## 3 Materials and Methods  
### The Test Area and Data Collection  
A kinematic test was performed in June 2017 on Obruk Lake Dam, Corum province of Turkey (Figure 2, left). In this experiment, a vessel equipped with Trimble R10 multi-frequency multi-constellation GNSS receivers with compact antenna was used. 440-channels R10 receivers are capable of simultaneously tracking GPS, GLONASS, Galileo, BDS, QZSS, and NavIC (IRNSS). It provides high-rate positioning with 1 s (1 Hz), 0.5 s (2 Hz), 0.2 s (5 Hz), 0.1 s (10 Hz), and 0.05-s (20 Hz) positioning rates. The GNSS positioning accuracy is given as (3 mm + 0.1 ppm RMS (H)) and (3.5 mm + 0.4 ppm RMS (V)) for Static Surveying; (8 mm + 1 ppm RMS (H)) and (15 mm + 1 ppm RMS (V)) for Real-time Single-Baseline Kinematic Surveying (<30 km); and (8 mm + 0.5 ppm RMS (H)) and (15 mm + 0.5 ppm RMS (V)) for Network RTK. The R10 provides \(\pm\)2 cm RMS horizontal and \(\pm\)5 cm RMS vertical accuracy with the Trimble CenterPoint RTX correction service as RT-PPP using satellite delivery or internet connection anywhere in the world. More information about the Trimble R10 receiver can be found in [32]. The kinematic test data were collected for approximately 6 h (about 21,350 measurement epochs) from all visible GPS, GLONASS, Galileo, and BDS satellites in view with 1-s positioning rate. The satellite elevation mask angle was set to 10\({}^{\circ}\). The trajectory of the surveying vessel during the kinematic test is shown in Figure 2, right.  
The number of the tracked satellites and the average number of tracked satellites and calculated PDOP (Position Dilution of Precision) values during the kinematic test were given in Figure 3 and Table 2, respectively. According to Figure 3 and Table 2, the average number of the tracked satellites and calculated PDOPs are 8 and 2.0 for GPS-only; 14 and 1.8 for GPS and GLONASS combinations; 18 and 1.5 for GPS, GLONASS, and Galileo combinations; 19 and 1.5 for GPS, GLONASS, and BDS combinations; and 23 and 1.2 for GPS, GLONASS, Galileo, and BDS combinations, respectively.  
In order to give an idea about the collected data quality, the Multipath and SNR (Signal-to-Noise Ratio) graphics for the carrier frequencies in the constellations were created and given as sky-plot in the Figure 4. According to plots in Figure 4, it is clearly seen that all SNR values are over the limit that is 35 dBHz, except GPS L2, and the multipath values are less than 0.60 m for both frequencies in all constellations. According to the collected data, Figure 4 shows that GPS L1 frequency signal is more powerful than L2 frequency, and L2 multipath values are bigger than L1 values. Both Galileo signals have the best SNR values and small multipath values among all constellations.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Satellite System:** & **G** & **G+R** & **G+R+E** & **G+R+C** & **G+R+E+C** \\ \hline
**Number of Sat. (averaged):** & 8 & 14 & 18 & 19 & 23 \\
**PDOP (averaged):** & 2.0 & 1.8 & 1.5 & 1.5 & 1.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Average number of tracked satellites and PDOPs.  
Figure 3: Number of tracked GNSS satellites during the kinematic test.  
Figure 2: Test measurement (**left**) and the trajectory of the survey vessel (**right**).