## 4 Test Results
### Near-Real-Time LEO Satellite Clocks
As presented in Figure 7, it is noticeable that the trend of the clock errors is highly consistent for different \(\Delta T\). As \(\Delta T\) increases, the STDs of the clock errors are slightly improved. Table 3 lists the daily precision of the connected near-real-time clocks for different \(\Delta T\). From Table 3, it can first be observed that the connected near-real-time clocks over \(\Delta T\) based on 6 h Kalman-filter-based processing exhibit very similar precision to the daily kinematic clocks using the same CNES real-time products, i.e., with STD of the differences at 0.01 to 0.03 ns. Secondly, compared with the clocks determined by reduced-dynamic with CODE final products serving as the \"true\" clocks in this study, the STD of connected near-real-time clocks is about 0.2 to 0.3 ns. Having a look at the last column of Table 3, increasing the \(\Delta T\) can slightly improve the connected near-real-time clock precision, i.e., with an improvement within 0.02 ns when increasing \(\Delta T\) from 30 to 300 s. To reduce the required prediction period for real-time applications, a short \(\Delta T\) of 1 to 2 min should be a good choice. Figure 6: Comparison between the connected near-real-time Sentinel-3B clocks at the last \(\Delta T\) period over each processing arc, and different daily solutions, (**a**): \(\Delta T\) is 60 s; (**b**): \(\Delta T\) is 120 s; (**c**): \(\Delta T\) is 180 s; (**d**): \(\Delta T\) is 240 s; (**e**): \(\Delta T\) is 300 s. (K denotes the daily clock solutions using the Kalman-filter-based kinematic model with the CNES real-time products, RD denotes the daily clock solutions using the reduced-dynamic model with the CODE final products). Figure 8 shows the Modified Allan Deviations (MDEVs) [41] of the connected near-real-time clock errors using different \(\Delta T\). As shown in Figure 8, when the averaging time \(\tau\) is between the range of [100, 300], MDEV decreases with increasing \(\Delta T\). This corresponds to the conclusions from Table 3, i.e., a large \(\Delta T\) is beneficial for the continuity of the clock solutions, especially over the short term, due to fewer connections of the results. For a \(\Delta T\) of 300 s, the MDEV is slightly increased due to the disturbance of gross errors, which is consistent with its slightly larger STD as shown in Figure 7. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**DOY** & **STD (K vs. R) (ns)** & \(\Delta T\) (s) & **STD (vs. K) (ns)** & **STD (vs. R) (ns)** \\ \hline  & & & 60 & 0.025 & 0.218 \\ \cline{3-5}  & & & 120 & 0.021 & 0.218 \\ \cline{3-5}
227 & 0.211 & 180 & 0.018 & 0.218 \\ \cline{3-5}  & & & 240 & 0.015 & 0.215 \\ \cline{3-5}  & & & 300 & 0.015 & 0.201 \\ \hline  & & & 60 & 0.025 & 0.304 \\ \cline{3-5}  & & & 120 & 0.021 & 0.300 \\ \cline{3-5}
228 & 0.297 & 180 & 0.018 & 0.300 \\ \cline{3-5}  & & & 240 & 0.014 & 0.299 \\ \cline{3-5}  & & & 300 & 0.025 & 0.301 \\ \hline  & & & 60 & 0.028 & 0.246 \\ \cline{3-5}  & & & 120 & 0.024 & 0.245 \\ \cline{3-5}
229 & 0.237 & 180 & 0.020 & 0.245 \\ \cline{3-5}  & & & 240 & 0.017 & 0.241 \\ \cline{3-5}  & & & 300 & 0.028 & 0.230 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Daily STDs between the connected near-real-time clocks for different \(\Delta T\) and different daily clocks (K denotes Kalman-filter-based daily kinematic clocks using the CNES real-time products, R denotes the batch least-squares reduced-dynamic daily clocks using the CODE final products). Figure 7: The errors between the connected near-real-time Sentinel-3B clocks at the last \(\Delta T\) period for each processing arc, and the daily clock solutions using the reduced-dynamic model with the CODE final products to determine the LEO satellite clocks.