| Urban land subsidence is a kind of local engineering geological disaster that the ground elevation slowly decreaes due to the consolidation and compression of loose soil under the comprehensive action of human factors and natural factors.Urban land subsidence has the characteristics of irreversibility,wide influence range and difficulty in prevention.Since the 1960 s,the Beijing found serious land subsidence,with the rapid development of the Beijing urban construction,groundwater overexploitation and urban construction overload,making the land subsidence on the basis of original steady accumulation,causing the loss of urban flood discharge capacity,underground pipeline,urban infrastructure and urban construction and other unsafe,bringing the huge potential harm to the good development of the city.Therefore,it is of great value to study the influencing factors of land subsidence in Beijing for its urban development,urban construction and disaster prevention and mitigation.The traditional land subsidence monitoring method can not carry out large-scale monitoring,and it is difficult to meet the needs of time and space scale.the traditional land subsidence monitoring method has not completely meet the land subsidence monitoring of the Beijing.SBAS-InSAR technology can effectively overcome the influence of temporal and spatial decoherence and atmospheric effect,and can monitor the small surface deformation for a long time with high accuracy.In order to grasp the situation of land subsidence in Beijing,including the location of subsidence area,the annual average subsidence rate and subsidence amount and etc.In this paper,we selected the Sentinel-1A descending image of 20 scenes C band covering the Beijing in 2017-2018 to extract the land subsidence rate and accumulated subsidence of the Beijing,and analyzed the causes of land subsidence in Beijing.The main research contents and conclusions of this paper are as follows:(1)Introducing D-InSAR technology and TS-InSAR technology in depth,and analysing the advantages and limitations of various methods.Finally,the SBAS-InSAR technology was selected to monitor the land subsidence in Beijing.The land subsidence monitoring results showed that there is still a large area of land subsidence in Beijing,and the overall decline trend is obvious.The subsidence areas are mainly concentrated in Haidian district,Chaoyang district,and Tongzhou district.The maximum annual average subsidence rate up to 120 mm/year.The former scattered subsidence area gradually expanded outward and developed in a funnel trend.(2)In the data processing process of TS-InSAR technology,due to GCPs are artificial selection,selection of different methods will result in the accuracy of GCPs are different,leading to obtain different Ground subsidence results.By selecting different GCPs for experiment,this paper puts forward the optimal selection method of GCPs in TS-InSAR technology,the GCPs are suitable to select regions with no residual topographic fringe,no phase jump and far from deformation information,and location distribution of uniform and reasonable number.(3)Using GPS data in the same period to verify the high reliability of the monitoring results obtained by SBAS-InSAR technology,which not only proves that the monitoring accuracy of InSAR technology reaches millimeter level,but also proves that the limited data applied by SBAS-InSAR technology can obtain high-precision monitoring results.(4)Collected the previous research results of land subsidence in Beijing and the geological,hydrological,GPS and other data of Beijing,and explored the formation reasons and development rules of land subsidence in the study area.Geological conditions and stratigraphic lithology are the internal conditions for the formation of land subsidence in Beijing,the main causes of land subsidence in Beijing are caused by overexploitation of groundwater,in addition that they are affected by land load,population factors,fault zones and other factors. |
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