## 3 Case Studies  
### Case Study in Hong Kong  
In Hong Kong, the Geodetic Survey Section of the Survey and Mapping Office (SMO) built the Hong Kong Satellite Positioning Reference Station Network (SatRef), which provides real-time network RTK and DGNSS correction data and GNSS raw data for users through 18 reference stations. The station information (receiver, antenna, and monument type) of SatRef is shown in Table 3. The authors of [46] suggested that users choose a reference station for forming a baseline within 20 km.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Site ID** & **Receiver** & **Antenna** & **Type of Monument** \\ \hline \hline HKKT & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, hilltop \\ \hline HKLT & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, hilltop \\ \hline HKMW & Trimble NetR9 & LEIAR25.R4 LEIT & Concrete block, hilltop \\ \hline HKNP & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, hilltop \\ \hline HKOH & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, hilltop \\ \hline \hline \end{tabular}
\end{table}
Table 3: Station information for the Hong Kong SatRef stations (stations are arranged by the type of monument).  
Data Description  
One of the multipath characteristics is that the pattern of the multipath repeats every satellite orbital cycle. Among the four GNSS systems, Galileo satellites have the longest satellite repeat period, excluding the abnormal cases of satellites E14 and E18 [47], which have a ten-day period. Therefore, a period of 10 days was selected as the observation period per month. Moreover, six months of data are used for the data quality assessment in order to cover all possible satellite-reflector-antenna geometries (i.e., different multipath errors) at a site.  
Considering the available SatRef GNSS raw data format and the support of each data format for the GNSS systems, RINEX 3.02 was chosen to obtain GPS, GLONASS, Galileo, and BDS signals. Moreover, the smallest available observation interval, 1 s, was chosen in order to better thoroughly investigate the multipath effect. The summary of the GNSS observation files is shown in Table 4.  
\begin{table}
\begin{tabular}{l l l l} \hline
**Site ID** & **Receiver** & **Antenna** & **Type of Monument** \\ \hline HKSL & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, \\  & & hilltop \\ \hline HKSS & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, \\  & & hilltop \\ \hline HKST & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, \\  & & hilltop \\ \hline HKWS & Leica GR50 & LEIAR25.R4 LEIT & Concrete block, \\  & & hilltop \\ \hline HKCL & Trimble NetR9 & TRM59800.00 SCIT & Concrete block on \\  & & building roof \\ \hline HKKS & Leica GR50 & TRM59800.00 SCIS & Concrete block on \\  & & building roof \\ \hline HKLM & Leica GR50 & TRM59800.00 SCIS & Concrete block on \\  & & building roof \\ \hline HKPC & Leica GR50 & LEIAR25.R4 LEIT & Concrete block on \\  & & building roof \\ \hline HKQT & Trimble NetR9 & TRM59800.00 SCIT & Concrete block on \\  & & building roof \\ \hline HKSC & Leica GR50 & LEIAR25.R4 LEIT & Concrete block on \\  & & building roof \\ \hline HKTK & Leica GR50 & TRM59800.00 SCIS & Concrete block on \\  & & building roof \\ \hline KYC1 & Trimble NetR9 & TRM57971.00 NONE & Concrete block on \\  & & building roof \\ \hline T430 & Leica GR50 & TRM59800.00 SCIT & Concrete block on \\  & & building roof \\ \hline \end{tabular}
\end{table}
Table 3: _Cont._Pseudorange multipath errors, carrier-phase multipath errors, and carrier-phase measurement noise of GPS, GLONASS, Galileo, and BDS measurements of the SatRef stations at a 95% confidence level are shown in Tables 11-13, respectively. The GPS, GLONASS, Galileo, and BDS data quality results per type of monument, receiver, and antenna are shown in Tables 14-15.