Joint Analysis Of Multi-platform MT-InSAR Deformation Time Series Based On Stepwise Strategy

In order to ease the pressure of urban expansion and population growth,a large area of land had been reclaimed from beach wetlands along the eastern coast of Shanghai.Due to self-weight consolidation effect of dredger fill and the dynamic load caused by human activities,apparent ground deformation has occurred after completion of reclamation in this region.It has caused potential damage to buildings and infrastructures.Based on 35 ENVISAT/ASAR(ENV)images obtained from February 26,2007 to September 13,2010,61 Cosmo-SkyMed(CSK)images acquired from December 7,2013 to March 18,2016,and 31 Sentinel-1A(S1A)images collected from February 26,2015 to February 4,2017,Small Baseline Subset(SBAS)method was used to study the spatial-temporal distribution of ground deformation of Shanghai reclamation area in three different time periods,respectively.Then,three-dimensional ground deformation decomposition was performed by applying Minimum Acceleration(MinA)method based on CSK time series and S1 A time series in line of sight(LOS)direction.The purpose of 3D ground deformation decomposition is to understand whether the deformation component in horizontal direction is negligible or not in Shanghai reclamation area.According to the results of three-dimensional deformation decomposition,we transformed the LOS deformation measurement of each dataset to vertical direction by using the incidence angle of each satellite.Finally,the unique deformation time series in the study area spanning the time about 10 years was obtained by applying SVD method and geotechnical centrifuge model based on vertical deformation time series of each dataset.The measurements of three datasets retrieved by SBAS method show that obvious ground subsidence occurred from 2007 to 2010,2013 to 2016,and 2015 to 2017.The areas with obvious ground subsidence mainly include Pudong International Airport,Nanhui East Shoal,and the eastern part of Dishui Lake.The statistical analysis shows that the mean value of cumulative ground deformation in study area is about-37 mm from 2007 to 2010,according to the average value of annual ground deformation rate of about-11 mm/year.From 2013 to 2016,the mean cumulative ground deformation is about-12 mm,and the average annual ground deformation rate is about-5 mm / year.When it comes to 2015 to 2017,the two values are-11 mm and-5 mm/year respectively.The ground deformation process in the study area gradually decreased over time,indicating that the foundation of the study area has gradually been stable.The results of three-dimensional ground deformation decomposition analysis show that,from February 26,2015 to April 4,2016,the mean ground deformation rate in east-west direction of all highly coherent points in study area is about 0 mm/year,among which 90% of the points correspond to deformation rates of about-6 mm/year ~ 5 mm/year.For vertical direction,the mean ground deformation rate is about-4 mm/year,among which 90% of the points correspond to deformation rates of about-10 mm/year ~ 1 mm/year.We make the following conclusion: the value of ground deformation in horizontal direction of study area is obviously smaller than that in vertical direction.According to the results of three-dimensional deformation decomposition,we further studied the ground deformation of Shanghai Pudong airport.The results show that the ground deformation of Pudong airport is mainly concentrated in vertical direction and there is no obvious ground deformation signal in horizontal direction.In terms of ground deformation spatial distribution,the western region above the natural ground is relatively stable,while the eastern region which was reclaimed is with obvious ground subsidence in vertical direction,and the deformation rate is approximately-30 mm/year ~ 5 mm/year.In addition,the results of statistical analysis about the airport runways show that the deformation rate of each runway in the vertical direction is significantly greater than that of horizontal direction.In addition,the ground deformation corresponding to different runways show significant differences,that is mainly due to the differences in completion time of the reclamation projects and the construction time of the runways.By performing joint analysis of the vertical deformation time series of three datasets,we finally obtained the unique ground deformation time series of Shanghai reclamation area spanning the time from 2007 to 2017.The results show that the mean cumulative ground deformation of study area in recent ten years is about-49 mm,and the mean ground deformation rate is about-5 mm/year.Among highly coherent points,98% of the points correspond to the cumulative ground deformation of about-275 mm ~ 5 mm and the ground deformation rate of about-29 mm/year ~ 1 mm/year.In addition,by analyzing the deformation time series of highly coherent points in the study area,we found that the trends of deformation time series of these points have been gradually stable with time,and the corresponding ground deformation rates gradually decreased.