## 3 Results
### Solution Availability  
Solution availability was defined as the ratio of epochs in which position solutions were successfully derived to the total number of epochs for which position solutions were obtained using the CODE products. The analysis included only epochs where both GNSS observations and the corresponding orbit and clock products (or corrections) were available, which allowed the computation of positions and enabled an objective comparison of the performance of different solutions. \begin{table}
\begin{tabular}{c c} \hline \hline
**Items** & **Models/Methods** \\ \hline Reference coordinates & daily IGS SINEX files \\ PCO and PCV for satellite antenna &igs20.atx for CNES and CODE solutions; for BRDM and \\ PCO and PCV for receiver antenna & HAS the products were referred to APC \\ Ionospheric delay & isg20.atx \\  & ionosphere-free linear combination \\  & a priori value: GPT3 (VMF3 for CODE solution) \\  & estimated: wet component \\  & mapping function: GPT3 (VMF3 for CODE solution) \\  & gradients: estimated \\ Solid tides, ocean loading, Shapiro effects, phase wind-up & IERS convention 2010 \\  & float \\ Receiver clock correction & estimated separately for each system \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._Table 4 presents the results of this analysis, including the average number of satellites used for each solution. For both the BRDM and CNES solutions, a 100% availability was achieved for the GPS and combined GPS+Galileo constellations, with an average of approximately 9 GPS satellites and approximately 15.5 satellites, respectively, for the combined systems. For Galileo-only solutions, the availability was slightly lower--99.8% for BRDM and 99.7% for CNES--with a slightly reduced number of satellites: 6.8 and 6.5 on average, respectively. This is due to the fact that fewer Galileo satellites were available in BRDM and CNES products; for CNES products, about 20-21 Galileo satellites were available. Different results were observed for the HAS products. For Galileo, solution availability reached 99.9% with about 6.9 satellites used, while for GPS it was significantly lower--only 74%, with an average of 5 satellites used. The HAS service is not yet fully operational and is primarily focused on the Galileo system, which may explain the lower availability and accuracy of the GPS-based solutions [44]. This is further illustrated in Figure 2, which shows the average availability of HAS orbit and clock corrections per satellite for both the Galileo and GPS constellations, averaged over the entire observation period. The dashed line marks the 90% availability threshold, highlighting that Galileo consistently exceeds this level with average availabilities of 95.49% for orbit corrections and 95.95% for clock corrections. In contrast, GPS average availabilities are much lower, at 67.11% for orbit and 67.64% for clock corrections. Notably, 10 GPS satellites show an availability below 50%, with 4 of them even below 20%--G07 (IIR-M), G13 (IIR), G15 (IIR-M), and G30 (IIF)--which negatively impacts the overall GPS performance in HAS products. While these satellites come from different blocks--IIR, IIR-M, and IIF--there is no clear dependency between satellite block type and correction availability. This indicates that other factors, such as satellite-specific conditions, operational status, or current HAS configuration, may be more influential in determining the performance of individual satellites. Combining GPS and Galileo for HAS products slightly reduced the overall solution availability to 99.1%, with an average of 10.6 satellites used. This is likely due to the lower accuracy of the HAS products for GPS satellites, negatively affecting the overall quality of position solutions. The highest number of satellites used was recorded for the CODE solution: 9.3 GPS satellites, 8.1 Galileo satellites, and 17.4 satellites for the combined GPS+Galileo constellation.