## 4 Satellite Precision Orbit Determination and Accuracy Analysis
### Analysis of Orbit Accuracy  
The accuracy of orbit determination can be effectively reflected by reasonable validation of orbit determination results. The accuracy evaluation methods mainly include internal coincidence checking and external coincidence checking. In this section, the internal validations accuracy of the reduced-dynamic orbit is evaluated using the overlapping orbit validation, and the external accuracy is evaluated by the comparison with the CNES orbit, SLR validation, and SLR three-dimensional validation. These validation procedures collectively provide a comprehensive assessment of the accuracy and reliability of the orbit determination results. (1) Overlapping orbit validation  
Overlap orbit validation is performed to compare the results of two independent orbit determination, which can initially reflect the accuracy and stability of orbit determination. The data from one day are divided into two arcs for orbit determination, and the periods are 00:00-15:00 and 09:00-24:00, respectively. Because of the two independent orbit determination processes, the orbit determination results can be considered to be unrelated. At the same time, in order to avoid the boundary effect, the overlapping arcs from 10:00 to 1  
shows the radial, tangential and normal RMS values of the reduced-dynamic (RD) orbit of the HY-2B/2C/2D satellites compared with the CNES orbit. This comparison aids in assessing the consistency and accuracy of the precision orbit determination results. As can be seen from Figure 7 and Table 7, compared with the orbit provided by CNES, the reduced-dynamic orbits of HY-2B/2C/2D satellites have the best accuracy in the R direction, reaching 1.2 cm, 0.97 cm, and 1.32 cm, respectively, and the 3D RMS are 2.88 cm, 2.75 cm, and 2.85 cm, respectively. The fluctuation range of the RMS value in the R direction is 0.74-1.58 cm, in the T direction 1.67-2.81 cm, and in the N direction 1.03-2.25 cm, and the fluctuation range in the R direction is the smallest. The 3D accuracy of HY-2B/2C/2D satellites is less than 3 cm, which can fully meet the needs of high-precision satellite orbit determination. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**HY-2B**} & \multicolumn{3}{c}{**HY-2C**} & \multicolumn{3}{c}{**HY-2D**} \\ \cline{2-10}  & **R** & **T** & **N** & **R** & **T** & **N** & **R** & **T** & **N** \\ \hline Min & \(-3.06\) & \(-3.83\) & \(-3.48\) & \(-3.21\) & \(-4.01\) & \(-2.91\) & \(-3.57\) & \(-4.17\) & \(-3.68\) \\ Max & 3.21 & 4.35 & 3.47 & 3.03 & 3.97 & 3.67 & 3.25 & 3.35 & 3.36 \\ Mean & 0.23 & 0.11 & 0.05 & \(-0.07\) & \(-0.06\) & 0.13 & \(-0.13\) & \(-0.21\) & \(-0.03\) \\ STD & 1.17 & 2.18 & 1.31 & 0.97 & 2.08 & 1.40 & 1.31 & 2.02 & 1.40 \\ RMS & 1.20 & 2.26 & 1.31 & 0.97 & 2.08 & 1.41 & 1.32 & 2.07 & 1.40 \\
3D RMS & & 2.88 & & & 2.75 & & & 2.85 & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Statistics of intercomparison results between RD and CNES orbits (cm). Figure 7: Intercomparison between RD and CNES orbits in the R, T, and N directions. (3) SLR validation  
The SLR observation data for HY-2B/2C/2D satellites, made available by the International Laser Ranging Service Organization, was used to perform an external coincidence accuracy check of the orbit. This involved comparing the distances calculated from SLR data to the LEO with the distances obtained from the orbit determination results, and the difference between the two was statistically analyzed [40]. It is important to note that the accuracy of SLR station coordinates plays a significant role in the validation results [41]. The International Laser Ranging Service (ILRS) has published SLR2008 and SLRF2020, and the experiment reveals that the coordinates of SLR station are calculated using the two sources to have centimeter-level disagreements in the x and y directions, and millimeter-level disagreements in the z direction.