• 한국측량학회지
• /
• 제27권1호
• /
• pp.693-700
• /
• 2009

장기선 네트워크 RTK(Real-Time Kinematic) 측량, 정밀단독측위(precise point positioning) 및 전리층/대류권 지연 모니터링등 GPS를 이용한 실시간 데이터 처리를 위해서는 IGS(International GNSS Service)에서 제공하는 정밀궤도 수준의 정확도가 시간지연 없이 확보되어야 한다. 본 연구는 준 실시간 위성궤도결정을 위한 선행연구로서 일반적인 위성궤도 결정 방법, 특히 동역학적 방법에 대한 이론적 고찰과 가속도 적분을 위한 지구기준/관성좌표계 변환 방법에 대한 테스트를 수행하였다. IAU 1976/1980 세차/장동모델은 IAU 2000A 모델과 0.05mas 수준의 허용범위 내 차이를 보였다. IAU 2000A 모델은 기본적으로 복잡한 장동모델로 인해 변환행렬 계산에 많은 시간이 소요된다. IAU 2000A 모델에 기존 변환 방법을 사용하는 경우가 NRO(non-rotating origin) 방법에 비해 2배정도 빠른 결과를 보인 반면 회전행렬의 실질적인 차이는 없는 것으로 나타났다.

• 한국정보통신학회논문지
• /
• 제19권5호
• /
• pp.1055-1062
• /
• 2015

본 논문에서는 GPS 위치 정보를 이용한 파고계측시스템을 제안한다. 제안한 시스템은 이중주파수 측정치 및 GPS 정밀위성정보를 이용하여 위치를 추정하는 PPP 기반 항법 알고리즘을 사용한다. 이를 이용하여 기준국으로부터 보정정보를 받는 RTK나 DGPS 기반 파고계와 달리 기준국과의 거리에 관계없이 높은 정확도로 위치 추정이 가능하다. 그리고 GPS 단독으로 운용되는 간단한 시스템이므로, 가속도계 기반 파고 계측 시스템처럼 다른 센서를 이용하여 누적되는 위치 오차를 보정할 필요가 없다. 제안한 파고계측시스템을 테스트하기 위하여 경북 울진 죽변항 인근 해역에 제안한 시스템과 기상청에서 활용하는 상용 파고계를 탑재한 부표를 설치하고, 시험 운용하였다. 그리고 부표로부터 전송된 두 가지 파고 데이터를 상호 비교함으로써 제안한 시스템의 성능을 평가하였다.

• Journal of Positioning, Navigation, and Timing
• /
• 제10권4호
• /
• pp.279-289
• /
• 2021

GNSS receivers capable of tracking multiple Global Navigation Systems (GNSSs) simultaneously are widely used. In order to estimate accurate user position and velocity, it is necessary to consider the key elements that contribute to the interoperability of the different GNSSs. Typical examples are the time system and the coordinate system. Each GNSS is operated based on its own reference time system depending on when the system was developed and whether the leap seconds are applied. In addition, each GNSS is designed based on its own coordinate system based on earth model constant values. This paper addresses the interoperability issues from the viewpoint of Single Point Positioning (SPP) users utilizing multiple GNSS signals from GPS, GLONASS, BeiDou, and Galileo. Since the broadcast ephemerides of each GNSS are based on their own time and coordinate systems, the time and the coordinate systems should be unified for any user algorithm. For this purpose, this paper proposes a method of converting each GNSS coordinate system into the reference coordinate system through Helmert transformation. The error of the broadcast ephemerides was calculated with the precise ephemerides provided by the International GNSS Service (IGS). The effectiveness of the proposed multi-GNSS correction and transformation method is verified using the Multi-GNSS Experiment (MGEX) station data.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
• /
• pp.751-756
• /
• 2002

Since the operation of the first satellite-based navigation services, satellite positioning has played an increasing role in both surveying and navigation, and has become an indispensable tool for precise relative positioning. However, in some situations, e.g. at a low angle of elevation, the use of satellites for navigation is seriously restricted because obstacles like buildings and mountains can block signals. As a mean to resolve this problem, the quasi-zenith satellite system has been proposed as a next-generation satellite navigation system. Quasi-zenith satellite is a system which simultaneously deploys several satellites in a quasi-zenith geostationary orbit so that one of the satellites always stay close to the zenith if viewed from a specific point on the ground of East Asia. Thus, if a position measurement function compatible with GPS is installed in the quasi-zenith and stationary satellites, and these satellites are utilized together with the GPS, four satellites can be accessed simultaneously nearly all day long and a substantial improvement in position measurement, especially in metropolitan areas, can be achieved. The purpose of this paper is to evaluate the effectiveness of quasi-zenith satellite system on positioning accuracy improvement through simulation by using precise orbital information of the satellites and a three-Dimensional digital map. Through this simulation system, it is possible to calculate the number of simultaneously visible satellites and available area of the positioning without the need of actual observation.

