Xuguo Shi

Characterization of Landslide Deformations in Three Gorges Area Using Multiple InSAR Data Stacks

In the areas with steep topography and vulnerable geological condition, landslide deformation monitoring is an important task for risk assessment and management. Differential Synthetic-Aperture Radar interferometry (D-InSAR) and Persistent Scatterer Interferometry (PS-InSAR) are two advanced SAR Interferometry techniques for detection, analysis and monitoring of slow moving landslides. The techniques can be used to identify wide displacement areas and measure displacement rates over long time series with millimeter-level accuracy. In this paper, multiple SAR datasets of Advanced Land Observing Satellite (ALOS) Phased Array L-band Synthetic Aperture Radar (PALSAR) and Environmental Satellite (ENVISAT) C-band Advanced Synthetic Aperture Radar (ASAR) are used for landslide monitoring with both D-InSAR and PS-InSAR techniques in Badong at the Three Gorges area in China. Two areas of significant deformation along the southern riverbank of Yangtze River in Badong are identified by joint analyses of PS-InSAR results from different data stacks. Furthermore, both qualitative and quantitative evaluations of the PS-InSAR results are carried out together with preliminary correlation analysis between the time series deformation of a PS point in high risk location and the temporal variation of water level in the Three Gorges Reservoir.

Expressway deformation mapping using high-resolution TerraSAR-X images

Monitoring deformation of linear infrastructures such as expressway and railway caused by natural processes or anthropogenic activities is a vital task to ensure the safety of human lives and properties. Interferometric Synthetic Aperture Radar (InSAR) has been widely recognized as an effective technology to carry out large-area surface deformation mapping. However, its application in linear infrastructure deformation monitoring has not been intensively studied till now. In this article, a modified Small BAseline Subset (SBAS) method is proposed to retrieve the deformation patterns of the expressway. In our method, only the point-like targets identified on the expressway were kept in our analysis, and two complementary subsets of interferograms were formed to better separate the signals of height error and deformation from inteferometric phase observations. We successfully applied this method with multitemporal high-resolution TerraSAR-X images to retrieve the spatial-temporal pattern of surface deformation along the Bei’an-Heihe expressway that is located in island-permafrost areas and threatened by geohazards.

Wide-Area Landslide Deformation Mapping with Multi-Path ALOS PALSAR Data Stacks: A Case Study of Three Gorges Area, China

In recent years, satellite synthetic aperture radar interferometry (InSAR) has been adopted as a spaceborne geodetic tool to successfully measure surface deformation of a few well-known landslides in the Three Gorges area. In consideration of the fact that most events of slope failure happened at places other than those famous landslides since the reservoir impoundment in 2003, focusing on a limited number of slopes is insufficient to meet the requirements of regional-scale landslide disaster prevention and early warning. As a result, it has become a vital task to evaluate the overall stability of slopes across the vast area of Three Gorges using wide-coverage InSAR datasets. In this study, we explored the approach of carrying out joint analysis of multi-path InSAR data stacks for wide-area landslide deformation mapping. As an example, three ALOS (Advanced Land Observing Satellite) PALSAR (Phased Array type L-band Synthetic Aperture Radar) data stacks of neighboring ascending paths covering the area along the Yangtze River from Fengjie to Zigui were analyzed. A key problem to be solved is the separation of the tropospheric signal from the interferometric phase, for which we employed a hybrid description model of the atmospheric phase screen (APS) to improve APS estimation from time series interferograms. The estimated atmospheric phase was largely correlated with the seasonal rainfall in the temporal dimension. The experimental results show that about 30 slopes covering total areas of 48 km2 were identified to be landslides in active deformation and should be kept under routine surveillance. Analyses of time series displacement measurements revealed that most landslides in the mountainous area far away from Yangtze River suffered from linear deformation, whereas landslides located on the river bank were destabilized predominantly by the influences of reservoir water level fluctuation and rainfall.

