# The Impact of Eclipsing GNSS Satellites on the Precise Point Positioning
## 3 Results and Discussion
### The Impact of Eclipsing Satellites on GNSS PPP
#### 3.3.4 The Effect of the Satellite Geometry Structure  
From the above analysis, the number of the visible satellites will significant influence the positioning accuracy and the convergence time for the single-system PPP, especially for the GLONASS-only (except stations in the high latitude regions) or BDS-only kinematic PPP mode. First, the number of eclipsing satellites for each system are investigated. In general, the satellites on the same orbital plane will successively enter into the eclipsing regimes, and the eclipsing period for more than one orbital plane happens very rarely. There are about 4-6 satellites distributed in one orbital plane for GPS. Due to the different sun angle limits of GPS IIR and IIF satellites, all GPS satellites on the same orbital plane will not be in the eclipsing period at the same time. The average percentage of eclipsing satellites for every day in July (the ration of the number of eclipsing satellites to that of all the constellation) can be computed according to the eclipsing monitoring results. As shown in the second column of Table 6, the average percentage of GPS among all the July is about 9.2% (approximately three GPS satellites). In the case of GLONASS, there are only three orbital planes, which means that the whole orbital plane (generally, in total eight satellites) are in the eclipsing period at the same time. During the experimental time, the average percentage of GLONASS among all the July is about 27.3%. This large proportion can also be accounted for the great influences of eclipsing satellites on the GLONASS-only PPP. Since the GALILEO and BDS are still at the stage of development, the number of satellites of each orbital plane are usually smaller than that of GPS/GLONASS. With the increasing number of the satellites, the geometric strength of the mathematical model is enhanced. At this time, the influence of the small amount of the eclipsing satellites will be weakened, especially for static PPP mode. As shown in the last six rows of Table 6, when multi-GNSS data are introduced into the PPP model, the positioning results of these three strategies are consistent in the static PPP mode. Different from the single-system kinematic PPP, deleting eclipsing satellites or using the modeled attitudes will slightly improve the multi-GNSS PPP positioning results. Compared with Figure 13c, the PDOP of GR in station AREG, shown in Figure 15, is so small that deleting eclipsing satellites will not result in a worse solution. The improvements of S3 in GR kinematic PPP mode are 3.18%, 1.64% and 2.91% in the north, east and up direction while the improvements of S3 in GREC kinematic PPP mode are 1.17%, 1.71% and 1.21%, respectively. As shown in the second column of Table 6, the percentage of the GPS/GLONASS eclipsing satellites is smaller than that of GLONASS. When data of four satellite system are available, the percentage of the eclipsing satellites is further decreased to 13%. The enough non-eclipsing satellites are benefit for decreasing the influences of the non-nominal attitudes. Therefore, the improvements of S1 and S2 are decreased with the satellite geometric strength. When observations of four systems are available, the improvements are non-significant. To further analyze the effect of the satellite geometry structure, the average convergence time and the percentage of convergence under different sessions (30 min and 60 min) are also shown in Table 7. For GPS-only PPP, deleting eclipsing satellites is helpful to improve the positioning accuracy, however, the mean convergence time is also affected and becomes slightly longer than that of S2. When it comes to multi-GNSS PPP mode, the mean convergence time of PPP is greatly reduced and the percentage of convergence within 30 min is also significantly increased. Compared with S2, both S1 and S3 of GR PPP can slightly reduce the mean convergence time. When data of the GALILEO and BDS are also introduced into PPP model, the reduction of the convergence time becomes further smaller.