• Journal of Positioning, Navigation, and Timing
• /
• 제12권3호
• /
• pp.215-228
• /
• 2023

The State Space Representation (SSR) method provides individual corrections for each Global Navigation Satellite System (GNSS) error components. This method can lead to less bandwidth for transmission and allows selective use of each correction. Precise Point Positioning (PPP) - Real-Time Kinematic (RTK) is one of the carrier-based precise positioning techniques using SSR correction. This technique enables high-precision positioning with a fast convergence time by providing atmospheric correction as well as satellite orbit and clock correction. Currently, the positioning service that supports PPP-RTK technology is the Quazi-Zenith Satellite System Centimeter Level Augmentation System (QZSS CLAS) in Japan. A system that provides correction for each GNSS error component, such as QZSS CLAS, requires monitoring of each error component to provide reliable correction and integrity information to the user. In this study, we conducted an analysis of the performance of residual error bounding for each error component. To assess this performance, we utilized the correction and quality indicators provided by QZSS CLAS. Performance analyses included the range domain, dispersive part, non-dispersive part, and satellite orbit/clock part. The residual root mean square (RMS) of CLAS correction for the range domain approximated 0.0369 m, and the residual RMS for both dispersive and non-dispersive components is around 0.0363 m. It has also been confirmed that the residual errors are properly bounded by the integrity parameters. However, the satellite orbit and clock part have a larger residual of about 0.6508 m, and it was confirmed that this residual was not bounded by the integrity parameters. Users who rely solely on satellite orbit and clock correction, particularly maritime users, thus should exercise caution when utilizing QZSS CLAS.

• Journal of Astronomy and Space Sciences
• /
• 제19권4호
• /
• pp.385-394
• /
• 2002

SLR(Satellite Laser Ranging)은 위성과 관측소간 거리를 가장 정밀하게 측정할 수 있는 시스템이다. 1964년 발사된 Beacon-B 위성의 궤도결정을 위해 SLR 기술이 처음 사용되었는데 거리측정 정밀도가 m 수준이었다. 현재 single shot 정밀도는 cm, NP(Normal Point)는 mm수준으로 발전하였다. 이 연구에서는 SLR을 이용한 궤도결정 알고리즘을 개발하여 GPS(Global Positioning System)-36위성의 정밀 궤도를 결정하였다. 알고리즘의 정밀도를 검증하기 위해 산출한 정밀 궤도를 IGS(International GPS Service)에서 제공하는 정밀 궤도력과 비교하였는데 74cm의 RMS(Root Mean Square)를 얻었다. 또한, SLR 시스템의 관측잔차 RMS는 55mm 미만으로 알려져 있지만 이 연구에서는 44mm 결과를 얻을 수 있었다.

• Journal of Biosystems Engineering
• /
• 제36권2호
• /
• pp.116-121
• /
• 2011

This study was conducted to develop a robust navigator which could be in positioning for precision farming through developing a plural GPS receiver with 4 sets of GPS antenna. In order to improve positioning accuracy by integrating GPS signals received simultaneously, the algorithm for processing plural GPS signal effectively was designed. Performance of the algorithm was tested using a simulation program and a fixed point on WGS 84 coordinates. Results of this study are aummarized as followings. 1. 4 sets of lower grade GPS receiver and signals were integrated by kalman filter algorithm and geometric algorithm to increase positioning accuracy of the data. 2. Prototype was composed of 4 sets of GPS receiver and INS components. All Star which manufactured by CMC, gyro compass made by KVH, ground speed sensor and integration S/W based on RTOS(Real Time Operating System)were used. 3. Integration algorithm was simulated by developed program which could generate random position error less then 10 m and tested with the prototype at a fixed position. 4. When navigation data was integrated by geometrical correction and kalman filter algorithm, estimated positioning erros were less then 0.6 m and 1.0 m respectively in simulation and fixed position tests.

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

• 한국정밀공학회지
• /
• 제12권7호
• /
• pp.19-25
• /
• 1995

Presently, along with the advance of high-technology, the precise measurement of linear displacement has become a staple requirement, and consequently the high resolution with submicron order has also been required in precise positioning and carriaging. In this paper, we advance a propose on a new type of laser encoder based on the principle of phase analysis of the moire fringes from superimposed two gratings. The phase angle as an information of displacement can be accurately calculated by detecting the change in brighness at four points of the fringes. The actual application of four point method to the moire fringes is performed thru microcomputer for general purpose, and the measuring procedure is also studied in this research. As an experimental result, in the case of using 20 .mu. m-pitch gratings, it is validated that this method has the resolution of 0.01 .mu. m and the accuracy of .+-. 0.15 .mu. m over the setting range of 100mm.