## 2 Data Processing and Analysis Method
### GPS Data Acquisition and Processing  
Hong Kong is located on the north coast of the South China Sea, and is mainly composed of the Kowloon Peninsula and many islands. The Hong Kong coastline is complex and is affected by OTL GPS observation data for 2008-2017 provided by the Surveying and Mapping Office of the Hong Kong Lands Department ([[https://www.geodetic.gov.hk/smo/gsi/programs/tc/index.htm](https://www.geodetic.gov.hk/smo/gsi/programs/tc/index.htm)]([https://www.geodetic.gov.hk/smo/gsi/programs/tc/index.htm](https://www.geodetic.gov.hk/smo/gsi/programs/tc/index.htm))) were used, in which the HKFN station was replaced by the T430 station after 2014. The distribution of the GPS reference stations in the Hong Kong area are shown in Figure 1.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Harmonic Constituent** & **Period/h** \\ \hline M2 & Principal lunar semi-diurnal & 12.4206 \\ S2 & Principal solar semi-diurnal & 12.0000 \\ N2 & Larger lunar elliptic semi-diurnal & 12.6583 \\ K2 & Luni-solar declinational semi-diurnal & 11.9672 \\ K1 & Luni-solar declinational diurnal & 23.9345 \\ O1 & Principal lunar declinational diurnal & 25.8193 \\ P1 & Principal solar declinational diurnal & 24.0659 \\ Q1 & Lunar elliptic diurnal & 26.8680 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The periods of the eight semidiurnal and diurnal tidal constituents.  
Figure 1: Distribution of the GPS reference stations in the Hong Kong area.  
By using 24-h GPS observation data in RINEX format, the kinematic PPP solution for every 600 s was carried out with Bernese GNSS software version 5.2 [29] ([[http://www.bernese.unibe.ch/docs/DOCU52.pdf](http://www.bernese.unibe.ch/docs/DOCU52.pdf)]([http://www.bernese.unibe.ch/docs/DOCU52.pdf](http://www.bernese.unibe.ch/docs/DOCU52.pdf))), in which the elevation cutoff angle was set to 3\({}^{\circ}\). The main parameter files, i.e., satellite orbit, 30 s satellite clock, Earth rotation, ionosphere parameter, and differential code bias (DCB), were provided by the European Center for Orbit Determination in Europe (COD). The tropospheric delay was modeled using the Global Mapping Function (GMF) [30]. The antenna phase center file used PCV_COD.I08. Body tide and pole tide were modeled according to the IERS Convention 2010 [26]. No corrections were applied to the ocean and atmospheric tide loading.  
The estimated KPPP coordinates were in the IGS08 reference frame. The origin of IGS08 is defined as the center of mass (CM), including the solid Earth, the ocean, and the atmosphere, which is usually called the CM frame. Coordinates under IGS08 reference frame were transformed into the station coordinate system, including east, north, and vertical directions. The linear trend of the vertical series was removed. A threshold of 200 mm was set to eliminate gross errors. The % of Gross Errors are shown in Table 2. The eight semidiurnal and diurnal tidal components in the vertical direction at 12 stations were estimated using the method described in Section 2.1. The amplitudes and phases of OTL displacements for eight tidal constituents determined by GPS KPPP are listed in Tables 1 and 2.