Analysis Of Land Subsidence In Shanghai Based On Multi-sensor Time-series InSAR Technolog

In the 1990 s,as Shanghai began to implement market economy reforms,the city ushered in a new round of development opportunities,with a large influx of people and large-scale urbanisation,and a new growth of land subsidence in the central city.Traditional techniques for measuring land subsidence have low spatial and temporal resolution and high economic costs,making it difficult to meet the requirements of monitoring large areas and long periods of time.The time series In SAR technique uses long time series of SAR satellite images for analysis,providing a high temporal and spatial resolution,high accuracy and low cost monitoring tool for land subsidence inversion.The SBAS-InSAR technique was used in this study.By using images from ERS-1/2,Envisat ASAR and Sentinel-1A,we carried out quantitative inversion of three periods of land subsidence in central Shanghai from 1992-2000,2003-2010 and 2015-2020.Then,data related to land subsidence such as groundwater,local climate zone classification,metro and population are obtained for the three periods.Unlike previous Shanghai subsidence studies.This study uses multi-sensor SAR satellite imagery to monitor land subsidence in Shanghai over a long time series.A local climatic zone classification system is used to investigate the influence of urban threedimensional structure on subsidence.Finally,a single factor and two-factor interactive quantitative analysis of subsidence was performed using geodetector method.These findings indicate that using InSAR technology to monitor subsidence in Shanghai,and to investigate multiple factors influencing subsidence,has great practical significance.(1)Time series InSAR land subsidence inversion.First,30 view ERS-1/2 data were used to invert land subsidence in central Shanghai from 1992 to 2000,with subsidence rates ranging from-47.55 to 27.05 mm/yr.The main subsidence funnels were located on both sides of the river in Huangpu District and in the core areas of Jing’an,Hongkou,Yangpu and Lujiazui bordering northern Huangpu.There are also significant subsidence vents on both sides of the river in Gongqing Forest Park,and in Changning and Putuo districts near Hongqiao Airport.Second,based on Envisat ASAR data,land subsidence for central Shanghai from 2003-2010 was estimated at-20.16-36.62 mm/yr.During this period,the total subsidence decreased and the three major subsidence areas which appeared in the 1990 s gradually expanded.Wusong Street and Songnan Town in Baoshan District saw the emergence of new subsidence funnels.In Pudong New Area,new subsidence funnels appeared in the area connected to Gaoxing Town and Gaodong Town in the north,and in the area connected to Shanggang Xincun subdistrict,Zhoujiadu subdistrict and Sanlin Town in the south.Finally,land subsidence in central Shanghai for 2015-2020 was inferred using 33-view Sentinel-1A data,with subsidence rate ranging from-18 to 8.74 mm/yr.During this period,the subsidence area shifted from the central core to the periphery of the study area,the subsidence magnitude further decreased,and the subsidence area became finer.(2)Comparative validation of subsidence results.To check the accuracy of the inversion results,it is necessary to compare the time-series In SAR results with the measured data for verification.The cumulative ground settlement map of the central city area was compared with the four phases published by the Shanghai Geological Data Information Sharing Platform.Data from two extensometer monitoring sites in the core area of Shanghai were also compared with the In SAR results.The results of the ERS-1/2 inversions were found to be consistent with the cumulative subsidence trends for the two periods 1991-1995 and 1996-2000,and the ENVISAT ASAR data inversions were generally consistent with the cumulative subsidence trends for the two periods 2001-2005 and 2006-2010.The measured data from the Extensormeter monitoring sites were then compared with the InSAR results from the same sites,and the two types of data maintained an extremely strong linear correlation.(3)Quantitative analysis of land subsidence and influencing factors.A geodetector tool was used to study in depth the mechanism of land subsidence in the central city of Shanghai.Groundwater level data,local climate zone classification data,metro data and population data for the three phases were obtained by various means.The above data were used as dependent variables,and the rate of land subsidence was used as the independent variable.After using the geodetector,the following conclusions were drawn.One is that the strength of the explanatory power of each individual factor on land subsidence is: groundwater > metro > local climate zone >population.The other is that the explanatory power of land subsidence is stronger after the two-factor interaction.The interaction between groundwater level and metro,with a q-value of 0.3018,has the strongest explanatory power for land subsidence.