The effect of Galileo satellite system on point positioning

Global Navigation Satellite System (GNSS) is the standard generic term for positioning with satellites. With a GNSS receiver, point position (latitude, longitude and altitude) can be determined using signals from satellites in the field of view. The use of multiple GNSS satellites and the increase in their number have increased the accuracy and precision of the calculated point positions. Today; The United States' Global Positioning System (GPS), Russia's Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS), European Space Agency's (ESA) Galileo, China's BeiDou satellites are used in global positioning studies. A few countries also have various geolocation systems within their regional coverage. These; India's Indian Regional Navigational Satellite System (IRNSS) and Japan's Quasi-Zenith Satellite System (QZSS). Thanks to these developments in satellite systems, it has been possible to determine geodetic point positions with higher accuracy than terrestrial techniques. Until recently, point positions in satellite-based systems were determined using GPS and GLONASS satellite systems. As of 2020, the Galileo satellite system has also started to be used in full operation. Today, regional position changes after earthquakes can be predicted by using GNSS. The accuracy in determining point positions with GNSS depends on the satellite system used, evaluation software, data collection intervals, data logging intervals, etc. varies depending on the effects. In this study, the effect of Galileo satellite system on point positioning was investigated depending on the data collection intervals. In this context, daily RINEX data of 7 of Turkish Permanent GPS Network (TURPEGN) stations (AKHI, BOZU, CINC, ESME, MNTS, SHUT, TVAS) selected between October, 15th 2020 - November, 13th 2020. The RINEX data have been divided into 2-, 4- and 12-h time intervals. The solutions were evaluated according to GPS only, GLONASS only, Galileo only and GPS+GLONASS+Galileo (MIX) satellite combinations in GAMIT/GLOBK data evaluation software. In the evaluations, 24-h RINEX data of 14 stations of international GNSS Stations (IGS) was also used. The 2-, 4- and 12-h RINEX data were obtained by choosing the earthquake occurrence time as the center. As a result of the evaluations, the approach of other satellite combinations to these coordinates was examined based on the daily coordinates obtained only with the GPS satellite combination. In the analysis, the closest results to the GPS coordinates are obtained a satellite combinations of MIX, Galileo only and GLONASS only, respectively. Then, the daily solutions obtained in order to reveal the effect of the İzmir-Seferihisar Earthquake dated 30 October 2020 on the TUSAGA stations in the region are divided into 2 parts as pre-earthquake and post-earthquake. With the t-test, the compatibility of the average coordinates before/after the earthquake was investigated. As a result of the research, these were concluded that the changes before and after the earthquake were mostly in the MNTS station, which is the closest to the earthquake center, that the changes in the points generally decrease as you move away from the earthquake center, and that the evaluation before and after the earthquake can be made more healthy as the measurement time increases. In addition, the ~30-day coordinates of the selected TURPEGN stations were also examined with the help of time series, and the change of the MNTS station closest to the earthquake center according to the pre- and post-earthquake period is given in the text, and the changes of other points are given in Appendix 1.