## 3 Study Area and Data Processing
### Data Processing  
To illustrate the reliability of the method in this paper for ground displacement monitoring, the paper uses the conventional time-series InSAR techniques (PS-InSAR technique  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Items** & **Description** \\ \hline Strip mode & IW \\ Orbital inclination & 98.18\({}^{\circ}\) \\ Waveband & C \\ Incidence angle & 33.88\({}^{\circ}\) \\ Orbital height & 693 km \\ Orbit direction & Ascending \\ Polarization & VV \\ Path & 40 \\ Frame & 112 \\ Resolution & Range 2.3 m/Azimuth 13.9 m \\ Time spans & 20 May 2017–17 December 2018 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Details of the processed SAR data.  
Figure 2: Locations of the study area.  
and SBAS-InSAR technique) and the method proposed in this paper to process the SAR images covering the study area. The data are processed mainly using GAMMA_2021 software for the interferogram generation, DSIpro_v2.0 software for the homogeneous selection and phase optimization, and StaMPS_4.1b1 software for the CPs selection and integration.  
Firstly, the GAMMA_2021 software was used to obtain the differential interferograms after the Sentinel 1A single look complex SAR images have been acquired, including data import, registration, and interferometry. During the PS-InSAR data processing, the SAR image of 28 March 2018 was selected as the master image and the other images as slave images while being aligned with the master image. The maximum value of the time baseline was 312 days. The longest spatial baseline was 120 m and the shortest was 9.5 m, generating a total of 24 pairs of interference pairs. The spatiotemporal baseline connection map is presented in Figure 3a. During the SBAS-InSAR data processing, the temporal baseline threshold was set to 80 d and the spatial baseline threshold was set to 80 m. Each image was limited to a maximum of 5 sets of interferograms with other images, resulting in the acquisition of 48 sets of differential interferometric pairs. The spatiotemporal baseline connection map is presented in Figure 3b. Based on this relationship, the coordinate transformation and resampling between the master and slave images were carried out to increase the registration precision to 1/8 pixels [28]. The precision orbital data provided by European Space Agency (ESA) was used for precise orbital estimation and flat earth effect removal in interference avoidance [29]. Additionally, the 30-resolution SRTM DEM data were used for geocoding and topographic phase compensation [30].  
Secondly, the StaMPS_4.1b1 software [31] was used to obtain to select PS points and SDF points from the single master and multi-reference interferograms, and the amplitude departure threshold was set to 0.4 and 0.6, respectively. Furthermore, the integrated PS/SBAS phases can be obtained by using the ps_sb_merge function after selection of PS and SDF points.  
Thirdly, the FaSHPS algorithm based on the SHP_selPoint function from DSIpro_v2.0 software [32,33] was used to select homogeneous points from the differential interferogram obtained based on a single master interferograms, and the significance level was 5% for a 11 \(\times\)11 experimental window. After homogeneous selection, the covariance matrix estimation algorithm based on the AdpCohEst function was used for homogeneous phase optimization and to obtain the phase-optimized differential interferograms, reducing phase noise and improving coherence values. Then, the DS points with good coherence and high SNR were selected after the phase-optimized differential interferograms were introduced into StaMPS_4.1b1 software. Afterwards the DS points and PS/SDF points were integrated in the same way as the integration of the PS points and SDF points.  
Figure 3: Spatial and temporal baselines of the interferometric pairs: (**a**) PS-InSAR and (**b**) SBAS-InSAR. The \(x\)-axis represents the temporal baseline, the \(y\)-axis represents the perpendicular baseline, black dots indicate SAR images, red dots indicate master SAR images and black lines denote interferograms.