## 2 Materials and Methods  
### Vertical Deformation from DInSAR  
The ground deformation can be obtained from the phase difference temporal SAR pairs. The basic concept is sending radar waves to the same position at different times and baselines. The phase differences of the two signals can be calculated with a reference digital elevation model. The control factors are accurate baseline and reflection on the ground surface. Moreover, precise orbit and reference DEM are also critical to finding actual deformation. DEM with 1 m resolution LiDAR DEM after the year 2009 is used as a reference in this study. The accuracy of ground deformation can be to less than a centimeter with the excellent quality of data, coherence, and amplitude. The phase difference of the interferogram cab is obtained by Equation (1). The actual ground deformation can be derived after removing known effects such as topography, geometry, and atmosphere. The atmosphere effect was eliminated by temporal scene filters without using any data from the meteorological station. Therefore, the interferometry can be calculated with a known baseline and reference height. The 1 m resolution LiDAR dem is adopted as reference height in this study. \[ \begin{array}{l}\emptyset_{Int}=4\pi\frac{R_{1}-R_{2}}{\lambda}=\phi_{Topography }+\phi_{Movement}+\phi_{Atmosphere}\\ =\frac{4\pi\frac{R_{1}}{\lambda R\sin\theta}\ln+\frac{4\pi}{\lambda}\Delta R_{ Movement}+\phi_{Atmosphere}}{\lambda R\sin\theta}\ln+\frac{4\pi}{\lambda}\Delta R_{Movement}+\phi_{Noise}\end{array}  \tag{1}\]  
in which R: distances between satellites and observation location; B: baseline; h: reference elevation; \(\lambda\): wavelength of the radar; \(\theta\): looking angle to the observation location. DInSAR, PS InSAR, and SBAS InSAR were developed very fast in recent years. These technologies are becoming more efficient for large-scale landslide monitoring. Various methodologies have been proposed for faster processing and better results [29; 30; 31; 32; 33; 34; 35; 36; 37; 38]. The reflection signal is feeble when a smaller wavelength sends it to the ground surface. This study uses single polarization (HH) for the same purpose a stronger reflection signal after testing in this area. The Sentinel-1 data was used for this research. The process to obtain DInSAR vertical displacement is shown in Figure 2 using only two temporal pairs and 1 m resolution LiDAR DEM to generate a simulated phase. The SAR processing software in this research is based on SARScape/ENVI. First, use the SAR images and DEM to produce coherence, interferometry, and simulated phase. After that, it eliminates layover and shadows from interferometry. However, the interferometry ranges from \(\pi\) to \(-\pi\) and the actual deformed phase is more than that. Thus, phase unwrapping is necessary for absolute phase differences. The final step is using GCP and precise orbit to convert the deformed phase to displacement. The DInSAR method is suitable to observe landslide scars at two scenes with a short baseline and short period. However, the coherence, amplitude, and fringes derived from two images are hard to continuously monitor for displacement. Thus, interferometric stacking is introduced for the study area. PSInSAR and SBAS are adopted in this area, but the PSInSAR result has much fewer candidate points. The number of candidate points extracted from PSInSAR is only 1/10 of SBAS. Thus, only SBAS is shown in this study. SBAS searches candidates with a similar radar signal amplitude by observing years and tracking their location in each scene. The atmosphere effect in this analysis is merely using temporal days and filters to eliminate. This study uses the European Space Agency (ESA) Sentinel-1 images due to its regular and 12 days return period. The temporal and space baseline is as shown in Figure 3. The temporal baseline is set to 60 days, and the space baseline is set to 150 m in this study. The images of ascending and descending used in this study are 126 and 121 images, respectively.