Analysis Of Beijing Ground Subsidence Mechanism Based On SBAS-InSAR Technology

Since 1960 s Land Subsidence has been found in Beijing.Along with the advance of industrialization and expanding of city construction,the gradually increasing quantity of Land Subsidence in Beijing has become one of the threats to the city development and urban security.The engineers has built the Settlement Observation Monitoring Network for accurate data,which is using precise leveling as the main body and combined with the technology of GPS and InSAR.The Network provides important reference for urban planning,urban construction and disaster prevention.At present,traditional leveling is the main technical method of the Monitoring Network.Leveling has the advantages of mature technology,rich historical materials,relatively low cost equipment,and so on.But also has very obvious problems,such as long measuring period,relative sparse measurement points,high personnel cost and long period.Compared with traditional monitoring methods,InSAR has the advantages of reliable accuracy,large coverage,dense coherent point,short repetition period and continuous observation in a short time,due to the principle of its radar measurement.With 52 scenes of Envisat-ASAR images in 2003 to 2010 adopted and data processed by the SBAS technology,obtain the time series deformation rate diagram and the overall distribution of the subsidence in Beijing during the experiment time.Comparing with the leveling data,the result of ground subsidence rate and quantity by SBAS-InSAR method is equal to leveling.So the needs of general urban subsidence monitoring can also be satisfied by using SBAS-InSAR method.As the method of monitoring the city ground subsidence,the leveling and InSAR method are complementary to each other.In order to guarantee for urban construction and disaster prevention and reduction,the water resource changes and the national conditions of comprehensive geographical information should be monitored at the meantime.With the statistical analysis of coherent point,currently in Beijing there is not only a wide range of slow overall subsidence but also rapid partial subsidence.In terms of distribution,the subsidence in western,northern and eastern mountain is stable;the subsidence in city urban area is also small.But the area from southeast of Changping district to Chaoyang district and west of Tongzhou district has become a continuous subsidence area.And the trend has been extended to a large area of Daxing district in southern Beijing.The subsidence has a polycentric development pattern.The biggest subsidence areas are distributed in Chaoyang and Tongzhou district,which the largest cumulative subsidence is 847.5mm.With the comprehensive analysis of land subsidenceamountand fracture distribution chart and engineering geological data,geological structure and stratum lithology are the inner conditions and overall factors of the formation of Beijing land subsidence.Based on the relative analysis of the partial ground load distribution,the underground water monitoring data,water drop statistics data,the population change and SBAS-InSAR subsidence monitoring data,the external conditions and the controllable factors of the development of land subsidence are ground load,underground water changes and demographic factors.The direct cause of the rapid development of partial ground subsidence is partial underground water over-exploitation.Methods,such as controlling underground water exploitation and improving city development mode and so on,should be taken to prevent and control the ground subsidence.