Landslide Deformation Analysis by Coupling Deformation Time Series from SAR Data with Hydrological Factors through Data Assimilation

Time-series SAR/InSAR techniques have proven to be effective tools for measuring landslide movements over large regions. Prior studies of these techniques, however, have focused primarily on technical innovation and applications, leaving coupling analysis of slope displacements and trigging factors as an unexplored area of research. Linking potential landslide inducing factors such as hydrology to SAR/InSAR derived displacements is of crucial importance for understanding landslide deformation mechanisms and could support the development of early-warning systems for disaster mitigation and management. In this study, a sequential data assimilation method named the Ensemble Kalman filter (EnKF), is adopted to explore the response mechanisms of the Shuping landslide movement in relation to hydrological factors. Previous research on the Shuping landslide area shows that the reservoir water level and rainfall are the two main triggering factors in slope failures. To extract the time-series deformations for the Shuping landslide area, Pixel Offset Tracking (POT) technique with corner reflectors was adopted to process the TerraSAR-X StripMap (SM) and High-resolution Spotlight (HS) images. Considering that these triggering factors are the primary causes of displacement fluctuations in periodic displacement, time-series decomposition was carried out to extract the periodic displacement from the POT measurements. The correlations between the periodic displacement and the inducing factors were qualitatively estimated through a grey relational analysis. Based on this analysis, the EnKF method was adopted to explore the response relationships between the displacements and triggering factors. Preliminary results demonstrate the effectiveness of EnKF in studying deformation response mechanisms and understanding landslide development processes.

Deformation monitoring of slow-moving landslide with L- and C-band SAR interferometry

SAR interferometry (InSAR) is an effective tool for wide-area earth surface deformation detection and mapping. In this letter, Persistent Scatterers InSAR method was employed to derive the deformation histories of Huangtupo and Zhaoshuling landslides located in Badong County of the Three Gorges area. One Environmental Satellite C-band Advanced Synthetic Aperture Radar (ASAR) data stack acquired from descending orbit and two Advanced Land Observation Satellite Phased Array type L-band Synthetic Aperture Radar (PALSAR) data stacks collected from two adjacent ascending orbits were used. Different deformation trends were observed from the descending and ascending data stacks. Disagreements were found on Huangtupo and Zhaoshuling landslides between measurements of ASAR data and PALSAR data, which might be primarily attributed to different viewing geometries. Meanwhile, due to smaller decorrelation effects for longer wavelength, L-band PALSAR data can be used to detect more point-like targets than C-band ASAR data, which makes it more suitable for monitoring landslides in vegetated areas such as the Three Gorges. Preliminary temporal correlation analyses between deformation measurements and water level fluctuation as well as rainfall were performed to explore the driving mechanism for landslide motion within the Three Gorges Reservoir area.

Landslide Displacement Monitoring with Split-Bandwidth Interferometry: A Case Study of the Shuping Landslide in the Three Gorges Area

Landslides constitute a major threat to people’s lives and property in mountainous regions such, as in the Three Gorges area in China. Synthetic Aperture Radar Interferometry (InSAR) with its wide coverage and unprecedented displacement measuring capabilities has been widely used in landslide monitoring. However, it is difficult to apply traditional InSAR techniques to investigate landslides having large deformation gradients or moving primarily in north-south direction. In this study, we propose a time series split-bandwidth interferometry (SBI) procedure to measure two dimensional (azimuth and range) displacements of the Shuping landslide in the Three Gorges area with 36 TerraSAR-X high resolution spotlight (HS) images acquired from February 2009 to April 2010. Since the phase based SBI procedure is sensitive to noise, we focused on extracting displacements of corner reflectors (CRs) installed on or surrounding the Shuping landslide. Our results agreed well with measurements obtained by the point-like targets offset tracking (PTOT) technique and in-situ GPS stations. Centimeter level accuracy could be achieved with SBI on CRs which shows great potential in futures studies on fast moving geohazards.

Monitoring Landslide Activities in the Three Gorges Area with Multi-frequency Satellite SAR Data Sets

Thousands of landslides are distributed along Yangtze River and its tributaries in the Three Gorges area from Chongqing Municipality in the west to Hubei Province in the east (P.R. China). Since the construction and regular operation of the Three Gorges Dam in the past two decades, many ancient landslides have been reactivated and some new landslides were formed along with the unprecedentedly huge water-level changes. Monitoring landslide activities has then been considered as a high-priority task for geological disaster prevention and management in the reservoir area, while traditional monitoring methods can hardly meet the requirements. In this chapter, we investigated the applications of several methods using Synthetic Aperture Radar (SAR) datasets in landslide monitoring in the Three Gorges area. Multifrequency satellite SAR data sets acquired by ENVISAT/ASAR, ALOS/PALSAR, and TerraSAR-X from different orbits were analyzed to retrieve historic deformations of a few typical landslides. The experimental results suggested that SAR Interferometry (InSAR) methods can be effectively used to monitor slow-moving landslides, while pixel offset tracking method is more suitable for detecting deformation of fast-moving landslides. Furthermore, qualitative correlation analyses indicated that variation of reservoir water level, particularly the rapid water-level decrease due to discharge, should be identified as a key driving factor for landslide deformation in the Three Gorges area.

