## 4 Test Results
### Near-Real-Time LEO Satellite Clocks  
Using the CNES real-time GNSS satellite orbital and clock products, with the processing arc length \(T_{obs}\) set to 6 h, and the time interval \(\Delta T\) between subsequent processing sessions tested for 60, 120, 180, 240, and 300 s as explained in Section 3, near-real-time Sentinel-3B satellite clocks are determined. The blue lines in Figure 6 connect the near-real-time Sentinel-3B satellite clocks during the last \(\Delta T\) period over each processing arc, i.e., the most recently updated near-real-time satellite clocks to be used for prediction. The Kalman-filter-based daily clocks based on the kinematic model utilizing the real-time products provided by the CNES (red line), and the daily clocks based on the batch least-squares reduced-dynamic model using the CODE final products (yellow line) are given for comparison. The LEO satellite clocks are re-referenced to the same time reference, i.e., that of the CODE final clocks, for a fair comparison with:  
\[\Delta t_{p}^{ref}=\sum_{s=1}^{m_{p}}\frac{\left(t_{p}^{s_{1}}-t_{p}^{s_{2}} \right)}{m_{p}} \tag{10}\]  
\[\Delta\
abla t_{p}^{s,leo}=t_{p}^{s,leo}-t_{0p}^{s,leo}-t_{p}^{ref} \tag{11}\]  
where \(\Delta t_{p}^{ref}\) is the epoch mean difference between the real-time and the CODE final GPS clocks at epoch \(p\), and \(m_{p}\) is the number of the compared GPS satellites at epoch \(p\). \(t_{p}^{s_{1}}\) and \(t_{p}^{s_{2}}\) are satellite clock biases from the real-time and the CODE final products at epoch \(p\), respectively, and \(t_{p}^{s,leo}\) and \(t_{0p}^{s,leo}\) are the LEO satellite clocks determined based on real-time and the CODE final products at epoch \(p\), respectively. \(\Delta\
abla t_{p}^{s}\) represents the re-referenced clock difference at epoch \(p\). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Parameters** & **Processing Strategies** \\ \hline \multirow{8}{*}{Near-real-time clock determination} & \multirow{2}{*}{Observations} & Undifferenced IF code and carrier phase combination (GPS: L1/L2) \\ \cline{2-3}  & Sampling & 30 s \\ \cline{2-3}  & Elevation cut-off angle & 3\({}^{\circ}\) \\ \cline{2-3}  & GNSS orbits and clocks & Selected (Section 2.1) \\ \cline{2-3}  & GNSS satellite antenna PCO/PCVs & igs20.atx \\ \cline{2-3}  & LEO satellite antenna PCO/PCVs & Operator supplied \\ \cline{2-3}  & Phase wind-up & Corrected \\ \cline{2-3}  & Estimator & Kalman filter, Kinematic \\ \cline{2-3}  & \(T_{obs}\) & 6 h \\ \hline Clock Prediction & \(T_{pre}\) & Longer than \(T_{process}+\Delta T\) \\ \hline \multirow{2}{*}{Broadcast interval} & \multirow{2}{*}{Optional} \\ \cline{2-3}  & & \\ \end{tabular}
\end{table} 
Table 2: Processing strategy. As depicted in Figure 6, the trends of the connected near-real-time Sentinel-3B satellite clocks determined during the last \(\Delta T\) period of different arcs are generally consistent with the two types of daily solutions. Compared to the daily solutions based on the Kalman-filter-based kinematic model using the CNES products (yellow), the connected near-real-time Sentinel-3B clocks (blue) have fewer outliers. When using the 6 h arcs, the near-real-time clocks determined during the last \(\Delta T\) period are fully converged. The connected clocks determined from the different sessions do not exhibit obvious jumps at boundaries either, since \(\Delta T\) is much shorter than the processing arc length of 6 h, and shifting the observation arc by \(\Delta T\) each time does not lead to significant solution differences at the ending period of the processing arc. Figure 7 shows the differences between the connected near-real-time Sentinel-3B clocks (blue lines in Figure 6) and the daily clock solutions using the reduced-dynamic model with the CODE final products (yellow lines in Figure 6) over the test period. The results are shifted by \(N=(\Delta T/60-1)\times 2\) ns for each shifted \(\Delta T\) for a better demonstration.