# _remote sensing_
## 3 Results
### Sisre  
Figure 7 shows the annual evolution of the daily SISRE and SISRE_ORB of BDS-3 D1 navigation messages in 2022. SISRE_ORB was generated by SISRE via deducting the influence of the clock error. The mean value and standard deviation of SISRE_ORB were 0.083 m and 0.040 m, respectively, and the 24 MEO satellites of BDS-3 had similar and stable daily variation trends. The mean value and standard deviation of SISRE were 0.508 m and 0.210 m, respectively. Via the comparison between SISRE and SISRE_ORB, it was obvious that the satellites presented different trends and fluctuations due to the strong influence of the clock error. For SISRE_ORB, which was mainly affected by the orbit radial error, there was a significant change in C19, and this was consistent with the performance of orbit accuracies in the radial direction. The RMS statistics of SISRE_ORB, SISRE, and 95%SISRE, which denote the 95% confidence level of SISRE, are listed in Table 4. Their 2022 values were 0.092 m, 0.556 m, and 0.920 m, respectively. At the same time, the RMS statistics of the 24 MEO satellites of BDS-3 are plotted in Figure 8. For each satellite, the accuracy variation of SISRE_ORB was consistent with that of the orbit in the radial direction, and the accuracy variations of SISRE  
Figure 6: BDS-3 clock error accuracy statistic of each satellite (unit: m). Mean value of the hydrogen atomic clock (green), mean value of the rubidium atomic clock (black), standard value of the hydrogen atomic clock (blue), standard value of the rubidium atomic clock (red), RMS value of the hydrogen atomic clock (brown), and RMS value of the rubidium atomic clock (purple). Figure 7: The daily accuracy (DOY 1-365, 2022) of SISRE and SISRE_ORB of the BDS-3 D1 navigation message (unit: m). Each satellite has its own color. and 95%SISRE were consistent with that of the clock error. This was because SISRE was mainly affected by the orbit radial error and clock error, and the accuracy of the former was one order of magnitude better than that of the latter. After deducting the influence of the clock error, the accuracy of SISRE was high and stable. Moreover, the annual evolution of SISRE was dominated by the satellite clock error. The satellites of C29 and C37 had the best accuracy of SISRE, and this was consistent with the accuracy results of the clock error. The annual RMS statistics results of the SISRE_ORB and SISRE of D1 and B-CNAV navigation messages as well as their comparison are listed in Table 5. The accuracy of SISRE_ORB from B-CNAV navigation messages was better than that of the D1. Due to the improvement in the orbit radical direction, the improvement ratio of SISRE_ORB reached 8.40%. Because SISRE was mainly affected by the satellite clock error, its improvement ratio was small. The improvement ratios of each satellite are plotted in Figure 9. For each satellite, the improvement ratio of SISRE_ORB was positive, and the improvement ratio of SISRE exhibited both positive and negative values. In this case, SISRE_ORB was mainly affected by the orbit radial error, while SISRE was affected by the dual effects of the orbit radial error and clock error. The reference standards for the SISRE of D1 and B-CNAV navigation messages were not more than 1.0 m and 0.6 m, respectively [2]. For D1, the analyzed SISRE was 0.556 m, which was better than the reference value (1.0 m). For B-CNAV, the analyzed SISRE was 0.508 m, which was better than the reference value (0.6 m). It was obvious that the SISRE of BDS-3 MEO was better than its reference standard. \begin{table}
\begin{tabular}{c c c c} \hline
**TYPE** & **SISRE_ORB** & **SISRE** & **95\%SISRE** \\ \hline BDS-3 MEO & 0.092 & 0.556 & 0.920 \\ \hline \end{tabular}
\end{table} 
Table 4: The RMS statistics of SISRE_ORB, SISRE, and 95%SISRE of the D1 navigation message (units: m). Figure 8: The RMS statistics of SISRE_ORB, SISRE, and 95%SISRE of the D1 navigation message, for every satellite (unit: m): 95% SISRE RMS (blue), SISRE (orbit, clock, and bias errors), RMS (green), and orbit-only SISRE RMS (purple).