Application Research Of Landslide Monitoring In Ahai Reservoir Area Based On Time Series InSAR Technology

China is a country prone to geological disasters,among which landslide is one of the most serious disasters.The southwest mountain area is rich in water system and numerous water conservancy projects,but because of the complex and changeable terrain and the fragile geological structure,landslide disasters occur frequently,which brings huge potential hazards to the safety of projects and personnel.Traditional deformation monitoring methods have many limitations.Time-series InSAR technology has been widely used in large-scale detection and high-precision monitoring of geological hazards due to its advantages such as high timeliness,low cost and wide area coverage.The selection of interference pair is an important step in time-series InSAR technique,and its interference combination affects the accuracy of phase unwrapping and deformation analysis results.At present,InSAR technology has good reliability in the application of subsidence monitoring with a small deformation gradient.However,for the monitoring of landslide disaster with a large surface deformation gradient,errors may occur due to improper combination of interference pairs during phase unwinding,resulting in a large gap between the calculated results and the real deformation.For this reason,this paper summarizes and analyzes the main problems existing in the application of time-series InSAR technology mountain landslide monitoring,selects the Xin Jian landslide body with the most severe landslide along the Ahai Reservoir in the middle reaches of Jinsha River to conduct experiments,and analyzes the landslide characteristics.The main contents and results are as follows:(1)In view of the inaccuracy of phase unwinding due to the large deformation gradient in the monitoring of landslides in mountainous areas,and the problem that the results cannot accurately reflect the deformation of the real surface,this paper proposes the combined optimization strategy of interference pair:(1)The space-time baseline threshold should ensure that the maximum number of interference pairs can be generated,satisfying the interference pairs that can retain the first(front)5 scenes and the last(rear)5 scenes.(2)For each scene image,on the premise of ensuring the quality,only 5 connections are retained.In this case,the connection should not only include the interference pair when the image is the master image,but also include the interference pair when the image is the slave image.(2)Using the optimized interference pair combination strategy and the conventional selection method,the SBAS-InSAR technology was used to process the62 landscape rising orbit images covering the study area,and the deformation field between 2018.4.6 and July,2020.4.7 was obtained.The results show that the shape variables of the two methods are relatively consistent for the non-landslide area,and the difference is great for the landslide area.For the newly built landslide,the deformation rate of the conventional method is 40-70mm/a from 2018.4.6 to 2019.4.1(the first period),and 35-90mm/a from April 2019.4.13(the second period).After optimization,it is 57-189mm/a in the first period and 52-193mm/a in the second period.(3)Introducing GPS monitoring results during this period,the landslide deformation results of the two methods is compared,the projection to the line of sight to the conventional method with the results of GPS on the order of magnitude difference about 2 to 3 times,no multiple differences after optimization,is closer to the GPS on the accuracy of the results,combined with field investigation,analysis of previous studies,the research results show that the optimized results of InSAR and GPS have consistency,based on the interference of optimal selection of InSAR technology for Xin Jian landslide deformation monitoring with reliability.(4)Combined with the geological survey data and rainfall data,the temporal and spatial characteristics of the landslide are analyzed,and the causes of deformation are preliminarily discussed.The research results show that the boundary of the three deformation zones is consistent with the distribution of the four gully fractures found in the geological exploration.Under the influence of the rainy season,the deformation characteristics show a periodic change of stabilization—acceleration—stabilization—acceleration.