## 4 Galileo Augmenting GPS SFSE Precise Positioning Experiment
### Experiment Analysis
#### 4.2.2 Experiment 2  
For comparison, we processed another baseline data, of which the rover station is located in the middle span of the bridge, which is the most evident part reflecting the vibration of the bridge. Generally, since the deformation of the bridge is relatively large, the obtained position deviation includes both the random position error and the bias that is caused by the deformation. In the former set of data, since the mobile station is at the most stable position of the bridge, its positional deviation is basically only affected by random noise. However, in this set of data, the position deviation is mainly caused by the vibration and deformation of the bridge. Moreover, the height difference between the two stations is only 18m, which means that the tropospheric delays in this experiment can be ignored. The position deviation of the successful epochs with different strategies for baseline shm1-shm2 is shown in Figure 7, Figure 8 presents the curves of the corresponding NOS, ADOP, and Brt, and all evaluation indicators are given in Table 4. Similar to the former baseline, the combination of GPS and Galileo can provide more observational redundancy and increase the precision of the float solution for each epoch; the baseline length constraint method can improve the ambiguity resolution by limiting the baseline length and ambiguity search space for some erroneous epochs. The combination of the two methods will inevitably result in a higher success rate of baseline solution and a more realistic baseline relative position. As we can see from Figure 7, C-GPS improves the Asrt by around 16 pm and GPS/Galileo acts by around 5 am. The Asrt of the two methods are 97.57% and 98.42%, which are 4.33% and 5.18% higher than that of the single GPS. When the C-GPS/Galileo method is adopted, the Asrt of ambiguity resolution is up to 99.76%. This shows that the C-GPS/Galileo method is an effective approach in achieving high accuracy and high success rate baseline resolution in the field of bridge deformation. Figure 8: Mean NOS, ADOP, and bootstrapped success rates of different strategies for baseline shm1-shm2: (**a**) GPS, (**b**) C-GPS, (**c**) GPS/Galileo, and (**d**) C-GPS/Galileo. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **NOS** & **PDOP** & **ADOP** & **Asrt** & **Bstst** & \
\begin{tabular}{c} **Horizontal** \\ **Deviation/cm** \\ \end{tabular} &
\begin{tabular}{c} **Up** \\ **Accuracy/cm** \\ \end{tabular} \\ \hline GPS & 8.9 & 1.89 & 0.453 & 0.9324 & 0.9499 & 11.57 & 3.23 \\ C-GPS & 8.9 & 1.89 & 0.437 & 0.9757 & 0.9619 & 11.66 & 3.24 \\ GPS/Galileo & 12.3 & 1.48 & 0.250 & 0.9842 & 0.9958 & 11.67 & 3.17 \\ C-GPS/Galileo & 12.3 & 1.48 & 0.247 & 0.9976 & 0.999 & 11.78 & 3.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: NOS, PDOP, ADOP, success rate and position deviation of different strategies for baseline shm1-shm2. Figure 7: Position deviation of different strategies for baseline shm1-shm2: (**a**) GPS, (**b**) C-GPS, (**c**) GPS/Galileo, and (**d**) C-GPS/Galileo. In addition, it should be noted that the horizontal deviation of this set of baselines exceeds 1 decimeter, not only far beyond the horizontal deviation of the normal static baseline, but also much larger than the vertical deviation, which should be larger under normal circumstances. This undoubtedly illustrates that the rover station in the middle of the bridge keeps the vibration of the bridge well, and thus this set of data is greatly affected by the vibration of the bridge, especially in the easterly direction, as we can see in Figure 7. Therefore, enhancing the model of the observation equation does not certainly reduce the deviation of the baseline result, which is reflected in Table 4, but it increases the reliability of the ambiguity resolution. Moreover, it is obvious that the Asrt of single GPS in this experiment is about 18% more than that in experiment 1, because the tropospheric residuals in experiment 1 are larger.