Research On Land Subsidence Monitoring In Beijing Based On Multiple InSAR Technologies

Land subsidence is a geological disaster caused by the combined effects of human and natural factors,resulting in slow subsidence of the ground.It has characteristics such as irreversibility,wide impact range,and high difficulty in prevention.Beijing is one of the areas with the most severe land subsidence in China.Land subsidence occurred in the 1960 s,and with the development of cities,the amount of land subsidence in the area is gradually increasing,which poses a potential threat to society and people’s production and life.Therefore,monitoring land subsidence in the Beijing area has important practical significance.Traditional monitoring methods are time-consuming and labor-intensive,and can only capture changes at monitoring points,which has limitations in current urban land subsidence monitoring.Synthetic aperture radar interferometry(InSAR),as a new microwave remote sensing technology for earth observation,has the characteristics of large range,high precision and all-weather,and can effectively monitor the spatio-temporal evolution of urban land subsidence.It is one of the important means for earth observation.In recent years,InSAR technology has played an important role in the monitoring of land subsidence,ground cracks,earthquakes,landslides,glaciers and other disasters.This paper takes Beijing Plain area as the research area,typical subsidence centers and subway lines in the research area as the research objects,and uses 25 C-band Sentinel-1A ascending rail images covering Beijing area from January 2020 to March 2022.Three technologies,D-InSAR,PS-InSAR and SBAS-InSAR,were used to carry out research,providing technical support and theoretical basis for land subsidence monitoring in this area.The main research contents and conclusions of this paper are as follows:(1)Seven Sentinel-1 ascending orbit images were used to obtain the subsidence distribution of Chaoyang District of Beijing in four time periods from 2020 to 2022 based on differential interferometry(D-InSAR)technology.The results show that as the time baseline becomes longer,subsidence centers gradually form in the eastern and western parts of Chaoyang District,and the subsidence in the eastern part is more serious than that in the western part.The maximum cumulative shape variable reached-60 mm.(2)Two temporal InSAR techniques,PS InSAR and SBAS InSAR,were used to obtain the surface deformation rate field in the plain area of Beijing from 2020 to 2022.The results show that the surface deformation in the southwest of the study area is relatively stable,and the subsidence in the main urban area is small.A large area of subsidence area has been formed from the northwest of Haidian District and the southeast of Changping District to the east of Chaoyang District,the west and north of Tongzhou District,and the subsidence has a tendency to develop to Daxing District,The settlement in Chaoyang District and Tongzhou District is the most severe,with the maximum deformation rate reaching-60mm/yr and the maximum cumulative deformation exceeding-100mm;We also conducted deformation analysis along multiple subway lines in the study area,and the results showed that during the monitoring period,the subway network in the central and western regions was relatively stable,while the eastern section had regional settlement with a large settlement rate,and the maximum cumulative deformation variable along the line exceeded-70 mm.(3)Internal coincidence and external coincidence accuracy were verified for the surface deformation rate results obtained by InSAR technology.The results of internal coincidence accuracy showed that the absolute value of the deformation rate difference of more than 90%of the common pixels was less than 10mm/yr,indicating good internal accuracy.The results of external coincidence accuracy verification show that the monitoring results of PS-InSAR technology are better than those of SBAS-InSAR technology,and the reliability of InSAR monitoring results is proved by the results of internal and external coincidence accuracy verification.(4)The subsidence phenomenon of Beijing Plain was analyzed based on the results of surface deformation rate,fracture distribution and population distribution in the study area.The results show that geological structure and stratigraphic lithology are the internal conditions and overall factors for the formation of land subsidence in Beijing Plain.Local ground load,overconcentration of population and groundwater change are the external conditions and controllable factors for the development of land subsidence.In the future,the ground subsidence in this region can be prevented and controlled from these aspects.