# The Impact of Eclipsing GNSS Satellites on the Precise Point Positioning
## 3 Results and Discussion
### The Impact of Eclipsing Satellites on GNSS PPP
#### 3.3.1 The Impact on the Positioning Accuracy of the Single-System Static PPP  
The filter solutions at current epoch are the weighted average values of the prediction values and the current measurements. When the filter is not converged, the contributions of current measurements to the filter solutions are relatively large. At this time, the effects of the eclipsing satellites will be highlighted, possibly resulting in a worse solution and a longer convergence time. Because the coordinate parameters in static PPP are set as constant models, when the filter is converged fully, the prediction values are relatively accurate and the effects of the eclipsing satellites are weakened. The average RMS (Root Mean Square) values of the three eclipsing strategies for single-system PPP are shown in Table 6. The RMS computations for the north, east and up coordinate components are based on the positioning errors of all the converged epochs. For GPS-only static PPP, the positioning performances of three eclipsing strategies are almost the same. Compared to S2, the improvements of S1 and the S3 are trivial. Different from the GPS-only PPP, S1 and S3 of the GLONASS-only static PPP can achieve a better accuracy than that of S2. The improvements of S1 are 8.60%, 9.92% and 4.77% in the north, east and up direction, while the improvements of S3 are 11.20%, 12.3% and 6.43%, respectively. The main reasons for these improvements are the large PCO values and the long durations of the GLONASS satellites shadow crossing (54 min for GLONASS satellites). Due to the limited number of the visible satellites for the single-system PPP, deleting satellites may induce a poorer satellite  
Figure 10: The distribution of the selected GNSS stations (as of July 2017). geometry structure. Therefore, the improvements of S3 are greater than S1. Because the released time of the official attitude control model for GALILEO FOC satellites is later than the experimental time in this contribution, the nominal attitude or the IOV satellites' attitude may be adopted for the FOC satellites in the estimation of the precise orbit and clock products used in PPP. Therefore, using official attitude will not result in a better solution than that of the nominal attitude. It is not hard to find that deleting GALILEO satellites may reduce the satellite geometric strength because, on average, only 4-6 GALILEO satellites can be tracked for one station. It is worth noting that the eclipsing satellites have the greatest impact on the BDS-only static PPP. Compared with S2, using the modeled attitude can improve the positioning accuracy by about 34.99%, 38.34% and 22.39% in the north, east and up direction, respectively. Furthermore, deleting BDS eclipsing satellites can also improve the accuracy by 19.20%, 22.56% and 12.16% in the north, east and up direction, respectively. To further analyze the reason of the significant improvement for the BDS-only static PPP, the positioning performance of three eclipsing strategies and the phase residuals of S2 are shown in Figures 11 and 12. At the observation time, two BDS IGSO satellites are in eclipse. Their actual yaw angles are zero and the maximum yaw angle differences are 180\({}^{\circ}\). Due to the smaller average orbital angular velocity (0.00418\({}^{\circ}\)/s) of BDS IGSO satellites, the duration for maximum yaw angle differences is rather long, usually lasting for about several hours. At this time, large systematic errors caused by the non-nominal attitude will be brought into the phase residuals. The maximum residuals will reach up to 13 cm during the process of the filter convergence, which result in big deviations in the positioning solutions. This will also influence the positioning accuracy of the subsequent epochs for a long time, even after the convergence. It is also obvious to find that deleting these eclipsing satellites will induce a longer convergence time. Due to the smaller variation of the BDS satellites geometry structure, this phenomenon will be more obvious than other satellite systems.