## 5 Results
### Impact of Tracking Geometry  
In order to investigate the impact of the tracking geometry, we defined four tracking networks: Chinese regional network (CHN), Asian-Pacific network (AP), Asian network (ASIA), and global network (ALL). The data are processed using an identical strategy. The resulting orbit overlaps RMS for each satellite over the seven weeks, are listed in Table 6, where the columns are sorted first by components then by networks. The 3D-RMS are also illustrated in Figure 8.  
From the averaged 3D-RMS, in the AP network (adding PETH and SIGP to CHN network) the overlapping RMS for GEOs gets even slightly worse, but brings about 15% improvement for IGSOs. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Component**} & \multicolumn{3}{c}{**Along**} & \multicolumn{3}{c}{**Cross**} & \multicolumn{3}{c}{**Radial**} & \multicolumn{3}{c}{**3D**} \\ \hline  & & ALL & ASIA & AP & CHN & ALL & ASIA & AP & CHN & ALL & ASIA & AP & CHN & ALL & ASIA & AP & CHN \\ \hline \multirow{6}{*}{GEO} & C01 & 164 & 169 & 169 & 176 & 11 & 18 & 16 & 22 & 6 & 7 & 8 & 8 & 164 & 170 & 170 & 178 \\  & C03 & 41 & 57 & 460 & 331 & 11 & 17 & 20 & 21 & 5 & 6 & 9 & 9 & 43 & 60 & 461 & 332 \\  & C04 & 162 & 208 & 171 & 182 & 12 & 24 & 17 & 24 & 9 & 12 & 13 & 12 & 163 & 210 & 172 & 184 \\  & C05 & 86 & 80 & 485 & 529 & 11 & 26 & 23 & 48 & 6 & 8 & 26 & 31 & 87 & 84 & 486 & 532 \\ \cline{2-15}  & Mean & 113 & 128 & 321 & 304 & 11 & 21 & 19 & 29 & 7 & 8 & 14 & 15 & 114 & 130 & 322 & 306 \\ \hline \multirow{6}{*}{IGSO} & C06 & 28 & 36 & 41 & 39 & 17 & 23 & 32 & 33 & 8 & 11 & 11 & 12 & 34 & 44 & 53 & 52 \\  & C07 & 31 & 69 & 40 & 83 & 18 & 31 & 29 & 45 & 7 & 14 & 10 & 15 & 37 & 77 & 50 & 96 \\ \cline{1-1}  & C08 & 27 & 50 & 43 & 48 & 18 & 28 & 26 & 32 & 11 & 26 & 18 & 24 & 34 & 63 & 53 & 62 \\ \cline{1-1}  & C09 & 23 & 30 & 39 & 36 & 14 & 22 & 26 & 33 & 8 & 10 & 10 & 11 & 28 & 39 & 48 & 50 \\ \cline{1-1}  & C10 & 24 & 75 & 39 & 73 & 14 & 28 & 27 & 40 & 6 & 17 & 11 & 17 & 28 & 82 & 49 & 85 \\ \cline{1-1} \cline{2-15}  & Mean & 27 & 52 & 49 & 56 & 16 & 26 & 28 & 37 & 8 & 16 & 12 & 16 & 32 & 60 & 58 & 69 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Orbit RMS [cm] comparison for four networks: Chinese regional network (CHN), Asian-Pacific network (AP), Asian network (ASIA), and global network (ALL). Figure 8: **(a)** 3D-RMS for GEOs of different networks. **(b)** 3D-RMS for IGSOs of different networks. different networks. From Figure 1, it is obvious that PETH and SIGP enhance the tracking geometry to IGSOs significantly. Although the two stations also observe all the GEOs from the elevations to GEOs in Table 7 the observations can hardly strengthen the constraint in along-track, as these two stations locate in the same narrow longitude zone of the CHN network. On the contrary, the ASIA network (adding DHAB to CHN network) extends the coverage of the CHN network to the west remarkably. Thus the 3D-RMS of GEOs drops from above 3.0 m to 1.3 m on average and IGSO orbits are also improved, but only slightly. Furthermore, from the RMS of each GEO satellite we notice that the 3D-RMS for C03 and C05 is reduced from several meters to decimeter-level, being very close to that of IGSOs, whereas very small changes for C01 and C04 are observed. If we examine the RMS in components, the improvement is taken place on the along-track direction. From the sky plot of DHAB in Figure 7 and the elevations in Table 7, C03 and C05 have a rather high elevation to DHAB while C01 and C04 are not visible because they are on the other (eastern) side and far away from DHAB. For the ALL network with all the tracking stations, the RMS of IGSOs are reduced on average by about 50% compared with the other three networks, for example, 3D-RMS drops from about 60 cm to 32 cm. Compared with CHN and AP, ALL brings a dramatic improvement for C03 and C05 in along-track direction as ASIA does. There are about 10% further improvements in GEOs orbits compared to the ASIA network.