Time-series InSAR Technique For Monitoring Frozen Soil Deformation Along The Qinghai-Tibet Railway In The Northern Sanjiangyuan Area

Frozen soil is a complex multiphase system with extremely unstable water,heat and stress properties,which is characterized by high levels of spatial heterogeneity and poor stability.Global warming and human activities continue to affect the dynamic balance of the Qinghai-Tibet Plateau(QTP)frozen soil environment,thus affecting the safety and stability of its infrastructure.Therefore,it is of great practical significance to monitor the seasonal deformation and thawing features of frozen soil on the QTP based on certain monitoring tools.The Qinghai-Tibet Railway(QTR)is the highest and longest linear structure on the plateau in the world.The complex and diverse geomorphic landscape along the QTR,with alternating seasonally frozen soil and permafrost,makes the research of frozen soil by traditional monitoring methods inefficient and costly.Interferometric Synthetic Aperture Radar(InSAR)is characterized by high-precision and high-density acquisition,allowing deformation monitoring of frozen soil in a wide range on seasonal and long time scales.This thesis applies the Small baseline subset Interferometric Synthetic Aperture Radar(SBAS-InSAR)method to investigate frozen soil two-dimensional(2D)deformation field along the Qinghai-Tibet Railway in the northern Sanjiangyuan area.The temporal and spatial distribution characteristics of frozen soil deformation,influencing factors,and its relationship with climate change are researched,providing reference and technical guidance for the research on environmental governance and disaster assessment in this area.The main research contents of this thesis are as follows:(1)Due to the limitation of radar imaging geometry,the traditional InSAR technology can only get the deformation information of the surface line of sight,which is difficult to reflect the actual deformation characteristics of the surface.Based on the SBAS-InSAR method,110 Sentinel-1A ascending and descending SAR images are employed to derive the deformation results of frozen soil in two LOS directions in the research area from 2017 to2021.Combined with the geometric parameters of the SAR system,the 2D deformation results of frozen soil are calculated.(2)Based on the daily surface deformation monitoring data from the Global Navigation Satellite System(GNSS)at the QHTT Reference Station,this research verifies the accuracy of 2D deformation monitoring results and analyses the applicability of the InSAR technology for monitoring frozen soil deformation in the research area.(3)Based on the calculated 2D deformation results of InSAR,this research analyzes the spatial distribution characteristics of frozen soil deformation in combination with external conditions and internal factors that affect the stability of frozen soil.The analysis results show that the deformation of frozen soil with different topographic and geomorphic conditions in the vertical and east-west directions is significantly different.(4)For crucial monitoring areas,this study analyses the long-term changes of frozen soil deformation based on the InSAR deformation results in the vertical direction from early ALOS-1 SAR images,the known information of thawing hazards,and historical satellite images.It is found that the continuous development of thawing hazards posed a significant threat to the stability of the Qinghai-Tibet engineering.(5)The seasonal components of the GNSS and InSAR results of the QHTT station in the vertical direction are extracted using a time series decomposition model and compared with the daily climate change data.It is found that both sets of results are consistent with the existing climate change law,which can reflect the freeze-thaw cycle of frozen soil.