Combining time series InSAR with GIS for assessing health condition of urban facilities: a case study of Hangzhou, China

Nearly all major Chinese cities have undergone dramatic modernization process featured by large scale construction of overpasses, skyscrapers and subway systems during last decade. As a result, ground displacements, e.g. ground subsidence have been reported in many occasions which causes cracks or even collapse of buildings, breakdown of underground pipelines, and water logging in urban areas. Therefore, accurate deformation information plays an important role in maintaining and assessing urban Geohealth. Interferometric Synthetic Aperture Radar (InSAR), especially time series InSAR represented by permanent scatterers InSAR and small-baseline subset (SBAS) techniques has become operational tools to map ground deformation over a large area. In this research, 41 Cosmo-SkyMed sequential SAR images in stripmap mode acquired between Jan. 2015 and Mar. 2018 were processed to generate ground deformation over Hangzhou , the capital city of Zhejiang province, China. Thanks to the high spatial resolution and high temporal frequency of the SAR stack, both the average deformation velocity and the time-series deformation over very dense coherent points were retrieved, which confirmed the advantage of InSAR in providing areal rather than point-like deformation measurements against leveling and GNSS techniques. By overlaying thematic GIS data on the deformation data, land patches with relatively large deformation velocity could be easily identified. Furthermore, through checking the land use types over these patches, the causes and risks of deformation were investigated in further analysis. On the other hand, the deformation over some important facilities, including the high-speed railway station, bridges and transportation networks were checked to diagnose the health conditions according to their subsidence evolution curve. This study demonstrates the potential of InSAR-derived deformation in assessing urban Geohealth condition.