## 1 Introduction  
Taiwan is located at the boundary of two plates, where frequent earthquakes occur. The collision of plates also results in orogen, increasing the height of mountains. Due to the island being surrounded by different seawater temperatures, the extreme weather changes very fast and induces numerous typhoons and rainfall. For example, in 2009, the highest accumulated rainfall in one typhoon event was 3000 mm. The amount was about three fourths of the average annual rainfall. These massive rainfall events are why such a small island covers many potential sliding slopes. Landslide hazard mitigation is an essential issue in Taiwan. Central Geological Survey started to map the large-scale landslide (deep-seated landslide) scars from LiDAR DEM in the past ten years after typhoon Morakot in 2009. The mapped landslide scars can be downloaded from the open data of the government (Available online: [[https://data.gov.tw/en](https://data.gov.tw/en)]([https://data.gov.tw/en](https://data.gov.tw/en)) (accessed on 1 June 2021)). The existing scars imply what year those landslide events occurred but cannot indicate current conditions. The prominent scars weere downloaded and mapped in detail by this study are as shown in Figure 1. The deep-seated scar was mapped by the criteria that the area should be larger than 10 ha. Thus, detailed investigation and mapping are done by this research. There are several minor scars and cracks found during field investigation and LiDAR DEM mapping. The geological formation of the study area is slate, which varies with different sandstone content. The formation of slate is facing southeast ranging from 20 to 70 degrees, which may induce slow sliding due to gravity. The deformation speed of these scars is the first key issue to installing the monitoring system or engineering treatment. Figure 1: Mapped landslide scars from LiDAR in the study area and its location in Taiwan. Generally, PSInSAR was a method to derive large area deformation such as ground subsidence or fault deformation [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14] performed landslide velocity detection with PSInSAR and SBAS and concluded that PS can have more solved points than SBAS. However, [PERSON] etal. [15] did not provide accuracy verification with these methods. [PERSON] et al. [16] used TerraSAR-X SAR to detect landslide activity with PSInSAR and showed that it is possible to map active landslides. [PERSON] et al. [17] combined PSInSAR with the steepest slope velocity and its variance to refine the landslide susceptibility map. [PERSON] et al. [18] used ENVISAT and GNSS data to verify PSInSAR accuracy. [PERSON] et al. [19] adopted sensors on buildings and PSInSAR for building deformation and risk classification. The resolution of reference DEM is also an important issue when doing PSInSAR. [PERSON] et al. [20] used 1 m airborne LiDAR and 20 m DEM to compare the results of PSInSAR and showed that higher resolution DEM is more suitable for the derivation of ground movement. [PERSON] et al. [21] combined UAV and PSInSAR for higher resolution DEM for coastal displacement detection. The displacement detected in [PERSON] et al. [21] is about 1.92 m in 8 years. The interferometric staking is also called A-DInSAR in recent years, including PSInSAR, SBAS, and so on [22; 23]. In addition to the two methods mentioned above, another TCP-InSAR can perform continuous DInSAR analysis. TCP-InSAR uses a temporary coherence point selection technique and can estimate long-term surface deformation without performing a phase reduction procedure [24]. In addition, [PERSON] et al. [25] also improved the PS-InSAR with poor results in mountainous areas or non-artificial structures by using a new algorithm to get better quality candidate points. This algorithm is called SqueeSAR. [PERSON] et al. [26] and used inclinometer measurements for landslide kinematic modeling. The method projected the velocity to the steepest slope direction and compared Envisat and Cosmos Skymed with PSISAR. We tried to initiate this study with SBAS.