## 3 Results
### Consistency of Precise Products from Different Analysis Centers
#### 3.3.4 BDS  
Figure 6 depicts the epoch-wise orbit and clock differences between GFZ and WHU precise products for BDS-2 GEO and IGSO satellites on DOY 122 of 2020. Most orbit differences of BDS-2 IGSO satellites range from 0.3 to 0.3 m for all the three orbital components. As for BDS-2 GEO satellites, the radial orbit differences also vary within 0.3 m, but the orbit differences can exceed 1 and 2 m in the cross-track and along-track components for several satellites, respectively. Except for C06 satellite, the clock differences of BDS-2 GEO and IGSO satellites have a varying range of 1.0 ns. Figure 7 depicts the corresponding results for BDS-2 MEO and BDS-3 MEO satellites. The fluctuation range of orbit differences for BDS MEO satellites is reduced to approximately 8, 15 and 15 cm in the \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Items**} & \multirow{2}{*}{**ACs**} & \multicolumn{4}{c}{**ACs**} \\ \cline{3-5}  & & **GFZ** & **WHU** & **CNES** \\ \hline \multirow{3}{*}{Radial (cm)} & ESA & 1.9 & 2.3 & 3.0 \\  & GFZ & – & 2.2 & 2.7 \\  & WHU & – & – & 3.2 \\ \hline \multirow{3}{*}{Along-Track (cm)} & ESA & 2.4 & 3.1 & 4.7 \\  & GFZ & – & 3.9 & 5.3 \\  & WHU & – & – & 5.8 \\ \hline \multirow{3}{*}{Cross-Track (cm)} & ESA & 2.5 & 3.7 & 3.7 \\  & GFZ & – & 4.6 & 4.2 \\  & WHU & – & – & 5.6 \\ \hline \multirow{3}{*}{Clock (ns)} & ESA & 0.06 & 0.06 & 0.19 \\  & GFZ & – & 0.08 & 0.19 \\ \cline{1-1}  & WHU & – & – & 0.19 \\ \hline \multirow{3}{*}{SISRE (cm)} & ESA & 1.7 & 1.9 & 5.4 \\  & GFZ & – & 2.3 & 5.3 \\ \cline{1-1}  & WHU & – & – & 5.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: RMSs of epoch-wise differences of precise satellite orbit and clock corrections among different ACs as well as SISRE statistics for Galileo satellites. Figure 5: Epoch-wise orbit and clock differences for Galileo satellites between GFZ and WHU precise products on DOY 122 of 2020.  
radial, cross-track and along-track components, respectively, and the corresponding clock differences nearly always keep within 0.5 ns. The uneven distribution of tracking stations for BDS GEO and IGSO satellites will result in a weak geometric configuration between stations and satellites, which can obviously affect the accuracy of precise orbit and clock products. The statistical inconsistency results of precise satellite products for BDS-2 GEO and IGSO satellites are exhibited in Table 5. It is noted that the precise products from ESA  
Figure 6: Epoch-wise orbit and clock differences for BDS-2 GEO and IGSO satellites between GFZ and WHU precise products on DOY 122 of 2020. Figure 7: Epoch-wise orbit and clock differences for BDS-2 and BDS-3 MEO satellites between GFZ and WHU precise products on DOY 122 of 2020.  
do not support the BDS-2 GEO satellites. The orbital difference in the along-track and cross-track directions of BDS-2 GEO satellites can be larger than 1 m, especially for the along-track orbit difference with a value of 324.1 and 355.3 cm between CNES and GFZ, and CNES and WHU, respectively. The radial orbit difference of BDS-2 GEO satellites between WHU and GFZ precise products decreases to 15.2 cm, and the RMSs of clock difference are 0.39 ns, both of which seem to be at an acceptable level, but the corresponding statistics are increased by a factor of about three and two times for the inconsistency results between the real-time and post-processed products, respectively. Regarding the SISRE statistics, the consistency of precise products of BDS-2 GEO satellites between WHU and GFZ is 22.1 cm, while the corresponding consistency between the real-time and post-processed products decreases to 54.4-55.2 cm. Compared with the BDS-2 GEO satellites, the consistency results of BDS-2 IGSO satellites are significantly improved, especially for the along-track and cross-track orbit differences.