관측데이터를 참값과 비교하여 계산한 2차원 평균제곱근(RMS: Root Mean Square)오차와 3차원 RMS 오차를 정확도 비교의 지표로 사용하였다. 그 결과, 각 측위방법에 따른 3차원 RMS 오차는 RTK 측위 13.1cm, DGPS 측위 126.0cm, 이중주파수 단독측위 135.7cm, 단일주파수 단독측위 428.9cm, 그리고 SBAS 측위 109.2cm로 나타났다. 이를 통해 SBAS 측위의 정확도가 DGPS 측위 정확도와 대등한 수준임을 확인할 수 있었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.429-429
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• 2000

Micro positioning mechanism is the key technology in many fields, such as scanning electron microscopy (SEM), x-ray lithography, mask alignment and micro-machining. In the paper, a 3DOF parallel-type micro-positioning mechanism is proposed. This mechanism uses piezo-actuators and Flexure hinge to control x, y and $\theta$ motion. It is shown both analytically and numerically that 2 DOF flexure hinge model was better precision than 1 DOF flexure hinge design.

• Journal of Positioning, Navigation, and Timing
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• 제6권4호
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• pp.211-221
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• 2017

Ellipsodially referenced survey (ERS) is considered as one of the challenging issues in the hydrographic surveys due to the fact that the bathymetric data collected by this technique can be readily transformed either to the geodetic or the chart datum by application of some geoscientific models. Global Navigation Satellite Systems (GNSS) is a preferred technique to determine the ellipsoidal height of a vessel reference point (RP) because it provides cost-effective and unprecedentedly accurate positioning solutions. Especially, the GNSS-derived heights include heave and dynamic draft of a vessel, so as for the reduced bathymetric solutions to be potentially free from these corrections. Although over the last few decades, differential GNSS (DGNSS) has been widely adopted in the bathymetric surveys, it only provides limited accuracy of the vertical component. This technical barrier can be effectively overcome by adopting the so-called GNSS carrier phase (CPH) based techniques, enhancing accuracy of the height solution up to few centimeters. From the positioning algorithm standpoint, the CPH-based techniques are categorized under absolute and relative positioning in post-processing mode; the former is precise point positioning (PPP) correcting errors by the global or regional models, the latter is post-processed kinematic positioning (PPK) that uses the differencing technique to common error sources between two receivers. This study has focused on assessment of achievable accuracy of the ellipsoidal heights obtained from these CPH-based techniques with a view to their applications to hydrographic surveys where project area is, especially, few tens to hundreds kilometers away from the shore. Some field trials have been designed and performed so as to collect GNSS observables on static and kinematic mode. In this paper, details of these tests and processed results are presented and discussed.

• Journal of Positioning, Navigation, and Timing
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• 제6권1호
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• pp.35-41
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• 2017

Precise Point Positioning (PPP) method is based on dual-frequency data of Global Navigation Satellite Systems (GNSS). The recent multi-constellations GNSS (multi-GNSS) enable us to bring great opportunities for enhanced precise positioning, navigation, and timing. In the paper, the multi-GNSS PPP with a combination of four systems (GPS, GLONASS, Galileo, and BeiDou) is analyzed to evaluate the improvement on positioning accuracy and convergence time. GNSS observations obtained from DAEJ reference station in South Korea are processed with both the multi-GNSS PPP and the GPS-only PPP. The performance of multi-GNSS PPP is not dramatically improved when compared to that of GPS only PPP. Its performance could be affected by the orbit errors of BeiDou geostationary satellites. However, multi-GNSS PPP can significantly improve the convergence speed of GPS-only PPP in terms of position accuracy.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2010년 춘계학술발표회 논문집
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• pp.169-171
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• 2010

The goal of this study is to evaluate the performance of different solution types(a GPS-only, a GLONASS-only, and a GNSS solution) on GNSS positioning modes which are point positioning and relative positioning(DGNSS-, Static-, and Kinematic-solutions). I started with GNSS sites of seoul metropolitan government's RTK network which providing combined GPS/GLONASS observations : Gangseo(GANS), Dobong(DBON). The positioning accuracy of different solution types on positining modes are compared. Considering the compared results of all cases, can find not only the difference of the performance between the GNSS solution and the GPS-only solution is very small, but also the GLONASS-only solution is not far from the other solution types taking into consideration that GLONASS system is not (yet) a complete system.