• 천문학논총
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• 제30권2호
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• pp.659-661
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• 2015

The Long Baseline Array is an array of radio telescopes using the technique of Very Long Baseline Interferometry to achieve milli-arcsecond-scale angular resolution. The core telescopes are located in Australia, with telescopes in New Zealand and South Africa also participating regularly. In this paper the capabilities of the Long Baseline Array are described, and examples of the science undertaken with the array are given.

• 한국측량학회지
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• 제18권2호
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• pp.121-127
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• 2000

단시간 관측으로 많은 3차원 지형정보를 획득할 수 있는 GPS 이동측량은 수 km 이하의 단기선에서 주로 활용되고 있으며, 장기선에 대한 위치결정은 비교적 오랜 시간이 요구되는 정지 측량에 의존하고 있어 단시간으로 장기선 위치결정을 할 수 있는 방법이 요구되고 있다. 본 연구는 장기선에 대한 GPS 이동측량의 적용가능성을 검토하기 위하여 수 십 km 이상의 기선에 대한 기선거리별, 궤도력별 그리고 관측시간대별로 GPS 이동측량의 기선해석 정확도를 정지측량 결과와 비교ㆍ분석하고자 한다. 연구결과, PDOP이 4이하로 매우 양호한 경우 기선길이 약 60 km이하에서 신속정밀궤도력을 이용하면 수 분의 GPS측량으로 3차원 지형정보 획득이 가능할 것으로 기대되며, IGS의 최종 정밀궤도력을 적용한 경우와 유사한 정확도 획득이 가능함을 알 수 있었다. 앞으로 장기선 GPS 이동측량에 대한 더욱 심도 있는 연구가 진행된다면 국토개발을 비롯한 각종 건설분야에 필요한 지형정보를 보다 효율적으로 획득할 수 있을 것으로 기대된다.

• Journal of Positioning, Navigation, and Timing
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• 제3권3호
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• pp.123-129
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• 2014

The real-time kinematic (RTK) is one of precise positioning methods using Global Positioning System (GPS) data. In the long baseline GPS RTK, the ionospheric and tropospheric delays are critical factors for the positioning accuracy. In this paper we present RTK algorithms for long baselines more than 100 km with estimating tropospheric delays. The state vector is estimated by the extended Kalman filter. We show the experimental results of GPS RTK for various baselines (162.10, 393.37, 582.29, and 1283.57 km) by using the Korea Astronomy and Space Science Institute GPS data and one International GNSS Service (IGS) reference station located in Japan. As a result, we present that long baseline GPS RTK can provide the accurate positioning for users less than few centimeters.

• 한국측량학회지
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• 제21권2호
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• pp.123-129
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• 2003

본 논문에서는 동일한 GPS 측량 데이터를 Bernese GPS 소프트웨어로 기선 해석한 결과와 범용 상용 소프트웨어로 기선 해석한 결과를 비교 분석하였으며 장기선 데이터 처리시 고려해야 할 사항들을 검토하였다. Bernese GPS 소프트웨어로 장기선 데이터 처리시 기선 거리에 따른 편차가 거의 없는데 비해 범용 상용 소프트웨어로 장기선 데이터 처리시에는 기선 거리에 비례하여 편차가 발생하였다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.27-31
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• 2003

Underwater acoustic navigation systems are classified into three systems: ultra-short baseline (USBL), short baseline (SBL), and long baseline (LBL). Because the USBL system estimates the angle of a submersible, the estimation error becomes large if the submersible is far from the USBL transducer array mounted under a support vessel. SBL and LBL systems estimate submersible's location more accurately because they have wider distribution of measuring sensors. Especially LBL systems are widely used as a navigation system for deep ocean applications. Although it is most accurate system it still has estimation errors because of noise, measurement error, refraction and multi-path of acoustic signal, or wrong information of the distributed transponders. In this paper the estimation error of the LBL system are analyzed from a point of sensitivity. It is assumed that the error exists only in the distance between a submersible and the transponders. For this purpose sensitivity of the estimated position with respect to relative distances between them is analyzed. The result says that estimation error is small if the submersible is close to transponders but not near the ocean bottom.

