## 4 Validation and Discussion of Land Subsidence Results
### Typical Land Subsidence Areas Discussion
#### 4.3.1 Feature Point Deformation Analysis  
In order to better understand the spatiotemporal variation characteristics of the entire study area from 2016 to 2022, six feature points in large settlement areas were selected for the analysis of time series deformation, and the corresponding high-resolution optical image is described in Figure 11.  
Figure 9: The average annual displacement (**a**) and standard deviation for Sentinel-1A and TerraSAR data during the year 2020–2021 (**b**); the standard deviation of the annual mean deformation rate is respectively shown in (**c**,**d**) for Sentinel-1 and TerraSAR data. The red curves mark the fitted gaussian curves.  
Figure 11: The position and accumulation displacement of characteristic points (the position of points is shown in Figure 7). The graphs marked by (**A**)–(**F**) represent the deformation condition of PS01–PS06, the graphs marked by (**a**)–(**f**) is the corresponding optical images.  
Figure 10: (**a**) StaMPS annual average deformation rate; (**b**) the difference between annual deformation results obtained via StaMPS and SBAS-InSAR technologies.  
The position distribution of feature points is shown in Figure 7. In the coastal region, the PS01 characteristic point is located at BS District Five Mineral Flow Shanghai Co., Ltd., with a maximum settlement of \(-114.4\) mm. Furthermore, PS03 is located at PD International Airport, where the settlement construction is mainly on the newly built runway, and the average annual maximum deformation was \(-32.4\) mm/a, and the cumulative settlement was \(-92.5\) mm during the entire study period. In the main urban area of Shanghai city, the characteristic point PS02 is located on Zhangjiang Sanxiang Haishang, PD New Area, with a maximum annual average deformation rate of \(-26.5\) mm/a and a cumulative settlement of \(-100.8\) mm. PS04 is located near the Maqiao Center River and Jinguo Park in the MH District, with a maximum settlement accumulation of \(-81.9\) mm, and most of the settlement is linearly related to human activities. Point PS05 is located at the JS District Cultural and Creative Industry Park, where the surrounding area is mostly farmland, and the construction and development show an obvious linear settlement trend with the maximum cumulative settlement of \(-88.2\) mm. Point PS06 is located near the Xinghuo Development Zone and Songsheng Equestrian Club in the FX District, which is close to the sea, and the soil is rich in water and the soil layer spacing is large; therefore, the PS06 area is susceptible to subsidence.  
Figure 12 shows the cumulative ground elevation change in the selected feature points from 2016 to 2022, and the sedimentation trend increased year by year and shows a linear trend settlement. The settlement of coastal areas varies greatly compared with that of inland cities, while the coastal settlement of PS02 characteristic points is relatively stable compared with that of PS01 characteristic points. From 2016 to 2020, the overall subsidence underwent an obvious deformation, and the land subsidence remained basically stable after 2020.