| Land subsidence will damage urban construction and threaten people’s life safety.Therefore,it is of great significance to monitor urban surface deformation.PS-InSAR and SBAS-InSAR technologies use different models and methods to eliminate the residual phase of coherent points in the target area.Therefore,improving the efficiency and accuracy of the two technologies for topographic deformation monitoring is one of the urgent research topics.In this paper,two sequential InSAR techniques are used to monitor the surface deformation in Wuxi and Shanghai,and the causes of the deformation are analyzed;Taking Shanghai as an example,the risk of land subsidence is evaluated.The main research contents are as follows:1)Based on sentinel-1A data,the surface deformation information of Wuxi central urban area is retrieved by PS InSAR technology and SBAS insar technology integrating PS high coherence points.In order to study the monitoring effect of different monitoring methods on cities,and according to the different backscattering ability of different surface coverings to radar waves,this paper first takes Wuxi City as the research area,through a large number of experimental comparative analysis,takes the most appropriate parameters and uses two methods for inversion.The results show that the central urban area of Wuxi presents the characteristics of "uplift in the northwest and settlement in the South".The deformation rate range during the monitoring period is-14 ～ 20mm/a.The temporal and spatial distribution characteristics of typical deformation areas are analyzed.The experimental results of the two methods are compared and verified to be highly consistent,which verifies the feasibility of SBAS technology and is suitable for urban deformation monitoring.2)Using 42 images from May 2016 to August 2021 and the improved SBAS-InSAR technology,the surface deformation information of Shanghai is obtained,and the reliability of the results is verified with the leveling data.Since it is better to select high coherence control points for inversion during track refining with small baseline set,the improved SBAS-InSAR technology is used to monitor land subsidence in Shanghai.The results show that the overall surface deformation in Shanghai is relatively stable,some parts of the West are lifted,and the subsidence in the coastal area is more serious.Combined with geological structure,hydrological conditions,groundwater exploitation,rainfall and engineering construction factors,conduct quantitative analysis of temporal and spatial characteristics to understand the correlation between deformation inducement and settlement law.It provides a scientific reference for the prevention and control of land subsidence disasters in Shanghai in the future,which is conducive to the construction of ecological civilization and sustainable economic development.3)Based on the inversion results of land subsidence in Shanghai and the local actual situation,11 evaluation indexes are selected to construct the evaluation element set,the characteristics of each index sample are analyzed from the risk and vulnerability of land subsidence,the entropy weight method is used to determine the factor weight,and the risk evaluation model is established to obtain the evaluation results of land subsidence risk,vulnerability and risk in Shanghai,Spatial differentiation analysis: in the central urban area of Shanghai,the high-risk areas of land subsidence include Huangpu District,Hongkou District,Jing’an District,Putuo District and Changning District,as well as the area near the Huangpu River in Pudong New Area.The higher area is the area around the central urban area,the suburban area is generally the middle area of land subsidence,and Qingpu District and Songjiang District are in the low or low subsidence risk area.The results have reference and guiding significance in the prevention and monitoring of geological disasters in Shanghai. |