• Journal of Astronomy and Space Sciences
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• 제40권3호
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• pp.113-122
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• 2023

Although the Relative Global Navigation Satellite System (GNSS) positioning technique provides high accuracy, it has several drawbacks. The scarcity of control points, the long baselines, and using of ultra-rabid and rabid products increased position errors. This study has designed a New MATLAB Program that helps users automatically select suitable IGS stations related to the baseline lengths and the azimuth between GNSS points and IGS stations. This study presented criteria for the length of the baselines used in Egypt and an advanced estimated accuracy before starting the project. The experimental test studies the performance of the position accuracy related to the relation between three factors: observation session, final, rabid, and ultrarabid products, and the baseline lengths. Ground control point mediates Egypt was selected as a test point. Nine surrounding IGS stations were selected as reference stations, and the coordinates of the tested point were calculated based on them. Baselines between the tested point and the IGS stations were classified regarding proposal criteria. The coordinates of the tested point were obtained in different observation sessions (0.5, 1, 2, 4, 5, 6, 7, 7.5 h). The results indicated that the lengths of the baseline in Egypt were classified short (less than 600 km), medium (600-1,200 km), and long (greater than 1,200 km) and required a minimum observation time of 4, 5, and 7 h to obtain accuracy 10, 19, 48 mm sequentially. The position accuracy was superior for the rapid and the final than the ultra-rapid products by 16%. A short baseline was at the best case; there was a performance in position accuracy with a 57% deduction in observation time compared with the long baseline.

• Smart Structures and Systems
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• 제24권2호
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• pp.243-256
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• 2019

Determination of the most meaningful structural modes and gaining insight into how these modes evolve are important issues for long-term structural health monitoring of the long-span bridges. To address this issue, modal parameters identified throughout the life of the bridge need to be compared and linked with each other, which is the process of mode tracking. The modal frequencies for a long-span bridge are typically closely-spaced, sensitive to the environment (e.g., temperature, wind, traffic, etc.), which makes the automated tracking of modal parameters a difficult process, often requiring human intervention. Machine learning methods are well-suited for uncovering complex underlying relationships between processes and thus have the potential to realize accurate and automated modal tracking. In this study, Gaussian mixture model (GMM), a popular unsupervised machine learning method, is employed to automatically determine and update baseline modal properties from the identified unlabeled modal parameters. On this foundation, a new mode tracking method is proposed for automated mode tracking for long-span bridges. Firstly, a numerical example for a three-degree-of-freedom system is employed to validate the feasibility of using GMM to automatically determine the baseline modal properties. Subsequently, the field monitoring data of a long-span bridge are utilized to illustrate the practical usage of GMM for automated determination of the baseline list. Finally, the continuously monitoring bridge acceleration data during strong typhoon events are employed to validate the reliability of proposed method in tracking the changing modal parameters. Results show that the proposed method can automatically track the modal parameters in disastrous scenarios and provide valuable references for condition assessment of the bridge structure.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2002년도 창립 20주년기념 국제학술대회
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• pp.103-118
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• 2002

본 논문에서는 동일한 GPS 측량 데이터를 Bernese GPS 소프트웨어로 기선 해석한 결과와 범용 상용 소프트웨어로 기선 해석한 결과를 비교 분석하였으며 장기선 데이터 처리시 고려해야할 사항들을 검토하였다. Bernese GPS 소프트웨어로 장기선 데이터 처리시 기선 거리에 따른 편차가 거의 없는데 비해 범용 상용 소프트웨어로 장기선 데이터 처리시에는 기선 거리에 비례하여 편차가 발생하였다.

• 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.

• 대한공간정보학회지
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• 제5권2호
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• pp.153-167
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• 1997

GPS의 장거리 기선 측정정밀도를 분석하기 위해 한국에 2지점과 일본에 9지점을 선정하고 GPS 관측을 방송력과 정밀력을 이용하여 동시에 실시하여 정밀도를 비교 분석하였다. 그 결과 기선장이 100km이하인 경우 방송력과 정밀력의 정밀도는 0.1ppm보다 작게 나타났다 그러나 100km 이상의 경우에서는 정밀력의 정밀도가 방송력보다 우수하게 나타났으며, VLBI점과 비교해 볼 때 방송력을 이용할 경우 0.13ppm, 정밀력을 이용할 경우 0.04ppm으로 분석되었다. 본 연구의 결과는 앞으로 장거리 기선측정을 위한 GPS측량에 있어서 방송력과 정밀력의 이용에 대한 기본자료로 이용될 것으로 기대된다.