Detection of coal-mining-induced subsidence and mapping of the resulting deformation using time series of ALOS-PALSAR data

ABSTRACT Land subsidence caused by extracted void collapses due to coal mining activities is a major geohazard in northern China. Differential SAR interferometry (DInSAR) has been adopted as an effective tool for coal mining subsidence detection and deformation mapping. However, previous studies were mostly focused on the derivation of linear deformation rates in coal mines, while the spatial–temporal pattern of coal mining subsidence and its interaction with the fault systems have rarely been investigated. In this study, ALOS-PALSAR images acquired from 19 June 2007 to 12 November 2010 were analysed with DInSAR and small baselines subset (SBAS) techniques to characterize the distribution and magnitude of subsidence in central Henan province, which is one of the leading coal producers in China. More than 40 funnel-shaped subsidence areas distributed within the coalfields have been detected in both Dengfeng and Xinmi. The maximum annual mean deformation can be as high as 8 cm in the line-of-sight (LOS) direction. Deformation maps were generated in the study area, showing an extended subsidence of 2009 compared with that of 2007. We also analysed the deformation profiles perpendicular to the faults, and found an asymmetric subsidence pattern along the profiles. Such a pattern may be an indicator of local fault activities, and it may help understanding of coal mine subsidence near faults.

Retrieval of time series three-dimensional landslide surface displacements from multi-angular SAR observations

A major limitation for wide application of Synthetic Aperture Radar (SAR) remote sensing in mapping landslide surface displacements is the intrinsic gap between the ultimate objective of measuring three-dimensional displacements and the limited capability of detecting only one or two-dimensional displacements by repeat-pass SAR observations of identical imaging geometries. Although multi-orbit SAR observations of dissimilar viewing geometries can be jointly analyzed to inverse the three-dimensional displacements, the reliability of inversion results might be highly questionable in case of continuous motion because of the usually asynchronous acquisitions of multi-orbit SAR datasets. Aiming at this problem, we proposed an approach of retrieving time series three-dimensional displacements from multi-angular SAR datasets for step-like landslides in the Three Gorges area in this article. Firstly, time series displacements of a common ground target in the azimuth and line-of-sight (LOS) direction can be estimated using traditional methods of SAR interferometry (InSAR) and SAR pixel offset tracking (POT), respectively. Then, a spline fitting and interpolation procedure was employed to parameterize the displacement history in the sliding/dormant periods of step-like landslides and estimate displacements from multi-angular observations for identical date series. Finally, three-dimensional displacements can be inverted from these synchronized multi-angular measured displacements in traditional ways. As a case study, the proposed method was applied to retrieve the three-dimensional displacements history of the Shuping landslide in the Three Gorges area, China. Comparisons between SAR-measured displacements and measurements of global positioning system (GPS) showed good agreement. Furthermore, temporal correlation analyses suggest that reservoir water level fluctuation and rainfall are the two most important impact factors for the Shuping landslide stability.

Landslides analysis in western moutainous areas of China using Distributed Scatterers based InSAR

Multiple InSAR techniques are increasingly being developed for earth observation. However, among them, persistent scatterers-based InSAR (PSI) techniques fail to obtain enough measurement points (MPs) in rural mountainous area due to the lack of persistent scatterers (PSs), such as ma-made structures, rocks, and outcrops, etc. In this paper, Distributed Scatterers-based InSAR (DS-InSAR) algorithm, exploiting both persistent scatterers and distributed scatterers (DSs) widely spreading in rural areas, is proposed to make up the limitation of persistent scatterers-based technique when monitoring mountainous landslides. There are two key steps to preprocess DSs in DS-InSAR algorithm: selecting DS candidates and estimating optimal interferometric phases. The selected DSs and PSs are combined for further processing using traditional PSI procedure. A qualitative and quantitative simulation analysis was operated to validate the DS-InSAR algorithm. Then, both PSI and DS-InSAR were implemented to monitor Xishan landslide in western mountainous region of Sichuan province, based on high-resolution TerraSAR-X images. The obtained results demonstrate that DS-InSAR could detect much more MPs and provide more reliable deformation information.