Detecting Ground Deformation And Investigating Landslides Using InSAR Technique

Landslides cause more and more significant structural,social and economic impacts,particularly in areas under pressure from ongoing urbanization and infrastructure development.It is necessary to exploit efficient method to investigate landslide hazard at regional scale.As the most significant and comprehensive parameters in different stages of landslide occurrence,development and evolution,displacement of landslide could be used to investigate,assess and predict landslides accuracy and reliably.Conventional displacement observations mostly detect ground deformation at point or small region,which are less effective and applicable to monitor and investigate displacements of landslide at regional scale.The Interferometric Synthetic Aperture Radar(InSAR)technique is one of the most efficient methods for ground deformation monitoring,landslide observation,interpretation and assessment at regional scale,due to its large coverage,high spatial resolution,high accuracy,and long-term acquisition under all weather conditions.However,it is still a challenge to monitor ground deformation and investigate landslide in mountainous area.In addition,no exist complete method system based on InSAR could be used to investigate,assess and reduce landslide hazard.In order to overcome aforementioned limitations and problems,this study demonstrates the advantages and limitations of InSAR-derived ground deformation time-series and mapping/characterization of landslides in Bailong River Basin,which is one of four areas in China most severely impacted by landslides and debris flows.Moreover,this study is devoted to build a method system to investigate landslide hazards based on InSAR and guide geohazards management.The main results are as follows:(1)The feasibility of monitoring ground deformation of Bailong River Basin with satellite Synthetic Aperture Radar(SAR)data was assessed by analyzing ENVISAT ASAR,ALOS PALSAR,COSMO SKYMED and SENTINEL archive data availability and geometric distortions on the success of InSAR analysis.The results show that ascending data have better visibility on east-facing slope,while descending data have better visibility on west-facing slope.The area of geometric distortions of SAR image decreases with the increase of incidence angle of radar sight.In case of all available SAR imagery in Bailong River Basin,the combination of ascending and descending data from SENTINEL satellite have the best visibility.All available SAR data from different satellite could be used to detect ground deformation and investigate landslides in Bailong River Basin.(2)The use of combined of multiple InSAR technologies overcome the problems of poor coherence of radar signals and obtain the ground deformation from 2003 to 2010 in millimeter precision.Having verified through field investigations and ground monitoring results,133 unstable slopes have been identified,of which 33 are exist landslides and 100 are unstable slopes.The deformation differences at the different parts of typical landslides are detected.The research has also revealed the relationship and interactions between time-series displacement and rainfall and earthquake.(3)The Zhouqu region is a mountainous area in the Bailong River Basin(Gansu,China)where mass movements dominate the geomorphology and impact lives and livelihoods.However,the topographic,geological,hydrological,geomorphological processes and their connections to geohazards in this landscape remain poorly understood.Improving this understanding is aided by the construction of a geomorphological map based on integrated remote sensing,spatial analysis,hydrological analysis,fieldwork,and literature reviews.The resulting map informs a description of the geomorphological processes with an emphasis on categorisation and characterisation of mass movement geohazards.Three geomorphological domains are distinguished,separated by active faults and Bailong River,and comprising two mountainous domains dominated by hard and soft bedrock lithologies and a central valley corridor where large mass movements develop in soft rock lithologies.The main controls for the initiation and ongoing activity of geohazards in this landscape include a combination of active faults,lithology,hill-slope processes,rainfall and human activity.(4)Multi-sensor and multi-temporal SAR data were used to monitoring ground deformation from 2007 to 2017 in Zhouqu region.The monitoring capacity revealed that InSAR could detect displacements of 63(81% of total mapped landslides)mapped landslides,which include 52 active landslides.Moreover,277 landslides and unstable slopes which were not mapped in geomorphological map and exist literatures were investigated.The activity and intensity of all landslides and unstable slopes were assessed based on ground deformation velocities derived by InSAR technique.The activity results show that 328 landslides or unstable slopes are active or reactivated,and 15 landslides or unstable slopes are stabilized or dormant.The intensity results show that 218 landslides or unstable slopes are very slow,113 landslides or unstable slopes are extremely slow,and 14 landslides are negligible.The distribution and activity of 11 large fragmented bedrock landslides exploits geological weaknesses in the faultcontrolled belt of low-grade metamorphic rocks of the Bailong valley and severely impacts lives and livelihoods in this region.In the long-term,the movement of these landslides results in a local relief with characteristic slope angles lower than before controlled by an equilibrium between available shearing resistance,and precipitationinduced pore pressure variations coupled with additional stresses induced by periodic seismic acceleration resulting from regional earthquake activity.(5)The spatial and temporal motion patterns of Suoertou landslide were distinguished based on velocity map and time-series displacement generated by multiInSAR technique.The ground deformation velocity map and geomorphological map of Suoertou enables segmentation of the major landslide body into five deformation zones.In case of the kinematic patterns,the major landslide body could be divided into two transport zones and two accumulation zones.Time series analysis of the Souertou landslide reveals that seasonal velocity changes are characterized by comparatively rapid acceleration and gradual deceleration with distinct kinematic zones with different mean velocities,although velocity changes appear to occur synchronously along the landslide body over seasonal timescales.The observations suggest that the post-seismic effects(acceleration period)on landslide deformation last some 6-7 months.In conclusion,the InSAR technique is much more advanced than the traditional single-point monitoring technique for landslides,which could forecast the location and extension,and investigate the spatial and temporal motion patterns of landslides,demonstrating and extending the ability and applicability of InSAR technique.The ground deformation derived by InSAR technique fills the gaps of long-term displacement monitoring for landslides in Bailong River Basin.The landslides investigation,assessment and motion patterns observation results in an enhanced capacity to design,construct and manage appropriate landslide risk reduction infrastructure and strategies.This study provides foundation and a classic example for landslide research based on InSAR in similar area.