## 2 Data and Theory Description
### The CPRAP Usage Data Description
#### 2.1.1 GNSS and RS PWV Data  
GNSS observations are derived from the Crustal Movement Observation Network of China (CMONOC), and the CMONOC was built starting 1997 and operated in 2001. CMONOC consists of more than 260 continuous operated GNSS stations and 2000 discontinuous regional observation stations [22]. In this paper, the corresponding observations of 260 continuous GNSS stations were selected over the period of 2012 to 2020 in China. GNSS observations are processed by the precise point positioning (PPP) technique and the specific processing procedures can be referred to our previous work [23]. Finally, the hourly ZTD was estimated at those selected stations. Due to lack of meteorological sensors at GNSS stations, use the temperature (T) and pressure (P) data provided by ERA5 the vertical interpolation of T and P data of ERA5 performed before bilinear interpolation [24].  
Integrated Global Radiosonde Archive (IGRA) includes more than 2000 stations all over the world [20] and the RS balloon are launched twice (UTC 00:00 and 12:00) or four times (UTC 00:00, 06:00, 12:00 and 18:00) a day [25]. The corresponding meteorological parameters, such as T, P and relative humidity, can be observed at different heights from the surface to the height of approximately 30 km [26]. In this study, the data of 87 RS stations were selected over the period of 2012 to 2020 in China. Figure 2 gives the geographical distributions of the selected GNSS and RS stations in China.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Category** & **Resource** & **Period** & **Spatial-Temporal Resolution** & **Source** \\ \hline \multirow{4}{*}{Ground-Based} & GNSS & 1 January 2012-31 December 2020 & 1 h & Station (260) & [[ftp://ftp.cgsp.ac.cn/products/](ftp://ftp.cgsp.ac.cn/products/)]([ftp://ftp.cgsp.ac.cn/products/](ftp://ftp.cgsp.ac.cn/products/)) (accessed on 24 April 2022) \\  & RS & 1 January 2012-31 December 2020 & 12 h & Station (87) & [[ftp://ftp.ncdc.noaa.gov/](ftp://ftp.ncdc.noaa.gov/)]([ftp://ftp.ncdc.noaa.gov/](ftp://ftp.ncdc.noaa.gov/)) (accessed on 24 April 2022) \\ \multirow{4}{*}{\
\begin{tabular}{c} Reanalysis- \\ Based \\ \end{tabular} } & ERA5 & 1 January 2012-31 December 2020 & 1 h & 0.25\({}^{\circ}\)\(\times\) 0.25\({}^{\circ}\) & [[https://www.www.fnf](https://www.www.fnf)]([https://www.www.fnf](https://www.www.fnf)). (accessed on 24 April 2022) \\  & FY-3A/MERSI & 1 January 2012-31 December 2013 & 5 min & 1 km \(\times\) 1 km & [[http://satellite.nsmc.org.cn/](http://satellite.nsmc.org.cn/)]([http://satellite.nsmc.org.cn/](http://satellite.nsmc.org.cn/)) (accessed on 24 April 2022) \\ \multirow{4}{*}{
\begin{tabular}{c} Space-Based \\ 3A/OLCI \\ \end{tabular} } & Sentinel- & 1 March 2019–4 March 2020 & 5 min & 0.3 km \(\times\) 0.3 km & [[https://schiub.copernicus.eu/](https://schiub.copernicus.eu/)]([https://schiub.copernicus.eu/](https://schiub.copernicus.eu/)) (accessed on 24 April 2022) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specific information of the data used for the establishing CPRAP.  
Figure 2: Geographic distributions of GNSS and RS stations selected in China.