# Study of Fast and Reliable Time Transfer Methods Using Low Earth Orbit Enhancement
## 3 Experimental Method  
### Data Source  
To investigate the impact of the GNSS PPP model with LEO-augmented GNSS time transfer performance, we used the GPS observation data provided by the IGS for day 1 in 2022 and the related precise products. A cohort of 13 stations was curated based on equipment type and geographic location. The station coordinates were fixed during PPP solving, and the station information is shown in Table 1 below.  
Utilizing the aforementioned stations, ten time transfer links were established. The time transfer link information is shown in Table 2, and the spatial distribution of the ten time transfer links is illustrated in Figure 1.  
With regard to the LEO satellite observation data, the ground station of the MGEX observation network was used to simulate the LEO satellite ground observation data based on the above LEO satellite observation simulation method. The daily average number of visible satellites in the LEO constellation on the first day of 2022 is shown in Figure 2. The relevant data used in the study are presented in Table 3.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Station** & **Latitude (\({}^{\circ}\))** & **Longitude (\({}^{\circ}\))** & **Elevation (m)** & **Clock Type** \\ \hline areg & \(-16.5\) & \(-71.5\) & \(2489.7\) & EXTERNAL RUBIDIUM \\ mcl & \(24.3\) & \(154.0\) & \(36.1\) & EXTERNAL RUBIDIUM \\ bor1 & \(52.3\) & \(17.1\) & \(125.3\) & EXTERNAL H-MASER \\ gold & \(35.4\) & \(-116.9\) & \(987.1\) & EXTERNAL H-MASER \\ ons1 & \(57.4\) & \(11.9\) & \(44.9\) & EXTERNAL H-MASER \\ pie1 & \(34.3\) & \(-108.1\) & \(2348.1\) & EXTERNAL H-MASER \\ usud & \(36.1\) & \(138.4\) & \(1509.0\) & EXTERNAL H-MASER \\ obi2 & \(-63.3\) & \(-57.9\) & \(33.1\) & EXTERNAL H-MASER \\ dif1 & \(52.0\) & \(4.4\) & \(76.3\) & EXTERNAL CESIUM \\ harb & \(-25.9\) & \(27.7\) & \(1558.5\) & EXTERNAL CESIUM \\ kiru & \(67.9\) & \(21.0\) & \(391.3\) & EXTERNAL CESIUM \\ sydn & \(-33.8\) & \(151.2\) & \(86.0\) & EXTERNAL CESIUM \\ syog & \(-69.0\) & \(39.6\) & \(50.1\) & EXTERNAL CESIUM \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of selected measurement station information.  
Figure 1: Global distribution of stations and time transfer links.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time Transfer Link** & **Distance (km)** & **Location** & **Clock Type** \\ \hline areg-mci & 11,858.8 & Low latitude & Rubidium clocks \\ gold-piel & 811.0 & Mid latitude & Hydrogen clock \\ pie1-ons1 & 7814.0 & Mid latitude & Hydrogen clock \\ onsl-bor1 & 658.2 & Mid latitude & Hydrogen clock \\ borl-usud & 8031.1 & Mid latitude & Hydrogen clock \\ kiru-dif1 & 1973.8 & Mid-to-high latitude & Cesium clock \\ dlf1-harb & 8205.9 & Mid–low latitude & Cesium clock \\ harb-ydn & 9763.0 & Mid–low latitude & Cesium clock \\ kiru-syog & 11,842.8 & High latitude & Cesium clock \\ ohi2-syog & 3908.6 & High latitude & Hydrogen–Cesium clock \\ \hline \hline \end{tabular}
\end{table}
Table 2: Time transfer link information.  
Figure 2: Average number of daily visible satellites of the LEO constellation on the first day of 2022.