# Application of Multi-System Combination Precise Point Positioning in Landslide Monitoring
## 5 Application of Multi-System Combination PPP in Landslide Monitoring
### Analysis of Convergence Time  
Combined with the data quality test results of monitoring points and the preliminary experimental conclusions, the GPS system was used as the benchmark to carry out the multi-system combined PPP calculation experiment. It used G/R/C, G/R/E and G/R/E/C as three good combinations and the static relative positioning calculation coordinate value as the reference coordinate to verify the positioning performance and reliability of G/R/C, G/R/E and G/R/E/C combined PPP. As the calculated results of the observed data are basically similar, the position deviation and observation status of the observed data on the  
Figure 4: Landslide scope and monitoring point layout.  
Figure 5: Location of the monitoring site.  
According to the analysis of Figures 6-8, the G/R/C combination observation state is good, the average number of available satellites is 20.6, the average PDOP value is 1.36, and the three directions of NEU converge to within 0.1 m after 12.5, 14 and 30.5 min, respectively. After convergence, the positioning accuracy of N direction is better than 1 cm, E direction is better than 2 cm, and U direction is better than 5 cm. The observation state of the G/R/E combination is slightly worse: the average number of available satellites is 12.4, and the average PDOP value is 1.79. After 12.5, 13.5 and 33 min, the three directions of NEU converge to within 0.1 m. After convergence, the positioning accuracy of N direction is about 1 cm, E direction is better than 2.2 cm, and U direction is better than 5 cm. Because the station is located in the Fujian province, Galileo has fewer visible satellites, G/R/E/C composite state of observation is similar to G/R/C composite, the average number of available satellites is 21.1, and the average PDOP value of 1.35. The three directions of NEU converge to within 0.1 m after 12.5, 14 and 30.5 min, respectively. After convergence, the positioning accuracy of N direction is better than 1 cm, E direction is better than 2 cm, and U direction is better than 5 cm. In summary, the PPP convergence time of multi-system combination is basically the same, and the positioning accuracy of NEU in all three directions can reach centimeter level after about 30 min.  
In the combined PPP solution of multi-day GNSS monitoring data, if data stitching is not carried out, the daily observation data will experience about 30 min of initialization time, causing a serious waste of the original observation data. Therefore, it is extremely important to mosaic the multi-day data. In this study, the CHCData Mosaic software provided by Huace Navigation was used to mosaic the original observation data of the monitoring point, and the multi-system combined PPP calculation experiment was carried out, which greatly improved the utilization rate of the original observation. Figure 9 shows the solution results of the observation data stitching on the third and fourth days of the G/R/C, G/R/E and G/R/E/C combinations, respectively. The solid black line at the 2880 epoch is the splice point of observation data in the two phases. According to the analysis of Figure 9, the positioning accuracy of the combination of G/R/C and G/R/E/C in the N direction is better than 1 cm, the E direction is better than 2 cm, and  
Figure 8: Position deviation and observation of G/R/E/C combined PPP.  
the U direction is better than 5 cm after the PPP convergence. After the convergence of the G/R/E combination PPP, the positioning accuracy in the N direction is about 1 cm, the positioning accuracy in the E direction is better than 2.2 cm, and the positioning accuracy in the U direction is better than 5 cm.