###### Abstract
Laboratory tests, based on the principles of the consolidation theory [21], were performed, taking into account dredger fill type (alluvial deposits thickness, soil composition, and water content) and other engineering parameters, which also predict that such a residual settlement will continue over future years, but with decreasing annual rates. Figure 1: Landsat 8 image collected on 3 August 2015, which shows the city of Shanghai and its reclaimed coastal areas (since the 1980s) in Nanhui New City. Ocean-reclaimed areas are represented in pink and the black line identifies the Dachang–Zhoupu fault. Within this framework, the well-established remote sensing technique, known as Differential Synthetic Aperture Radar (SAR) Interferometry (DInSAR) [22; 23; 24; 25], can play a strategic role in the detection and monitoring of ongoing surface deformation signals at a large spatial scale. Over the past fifteen years, several DInSAR techniques aimed at investigating the time evolution of ground displacements have been proposed [26; 27; 28; 29; 30; 31]. Two families of DInSAR methods broadly exist today, Persistent Scatterers (PS) [26; 27] and Small Baseline (SB) techniques [28; 29; 30]. A well-known approach belonging to the class of SB techniques is the Small BAseline Subset (SBAS) [28] algorithm. It relies on the least-squares (LS) inversion of a suitably selected sequence of small baseline (SB) interferograms through the singular value decomposition (SVD) method [32]. Over recent years, DInSAR techniques have been widely applied to monitor deformation phenomena caused by several natural and anthropogenic hazards, including landslides [33; 34], ground failures due to tunneling excavations [35; 36], and terrain consolidation and land-subsidence of river deltas [37; 38; 39]. In this work, we investigate the deformation phenomena that affect the coastal area of the Shanghai megacity. Our study is based on the application of the SBAS-DInSAR technique to two sets of SAR images, collected by the C-band ASAR/ENVISAT sensor, and by the X-band COSMO-SkyMed (CSK) SAR constellation sensors. The processed SAR data span the entire time interval between 26 February 2007 and 18 March 2016. Due to the lack of a systematic acquisition plan of SAR data over the investigated area, there is a significant temporal gap (of about three years) between the available ASAR/ENVISAT and CSK data frames. As a matter of fact, over the past few years, satellite radar platforms have not regularly imaged the southeastern sector of the Shanghai coastal area. As a consequence, present-day archives of SAR images are characterized by a reduced number of scenes with compatible acquisition geometries, and most of them only cover spotted areas of the entire Shanghai district. In addition, a few time gaps, among the different currently-available SAR datasets, are present. To overcome these fundamental limitations, and in order to retrieve a unique displacement time-series (from 2007 to 2016) through combination of available CSK and ASAR/ENVISAT datasets, we developed and applied a proper methodology. The adopted multi-platform combination technique relies on the underlying assumption that, over areas under reclamation, the observed deformations are mostly vertical; moreover, it exploits the knowledge of proper time-dependent geotechnical models [15; 19; 40; 41; 42; 43]. The achieved results are in general agreement with previous studies [43; 44], which reported that Lingang New City was characterized, from 2007 to 2010, by annual subsidence rates ranging between 12 and 18 mm/year. They also show that higher deformation rates are measured in regions that are more proximal to the southeastern coast, in correspondence with the reclamation project that was started later.