Research On Land Subsidence Monitoring In Lanzhou City Center Based On Sentinel-1 Data

Urban ground subsidence has the characteristics of slow development of ground deformation,irreversible,and difficult to monitor,but once the settlement is formed,it will cause hazards such as tilting and deformation of urban buildings and road surface collapse,which will not only cause serious losses to the economy of the entire city,but also It poses a serious threat to the lives of urban residents.Lanzhou City is located in the Loess Plateau in northwestern China.It is affected by various complex environmental factors such as loess subsidence,rainfall,and large-scale engineering construction.Various geological disasters occur frequently.Land subsidence is a typical representative of geological disasters in this area.Obtaining long-term sequence,strong vigour,and high-precision ground subsidence information is helpful to grasp the law of the slow change of urban ground disasters,so the dynamics of Lanzhou city in the time series Continuous ground subsidence monitoring has important practical significance.Interferometric Synthetic Aperture Radar(InSAR)technology,which has matured in recent decades,has brought new measurement methods to long-term surface deformation monitoring due to its wide coverage,short period,high accuracy,and all-weather monitoring..Persistent Scatterer Interferometric Synthetic Aperture Radar(PS-InSAR)technology widely used in ground settlement monitoring can not only monitor long-term series of surface deformation,but also monitor large areas,and its monitoring accuracy can reach millimeters level.In this paper,the Sentinel-1 TOPS image data of 70 scenes of orbit reduction is used as the data source.Based on the permanent scatterer interferometry(PS-InSAR),the surface deformation during the period from 2014.11 to 2019.10 in the downtown of Lanzhou was monitored,which further verified the Sentinel-1 The applicability of data in monitoring the surface deformation under the condition of loess.The main work done in this article is as follows:(1)Summarized the current status of domestic and foreign scholars using time series InSAR technology to monitor land subsidence,and discussed the feasibility of PS-InSAR technology,one of time series InSAR monitoring technology,to monitor urban land subsidence;(2)Analyze and summarize various sources of errors in InSAR data processing,explain the principle and processing flow of time-series InSAR technology in detail,and summarize the application of time-series InSAR technology in surface monitoring;(3)Taking the Lanzhou downtown area as the research area,the PS-InSAR technology was used to monitor the annual average deformation rate and cumulative settlement of the Lanzhou downtown area from 2014.11 to 2019.10.The monitoring results show that the Lanzhou downtown area is overall stable The settlement area mainly occurs in the streets and residential areas in the southeast direction of the city and the two mountains in the north and south of the city.The settlement in the southeast area has the characteristics of "band" distribution.The average annual maximum settlement rate during the monitoring period is-39.5mm/yr,and the cumulative maximum settlement It is-195.7mm,the settlement rate is mainly concentrated between-9.5mm/yr ~-4.1mm/yr,and the lifting rate is mainly concentrated between 3.1mm/yr~5.6mm/yr;(4)Select the ascending and descending orbit data in the same study area and the same time period,and use PS-InSAR technology to compare the annual average settlement rate and cumulative settlement amount monitoring results.The results show that the cumulative settlement curve of the ascending and descending orbit All of them can be well matched,which proves the accuracy and validity of the monitoring results;(5)The thesis discussed qualitatively the possible causes of ground subsidence.The ground settlement in the downtown area of Lanzhou from 2014.11 to 2019.10 may be related to the characteristics of long construction projects and loess collapsing.In order to explore the causes of settlement,the number of large-scale construction projects in the typical settlement area in the downtown area of Lanzhou was separately counted.In addition,the characteristics of the loess in the study area were analyzed.It can be found that during the monitoring period,the typical settlement area has been accompanied by Construction of large construction projects.The construction of large-scale engineering projects is accompanied by construction borrowing,land leveling,foundation tamping,and buried pipework for underground pipelines.At the end of these projects,the excavated ground may not be completely compacted during the earthwork backfill stage,thus affecting the rainwater.Underneath,the buildings above the loess foundation were subsidenced by the impact of the loess collapsing,which caused the entire ground to sink.The long-term serial monitoring results of the ground deformation in the downtown area of Lanzhou in this paper provide the region with strong ground subsidence data,including the identification of typical subsidence areas and the spatial and temporal changes of the subsidence area deformation,which can not only provide urban land planning It has a favorable scientific basis and has certain reference significance for the prevention and control of ground disasters.