| In recent years,with the rapid development of China's economy,the process of urbanization continues to accelerate,but the surface subsidence in the city seriously restricts the pace of urban development,so it is urgent to carry out long-time series deformation monitoring of urban surface.The traditional monitoring methods are time-consuming and laborious,and the monitoring range is limited and inefficient,which can not meet the needs of urban surface monitoring at this stage.Because of its advantages of all-weather,wide coverage and high efficiency,InSAR technology has become one of the important methods of urban surface monitoring.With the further development of InSAR technology,radar differential interferometry(DInSAR)technology can effectively monitor the ground deformation information,but its defect is that it is difficult to solve the error effect caused by decoherence and atmospheric delay.SBAS InSAR and PS InSAR technology can overcome the above defects,so they are widely used in the fields of landslides,mining subsidence,urban ground and so on Settlement monitoring.Lanzhou,a typical Valley City on the Loess Plateau,is one of the major provincial capitals with frequent geological disasters due to its special terrain,high-rise buildings and the construction and operation of subway lines.Taking the main urban area of Lanzhou City as the research object and 45 sentinel-1a images from March2017 to November 2020 as the data source,this paper uses PS InSAR and SBAS InSAR methods to extract the average land deformation rate and cumulative land subsidence in the urban area,and makes an in-depth analysis of the causes of the subsidence.The main conclusions are as follows:(1)the subsidence of Lanzhou city is mainly distributed in the peripheral cities of the city The accumulated settlement of monitoring points in suburban area and urban area is small.This paper summarizes the basic principles of InSAR settlement monitoring,and focuses on the technical principles and characteristics of PS InSAR and SBAS InSAR.Based on sentinel-1a time series data,the deformation information of Lanzhou City from2017 to 2020 is extracted by PS and SBAS methods.The maximum cumulative settlement of Lanzhou City extracted by PS is 83.04 mm,and the maximum annual deformation rate is-24.12mm/year;the maximum cumulative settlement of Lanzhou City extracted by SBAS is 79.09 mm,and the maximum annual deformation rate is-22.64mm/year.Based on the accuracy verification of 8 sampling points with the same latitude and longitude,the differences between the two monitoring methods are further explored.According to the verification results,the two time series monitoring methods have high consistency from the location and range of settlement.(2)In order to further explore the relationship between the settlement point and various geographical factors,based on the settlement point information extracted by PS InSAR in the main urban area,six geographical factors,including stratum structure,stratum boundary,slope,aspect,elevation and river,and three human activity factors,including road construction,high-rise buildings,shantytowns and suburbs,were selected respectively to stack the settlement point and various factors for statistical analysis.It is found that in the stratigraphic structure,the main settlement points are distributed in the upper Pleistocene aeolian layer;from the perspective of the stratigraphic junction zone,the settlement points are mainly distributed in the range of 1000 m from the stratigraphic junction zone;when the slope is taken as the research object,the settlement points are mainly distributed in the range of 0 ? 16 ° slope;as for the surface elevation,the settlement points are mainly distributed in the range of 1557 ? 1878 m,with rivers as the research object The settlement points are mainly distributed in the range of 600 m on both sides of the river.In the interference of human activities,the settlement points are mainly distributed in the range of 300 m on both sides of the road by analyzing the urban roads;the settlement points are overlapped with the high-rise buildings in the urban area,accounting for 11.61% of the total settlement points in the study area;the settlement points are overlapped with the suburbs and villages around the city,accounting for43.15% of the total settlement points in Lanzhou.According to the extracted deformation information,Lanzhou city is mainly divided into seven settlement areas,of which the maximum cumulative settlement of xinghutai village is 67.38mm;the maximum cumulative settlement of the EMU parking station on the east side of dachaiping is42.52mm;the maximum cumulative settlement of the slope on the south side of Hualin mountain is 78.24mm;the maximum cumulative settlement of Heping Town in Yuzhong county is 78.41mm;the maximum cumulative settlement near Donggang is 77.46mm;the maximum cumulative settlement near Baigang is 77.46 mm The maximum cumulative settlement of Daoping village is 77.52 mm,and the maximum cumulative settlement near Lanzhou north station is 46.17 mm.Through further field investigation,it is found that these subsidence areas are mainly distributed in the suburbs of Lanzhou City and special terrain.(3)According to the extracted deformation information,it is found that the maximum cumulative settlement is 77.52 mm and the settlement rate is-22.65mm/year.Through Google Image and field investigation,it is found that the main reason of surface subsidence in these areas is human disturbance,such as high-rise building construction,old shantytown reconstruction and so on.(4)Through the spatial superposition of the monitored settlement points and the100 m buffer zone along the Lanzhou metro line,the statistical analysis shows that the settlement locations along the Lanzhou metro line are mainly located in some sections of Chengguan District,and the maximum cumulative settlement is mainly located in Wulipu station and Dongfanghong square station at the intersection of line 1 and line 2,with the maximum cumulative settlement reaching 66.76 mm. |
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