## 5 Conclusions  
This paper systematically discusses the impact of an attitude model, PWU and PCV on the precise orbit and clock offset of GRCC and CS01 satellites, as well as the GPS data quality. First, we studied the space-borne GPS data quality of GRCC and CS01 from the performance of tracking GPS satellites, multipath errors and SNR variation. The overall data quality of GRCC is superior to that of CS01 because of manufacturing characteristics \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Spacecraft**} & \multirow{2}{*}{**Solutions**} & \multirow{2}{*}{**Residual**} & \multicolumn{6}{c}{**Overlap Comparison (cm)**} & \multicolumn{6}{c}{**JPL Comparison (cm)**} \\ \cline{3-10}  & & & **R** & **T** & **N** & **3D** & **R** & **T** & **N** & **3D** \\ \hline \multirow{3}{*}{GRCC} & without PCV & 7.81 & 0.73 & 1.52 & 1.24 & 2.11 & 1.89 & 1.91 & 1.23 & 2.98 \\  & with PCV & 7.31 & 0.72 & 1.50 & 1.23 & 2.08 & 1.78 & 1.63 & 1.29 & 2.75 \\ \multirow{3}{*}{CS01} & without PCV & 9.31 & 0.71 & 1.39 & 0.98 & 1.88 & / & / & / & / \\  & with PCV & 8.55 & 0.65 & 1.28 & 0.95 & 1.72 & / & / & / & / \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The RMS of residual and orbital comparison with/without PCV for GRCC and CS01. Figure 11: RMS of orbital differences for GRCC and CS01 with/without PCV corrections. Figure 12: The difference in clock offset between solutions with and without PCV corrections. and cost. The precise orbit and clock offset play a very important role in the LEO-based navigation enhancement system and the errors of the attitude model, PWU and PCV cannot be neglected. After correcting the errors of the attitude model, PWU and PCV, the orbit quality was further improved, as evidenced by residual analysis and overlap comparison. The final GRCC and CS01 orbit consistency (3D RMS) can reach up to 2.08 cm and 1.72 cm, respectively, which satisfies the high-precision requirement of LEO-based navigation enhancement systems. The impact of the attitude model, PWU and PCV on the clock offset of GRCC is 0.023 ns, 0.047 ns and 0.043 ns, and the impact of PWU and PCV on the clock offset of CS01 is 0.052 ns and 0.027 ns, respectively. For LEO-based navigation enhancement systems, the orbit and clock offset determine the overall performance. Small errors in the attitude model, PWU and PCV can also have nonnegligible effects on LEO orbit and clock offset. Therefore, the clock offset of LEO satellites should be given great attention in LEO-based navigation systems, not considered simple estimated parameters. Furthermore, this paper also shows that there is still room for improvement for LEO orbit and clock offset if we can process the attitude model, PWU and PCV carefully. Meanwhile, the orbit determination capability of our SHAOOD software was explored, and it can achieve centimeter level orbit determination accuracy. The research results of this paper can provide a reference for the construction of an LEO-based satellite navigation system. [PERSON] wrote the article and processed the data, [PERSON] designed the experiments, [PERSON] provided original data and suggestions, [PERSON], [PERSON], [PERSON] and [PERSON] contributed to discussions and revisions. All authors have read and agreed to the published version of the manuscript. This research received no external funding. All GRACE-FO data in this paper can be freely accessed at [[ftp://isdcftp.gtz-potsdam.de/grace-fo/](ftp://isdcftp.gtz-potsdam.de/grace-fo/)]([ftp://isdcftp.gtz-potsdam.de/grace-fo/](ftp://isdcftp.gtz-potsdam.de/grace-fo/)) (accessed on 11 March 2021). The GPS ephemeris and clock products can be found at [[ftp://ftp.aiub.unibe.ch/CODE/](ftp://ftp.aiub.unibe.ch/CODE/)]([ftp://ftp.aiub.unibe.ch/CODE/](ftp://ftp.aiub.unibe.ch/CODE/)) (accessed on 11 March 2021).