Abstract
In this work, we study ground deformation of ocean-reclaimed platforms as retrieved from interferometric synthetic aperture radar (InSAR) analyses. We investigate, in particular, the suitability and accuracy of some time-dependent models used to characterize and foresee the present and future evolution of ground deformation of the coastal lands. Previous investigations, carried out by the authors of this paper and other scholars, related to the zone of the ocean-reclaimed lands of Shanghai, have already shown that ocean-reclaimed lands are subject to subside (i.e., the ground is subject to settling down due to soil consolidation and compression), and the temporal evolution of that deformation follows a certain predictable model. Specifically, two time-gapped SAR datasets composed of the images collected by the ENVISAT ASAR (ENV) from 2007 to 2010 and the COSMO-SkyMed (CSK) sensors, available from 2013 to 2016, were used to generate long-term ground displacement time-series using a proper time-dependent geotechnical model. In this work, we use a third SAR data set consisting of Radarsat-2 (RST-2) acquisitions collected from 2012 to 2016 to further corroborate the validity of that model. As a result, we verified with the new RST-2 data, partially covering the gap between the ENV and CSK acquisitions, that the adopted model fits the data and that the model is suitable to perform future projections. Furthermore, we extended these analyses to the area of Pearl River Delta (PRD) and the city of Shenzhen, China. Our study aims to investigate the suitability of different time-dependent ground deformation models relying on the different geophysical conditions in the two areas of Shanghai and Shenzhen, China. To this aim, three sets of SAR data, collected by the ENV platform (from both ascending and descending orbits) and the Sentinel-1A (S1A) sensor (on ascending orbits), were used to obtain the ground displacement time-series of the Shenzhen city and its surrounding region. Multi-orbit InSAR data products were also combined to discriminate the up–down (subsidence) ground deformation time-series of the coherent points, which are then used to estimate the parameters of the models adopted to foresee the future evolution of the land-reclaimed ground consolidation procedure. The exploitation of the obtained geospatial data and products are helpful for the continuous monitoring of coastal environments and the evaluation of the socio-economical impacts of human activities and global climate change.
Highlights
Many coastal cities have implemented land reclamation projects, which can effectively provide feasible conditions for the development of coastal cities [1,2,3,4,5]
The results indicate that the geotechnical model used to characterize the deformation phenomena in the Shanghai area can be successfully used for describing the deformation of other reclaimed areas even though the sub-soil characteristics are not entirely homogenous in the two investigated areas of Shanghai and Shenzhen
The current ground deformation rates were compared with those predicted using sets of ENVISAT ASAR images collected more than ten years ago over the same area and already used in investigations performed by other scholars
Summary
Many coastal cities have implemented land reclamation projects, which can effectively provide feasible conditions for the development of coastal cities [1,2,3,4,5]. The availability of additional SAR data covering the time gap is beneficial to shed light on the correctness of the ENV+CSK ground deformation time-series obtained, and the usefulness of the applied geotechnical model, to foresee the evolution of the ground displacement in the future, constrained by the available InSAR data. We investigated the correctness of the geotechnical model used in Shanghai by comparing the combined ENV+CSK ground deformation time-series obtained using that model (see [23] for additional details) with those obtained by the independent set of RST-2 data. By using two sets of ascending/descending ENV SAR data acquired between 2007 and 2010, we obtained the ground deformation time-series of the vertical (Up–Down) ground deformations by the use of the multi-temporal InSAR minimum acceleration combination (MinA) [34] technique. The novel issues discussed in this paper concern: (i) the exploitation of InSAR data to constrain different ground deformation models, (ii) the cross-comparison and validation of the models used, (iii) the extension of the used models in another geographical area, and (iv) the characterization of the recent ground deformations of Shenzhen, China
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