• Journal of Astronomy and Space Sciences
• /
• v.26 no.2
• /
• pp.199-210
• /
• 2009

Even though there are several Global Navigation Satellite Systems under development, only GPS and GLONASS are currently available for satellite positioning. In this study, GLONASS orbits were predicted from broadcast ephemeris using the 4th-order Runge-Kutta numerical integration. For accuracy validation, predicted orbits were compared with precise ephemeris. The RMS(Root Mean Square) and maximum 3-D errors were 14.3 km and 17.4 km for one-day predictions. In case of 7-day predictions, the RMS and maximum 3-D errors were 15.7 and 40.1 km, respectively. Also, the GLONASS satellite visibility predictions were compared with real observations, and they agree perfectly except for several epochs when the satellite signal was blocked by nearby buildings.

• Journal of Astronomy and Space Sciences
• /
• v.25 no.3
• /
• pp.267-282
• /
• 2008

The GNSS (Global Navigation Satellite System) signal is delayed by the neutral atmosphere at the troposphere, so that the delay is one of major error sources for GNSS precise positioning. The tropospheric delay is an integrated refractive index along the path of GNSS signal. The refractive index is empirically related to standard meteorological variables, such as pressure, temperature and water vapor partial pressure, therefore the tropospheric delay could be calculated from them. In this paper, it is presented how to generate meteorological data where observation cannot be performed. KASI(Korea Astronomy & Space Science Institute) has operated 9 GPS (Global Positioning System) permanent stations equipped with co-located MET3A, which is a meteorological sensor. Meteorological data are generated from observations of MET3A by Ordinary Kriging. To compensate a blank of observation data, simple models which consider periodic characteristics for meteorological data, are employed.

• Journal of Korean Society for Geospatial Information Science
• /
• v.8 no.1 s.15
• /
• pp.97-103
• /
• 2000

The main purpose of 1-1-9 Caller Location Information System is to identify and display the precise location of emergency incidents such as natural or man - made fires, medical emergencies and accidents. The state - of- the - art technologies such as Am (Automatic Number Identification), GIS(Geographical Information System) and GPS (Global Positioning System) were applied and integrated in the system for efficient and effective location identification. It displays a radius of 25M, 50M and 100M on the map after location identification. The system can also provide the shortest path to an incident location from a fire station or a fire engine. In case of a fire breakout in or near a building, the attribute information of the building, called a building attribute card, is displayed along with the map location. The system then matches the information with the fire situation and sends an alert to a responsible fire station by phone or fax in order to help promptly react to the problem. An attribute card includes the critical information of a premise such as building's location, number of stories, floor plans, capacity, construction history, indoor fire detection and Prevention facilities, etc.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• v.1
• /
• pp.179-184
• /
• 2006

Rapid and high-precision positioning with a Global Navigation Satellite System (GNSS) is feasible only when very precise carrier-phase observations can be used. There are two kinds of mathematical models for ambiguity resolution. The first one is based on both pseudorange and carrier phase measurements, and the observation equations are of full rank. The second one is only based on carrier phase measurement, which is a rank-defect model. Though the former is more commonly used, the latter has its own advantage, that is, ambiguity resolution will be freed from the effects of pseudorange multipath. Galileo will be operational. One of the important differences between Galileo and current GPS is that Galileo will provide signals in four frequency bands. With more carrier-phase data available, frequency combinations with long equivalent wavelength can be formed, so Galileo will provide more opportunities for fast and reliable ambiguity resolution than current GPS. This paper tries to investigate phase only fast ambiguity resolution performance with four Galileo frequencies for short baseline. Cascading Ambiguity Resolution (CAR) method with selected optimal frequency combinations and LAMBDA method are used and compared. To validate the resolution, two tests are used and compared. The first one is a ratio test. The second one is lower bound success-rate test. The simulation test results show that, with LAMBDA method, whether with ratio test or lower bound success rate validation criteria, ambiguity can be fixed in several seconds, 8 seconds at most even when 1 sigma of carrier phase noise is 12 mm. While with CAR method, at least about half minute is required even when 1 sigma of carrier phase noise is 3 mm. It shows that LAMBDA method performs obviously better than CAR method.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.29 no.2
• /
• pp.201-208
• /
• 2011

With the increase in the number of smartphone users, precise 3D positional information is required by various applications. The positioning accuracy using civilian single-frequency pseudoranges is at the level of 10 m or so, but most applications these days are asking for a sub-meter level Therefore, instead of an absolute positioning technique, the VRS-based differential approach is applied along with the correction of the double-differenced (DD) residual errors using FKP (Flachen-Korrektur-Parameter). The VRS (Virual Reference Station) is located close to the rover, and the measurements are generated by correcting the geometrical distance to those of the master reference station. Since the unmodeled errors are generally proportional to the length of the baselines, the correction parameters are estimated by fitting a plane to the DD pseudorange errors of the CORS network. The DD positioning accuracy using 24 hours of C/A code measurements provides the RMS errors of 37 cm, 28 cm for latitudinal and longitudinal direction, respectively, and 76 cm for height. The accuracy of the horizontal components is within ${\pm}0.5m$ for about 90% of total epochs, and in particular the biases are significantly decreased to the level of 2-3 cm due to the network-based error modeling. Consequently, it is possible to consistently achieve a sub-meter level accuracy from the single-frequency pseudoranges using the VRS and double-differenced error modeling.

