Nowadays, Global Navigation Satellite Systems (GNSS) data are used in most of the geodetic studies. Positioning information can be obtained by using GPS, GLONASS, Galileo and BeiDou in the structure of the GNSS. International GNSS Service (IGS) has initiated a project, called Multi-GNSS Experiment (MGEX), to collect, track and analyze different signals and satellite system data. Since, the Multi-GNSS solutions have started to use, positioning accuracy obtained from Multi-GNSS solutions is very important for users. Therefore, in this study, GNSS data of 10 stations were analyzed in 4 different scenarios as GPS, GPS/GLONASS, GPS/GLONASS/Galileo and GPS/GLONASS/Galileo/BeiDou. The GNSS data were processed using Trimble RTX service which is a web based precise point positioning (PPP) software that is capable of processing Multi-GNSS data. Results have demonstrated that, it has been shown that the higher positioning accuracy can be obtained using different satellite systems together, instead of using GPS-Only. Moreover, accuracy of Multi-GNSS solutions was investigated whether it depends on session duration and latitude or not. According to the results, it was emphasized that accuracy of Multi-GNSS solutions only depends on session duration.

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<p>Global Navigation Satellite Systems (GNSS) can be operated 24 hours in all weather conditions; thus, it is widely preferred in many geodetic studies. With GNSS, position information can be obtained with high accuracy. However, in order to achieve precise position, GNSS error sources such as atmospheric effects should be eliminated. Since ionospheric delay depends on the frequency of the transmitted signal, it can be eliminated with dual-frequency receivers. But, the tropospheric delay does not depend on the signal frequency. Therefore, it can not be eliminated by signal combinations. The effect of tropospheric delay depends on various factors such as station’s altitude, signal direction, cut off angle, atmospheric pressure, temperature and relative humidity. Although tropospheric delays occur along the signal path, these delays are estimated in zenith direction. Tropospheric mapping functions (MFs) are used to project slant to zenith delay. In this study, the effects of most preferred MFs in the literature, which are Global Mapping Function (GMF), Niell Mapping Function (NMF) and Vienna Mapping Function 1 (VMF1), on position accuracy was investigated. For this aim, three networks with different baseline lengths, (1) less than 100 km, (2) between 100 km and 500 km and (3) more than 500 km, were designed including 10 stations. In addition, to examine the seasonal effect of the MFs, four month dataset (January – April – July – October) were selected. These dataset were processed with the Bernese software implementing relative point positioning method by fixing 3 stations. Moreover, the dataset were subdivided into different session durations (2-3-4-6-8-12 and 24 hours) and the effect of session duration on position accuracy was analysed. According to the initial results, it can be concluded that the position accuracy on short session duration depends on the baseline length and more accurate results were obtained in the shortest network. In addition, more accurate results were obtained by VMF1 for the up component; however, for the horizontal components, there were no significant differences between the MFs.</p><p> </p><p><strong>Keywords:</strong> GPS, Accuracy, Troposphere, Mapping Functions, Bernese</p>