## 1 Introduction  
Urban land subsidence is progressive or occurs due to a sudden decrease in the ground surface elevation due to the combined effects of natural factors and the impact of human activities [1, 2]. Natural factors include tectonic movement [3], earthquakes [4], volcanic activity [5, 6], and the natural consolidation of soil [7]. Human activity impacts mainly include the development of underground fluid resource extraction (groundwater, oil, natural gas, etc.) [8, 9], solid mineral exploitation [10], and pore soil compaction and consolidation settlement induced by engineering construction in soft oil areas [11]. Recently, many cities around the world have been affected by land subsidence disasters [12, 13, 14, 15, 16, 17, 18, 19, 20]. For example, the annual land subsidence in Mexico City is about 10 to 40 cm, causing buildings to tilt and crack [9], and the ground subsidence in Tokyo has adverse effects on the construction of underground engineering projects [16]. New Orleans and San Francisco in the United States, as well as areas such as Houston and Phoenix, have also experienced severe ground subsidence due to groundwater overexploitation [18]. In particular, the coastal plains and river deltaic regions experience a high rate of subsidence, and the destruction of waterproofing systems and sea level rises bring damage to basic living facilities such as buildings and subways [15; 20]. Thus, high-precision and long time series dynamic deformation monitoring is particularly important for areas with serious subsidence, and the governmental management departments should make timely decisions according to the disaster-related early warning information. At present, deformation monitoring methods include the global navigation satellite system (GNSS), leveling, three-dimensional (3D) laser scanning, and interferometry synthetic aperture radar (InSAR) technology [21; 22]. Compared with traditional measurement methods, InSAR has been a powerful monitoring method for research in many fields due to its advantages of being able to be used all day, having large-scale coverage, and having high precision [11; 23]. Among the multiple data processing methods, the small baseline subset (SBAS)-InSAR is widely used due to the increase in redundant observations of interference and the atmospheric effect reduction through spatiotemporal filtering [24]. By forming a combination of multiple small baselines with short baselines for time and space, SBAS-InSAR technology can improve the quality of interferograms to a certain extent, weaken the influence of speckle noise, and increase the utilization rate of effective data. Therefore, the SBAS-InSAR technology has been and will be considered to be the most promising deformation monitoring technology [25]. The land subsidence in Shanghai city has attracted the attention of many researchers, due to the continuous and serious deformation from a hundred years ago [26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42]. According to the annual subsidence rate of Shanghai, it experienced the following stages: developing (1921-1948); obviously developing (1949-1956); violently developing (1957-1961); slowing down (1962-1965); rebounding (1966-1971); and slowly developing (1990-2023). Researchers first discovered the land subsidence using the leveling measurement method in 1921 [26], and the subsidence became the most serious in the 1960s due to the excessive exploitation of groundwater resources. To effectively control the land subsidence disaster, Shanghai established a groundwater-level dynamic monitoring network and adopted measures such as reducing groundwater exploitation and the artificial recharge of groundwater. Generally, the subsidence intensity was alleviated from 1966 to 2000, with a cumulative average land subsidence of 218.1 mm and an average annual land subsidence of more than 6 mm.