The International GNSS Service (IGS) in April 2013 started real-time services (IGS-RTS) to provide access to high-precision products such as orbits, clocks and code observation errors. Products containing corrections are delivered to users by the RTCM data stream in real-time. The IGS03 stream which contains corrections for GPS and GLONASS systems is currently in the experimental stage and positioning with its use is still insufficiently investigated in terms of accuracy and reliability of positioning. In this paper we evaluate the impact of the IGS-RTS streams on positioning. In research section we presented the results of the processing of two-week satellite observations registered at five IGS stations located at different latitudes, using the three IGS-RTS streams: IGS01, IGS02 and IGS03, and BKG Ntrip Client (BNC). Post-processing involved the utilization of GPS and GPS+GLONASS signals. Subsequently we analyzed the real-time position determination of MARS IGS station using IGS03 data stream, which showed one of the best performance during the development of observation in post-processing mode. In analysis we applied approach showing the probability of achieving results within the assumed ranges of accuracy (<1.0 m, <0.5 m, <0.2 m, <0.1m). This approach allows the estimation of potential applications, depending on the expected accuracy of positioning.
In recent years, the Global Navigation Satellite Systems (GNSS) have been intensively modernized, resulting in the introduction of new carrier frequencies for GPS and GLONASS and the development of new satellite systems such as Galileo and BeiDou (BDS). For this reason, the absolute field antenna calibrations performed so far for the two legacy carrier frequencies, the GPS and GLONASS, seem to be insufficient. Hence, all antennas will require a re-calibration of their phase center variations for the new signals to ensure the highest measurement accuracy. Currently, two absolute calibration methods are used to calibrate GNSS antennas: field calibration using a robot and calibration in an anechoic chamber. Unfortunately, differences in these methodologies also result in a disparity in the obtained antenna phase center corrections (PCC). Therefore, we analyze the differences between individual PCC obtained with these two methods, specifically for the Leica AR-25 antenna model (LEIAR25). In addition, the influence of PCC differences on the GNSS-derived position time series for 19 EUREF Permanent GNSS Network (EPN) stations was also assessed. The results show that the calibration method has a noticeable impact on PCC models. PCC differences determined for the ionosphere-free combination may reach up over 20 mm and can be transferred to the position domain. Further tests concerning the positioning accuracy showed that for horizontal coordinates differences between solutions were mostly below 1 mm, exceeding 2 mm only at two stations for the GLONASS solution. However, the height component differences exceeded 5 mm for four, six and six stations out of 19 for the GPS, GLONASS and Galileo solutions, respectively. These differences are strongly dependent on large L2 calibration differences.
Among many sources of errors that influence Global Navigation Satellite System (GNSS) observations, tropospheric delay is one of the most significant. It causes nonrefractive systematic bias in the observations on the level of several meters, depending on the atmospheric conditions. Tropospheric delay modelling plays an important role in precise positioning. The current models use numerical weather data for precise estimation of the parameters that are provided as a part of the Global Geodetic Observation System (GGOS). The purpose of this paper is to analyze the tropospheric data provided by the GGOS Atmosphere Service conducted by the Vienna University of Technology. There are predicted and final delay data available at the Service. In real time tasks, only the predicted values can be used. Thus it is very useful to study accuracy of the forecast delays. Comparison of data sets based on predicted and real weather models allows for conclusions concerning possibility of using the former for real time positioning applications. The predicted values of the dry tropospheric delay component, both zenith and mapped, can be safely used in real time PPP applications, but on the other hand, while using the wet predicted values, one should be very careful.
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