• Journal of Navigation and Port Research
• /
• v.37 no.1
• /
• pp.71-77
• /
• 2013

Most of the maritime accidents are the crash that occurred by complex coastal terrain, increased maritime traffic and frequent weather changes. Therefore, transportation safety is exactly determined using accurate environmental informations, but if informations are inaccurate or insufficient, accident risk can be increased. Therefore, ship need the system that can accurately generate transportation safety information. This paper proposes the transportation safety system and performance evaluation in the real environment. The proposed system includes database of environment informations and navigation algorithm using PPP method to estimate the accurate ship position. Therefore, this system can accurately calculate distance or freeboard between ship with other factors. Futhermore, when weather is deteriorated, crew can sail with database based 3-D monitoring module in the transportation safety system. To verify the function and performance, data of Kyungin ARA waterway and ferry is used to evaluation.

• Journal of Advanced Navigation Technology
• /
• v.20 no.5
• /
• pp.425-432
• /
• 2016

When user estimates user's position, GPS positions can be obtained from the navigation message transmitted from the GPS. However, the broadcast ephemeris cannot be used in the applications required high-level accuracies because it can cause errors of several meters. To correct satellite positions and clocks, user can use RTS corrections provided by IGS. In this paper, the accuracy of broadcast and RTS corrections are analyzed by comparing with the IGS final for 3-months. The RTS errors are analyzed for each user's locations and satellite blocks. The correlations between errors and shadow condition, and solar and geomagnetic activities are analyzed. The latency is applied to the RTS corrections, and these are extrapolated by polynomial. Then, the extrapolated RTS are compared with true RTS. The single-day performances of the PPP by broadcast ephemeris and RTS corrected ephemeris are analyzed. As a result, RTS 3D orbit and clock errors are 1/20 and 1/3 less than broadcast ephemeris errors. 3D positioning error of the RTS is 1/5 less than that of broadcast ephemeris.

• Korean Journal of Remote Sensing
• /
• v.38 no.6_1
• /
• pp.1125-1139
• /
• 2022

In an unmanned aerial vehicles (UAVs) system, a physical offset can be existed between the global positioning system/inertial measurement unit (GPS/IMU) sensor and the observation sensor such as a hyperspectral sensor, and a lidar sensor. As a result of the physical offset, a misalignment between each image can be occurred along with a flight direction. In particular, in a case of multi-sensor system, an observation sensor has to be replaced regularly to equip another observation sensor, and then, a high cost should be paid to acquire a calibration parameter. In this study, we establish a precise sensor model equation to apply for a multiple sensor in common and propose an independent physical offset estimation method. The proposed method consists of 3 steps. Firstly, we define an appropriate rotation matrix for our system, and an initial sensor model equation for direct-georeferencing. Next, an observation equation for the physical offset estimation is established by extracting a corresponding point between a ground control point and the observed data from a sensor. Finally, the physical offset is estimated based on the observed data, and the precise sensor model equation is established by applying the estimated parameters to the initial sensor model equation. 4 region's datasets(Jeon-ju, Incheon, Alaska, Norway) with a different latitude, longitude were compared to analyze the effects of the calibration parameter. We confirmed that a misalignment between images were adjusted after applying for the physical offset in the sensor model equation. An absolute position accuracy was analyzed in the Incheon dataset, compared to a ground control point. For the hyperspectral image, root mean square error (RMSE) for X, Y direction was calculated for 0.12 m, and for the point cloud, RMSE was calculated for 0.03 m. Furthermore, a relative position accuracy for a specific point between the adjusted point cloud and the hyperspectral images were also analyzed for 0.07 m, so we confirmed that a precise data mapping is available for an observation without a ground control point through the proposed estimation method, and we also confirmed a possibility of multi-sensor fusion. From this study, we expect that a flexible multi-sensor platform system can be operated through the independent parameter estimation method with an economic cost saving.

• Journal of Advanced Navigation Technology
• /
• v.19 no.3
• /
• pp.199-206
• /
• 2015

For real-time precise positioning, IGS provides ephemeris predictions (IGS ultra-rapid, IGU) and real-time ephemeris estimates (real-time service, RTS). Due to the RTS data latency, which ranges from 5 s to 30 s, a short-term prediction process is necessary before applying the RTS corrections. In this paper, the real-time performance of the RTS correction and IGU prediction are compared. The RTS correction availability for the GPS satellites observed in Korea is computed as 99.3%. The RTS correction is applied to broadcast ephemeris to verify the accuracy of the RTS correction. The 3D orbit RMS error of the RTS correction is 0.043 m. Prediction of the RTS correction is modeled as a polynomial, and then the predicted value is compared with the IGU prediction value. The RTS orbit prediction accuracy is nearly equivalent to the IGU prediction, but RTS clock prediction performance is 0.13 m better than the IGU prediction.

• Journal of Navigation and Port Research
• /
• v.40 no.6
• /
• pp.385-390
• /
• 2016

ELoran Systems can provide Position, Navigation, and Time services with comparable performance to Global Positioning Systems (GPS) as a back up or alternative system. High timing and navigation performance can be achieved by eLoran signals because eLoran receivers use "all-in-view" reception. This incorporates Time of Arrival (TOA) signals from all stations in the service range because each eLoran station is synchronized to Coordinated Universal Time (UTC). Transmission station information and the differential Loran correction data are transmitted via an additional Loran Data Channel (LDC) on the transmitted eLoran signal such that eLoran provides improved Position Navigation and Timing (PNT) over legacy Loran. In this paper, we propose a technique for adapting the delay time compensation values in eLoran timing receivers to provide precise time comparison. For this purpose, we have designed a system that measures time delay from the crossing point of the third cycle extracted from the current transformer at the end point of the transmitter. The receiver delay was measured by connecting an active H-field, an E-field and a passive loop antenna to a commercial eLoran timing receiver. The common-view time transfer technique using the calibrated eLoran timing receiver improved the eLoran transfer time. A eLoran timing receiver calibrated by this method can be utilized in the field for precise time comparison as a GNSS backup.