Comparative research and its significance of deformation measurements by technologies of laser real-time holographic interferome-try and radar differential interferometry

The principles and applications of laser real-time holographic interferometry （LRTHI） and radar differential interferometry （RDI） technologies are described in this paper, respectively. By using LRTHI, we can observe the deformation of samples under pressure in the lab and study the anomaly characteristics relating to different strain fields in different fracture-developing areas; while by using RDI, we can observe the landform and surface deformation. The results of deformation observed before and after the Ms=7.9 Mani earthquake （Tibet） and Ms=6.2 Shangyi-Zhangbei earthquake in China are obtained. It is pointed out that LRTHI and RDi are similar, which study the characteristics of anomalous deformation field by fringe variations for both of them. Therefore, the observation of deformation field in the seismogenic process, especially in the period impending an earthquake by RDI, and the comparative study in the lab by LRTHI are of great significance.

Ground Surface Ruptures and Near-Fault,Large-Scale Displacements Caused by the Wenchuan Ms8.0 Earthquake Derived from Pixel Offset Tracking on Synthetic Aperture Radar Images

The 12 May 2008 Wenchuan Ms8.0 earthquake produced surface displacements along the causative fault, the Yingxiu-Beichuan Fault, which are up to several meters near the fault. Because of the large gradient, satellite synthetic aperture radar （SAR） interferometric data are strongly incoherent; the usual SAR interferometry method does not allow such displacements to be measured. In the present study, we employed another approach, the technique based on pixel offset tracking, to solve this problem. The used image data of six tracks are from the Advanced Land Observing Satellite, Phased Array type L-band Synthetic Aperture Radar （ALOS/PALSAR） dataset of Japan. The results show that the entire surface rupture belt is 238 km long, extending almost linearly in a direction of 42°north-east. It is offset left laterally by a north-west-striking fault at Xiaoyudong, and turns at Gaochuan, where the rupture belt shifts toward the south by 5 km, largely keeping the original trend. In terms of the features of the rupture traces, the rupture belt can be divided into five sections and three types. Among them, the Beichuan-Chaping and Hongkou-Yingxiu sections are relatively complex, with large widths and variable traces along the trend. The Pingtong-Nanba and Qingping-Jingtang sections appear uniform, characterized by straight traces and small widths. West of Yingxiu, the rupture traces are not clear. North of the rupture belt, surface displacements are 2.95 m on average, mostly 2-3.5 m, with 7-9 m the maximum near Beichuan. South of the rupture belt, the average displacement is 1.75 m, dominated by 1-2 m, with 3-4 m at a few sites. In the north, the displacements in the radar line of sight are of subsidence, and in the south, they are uplifted, in accordance with a right-slip motion that moves the northern wall of the fault to the east, and the southern wall to the west, respectively. Along the Guanxian-Jiangyou Fault, there is a uplift zone in the radar line of sight, which is 66 km long, 1.5-6 km wide, and has vertical displacements of approximately 2 m, but no observable rupture traces.

Monitoring elevation change of glaciers on Geladandong Mountain using Tan DEM-X SAR interferometry

Glaciers play an important role in the climate system. The elevation change of a glacier is an important parameter in studies of glacier dynamics. Only a few ground-based measurements of high mountain glaciers are available due to their remoteness, high elevation, and complex topography. The acquisition from the German Tan DEM-X(Terra SAR-X add-on for Digital Elevation Measurement) SAR imaging configuration provides a reliable data sources for studying the elevation change of glaciers. In this study, the bistatic Tan DEM-X data that cover the Geladandong Mountain on the Tibetan Plateau were processed with SAR interferometry technique and the elevation changes of the mountain's glaciers during 2000–2014 were obtained. The results indicated that although distinct positive and negative elevation changes were found for different glacier tongues, the mean elevation change was about-0.14±0.26 m a-1. Geoscience Laser Altimeter System(GLAS) data were obtained for comparison and verification. The investigation using GLAS data demonstrated the efficacy of the proposed method in determining glacier elevation change. Thus, the presented approach is appropriate for monitoring glacier elevation change and it constitutes a valuable tool for studies of glacier dynamics.

Post-Processing of InSAR Deformation Time Series Using Clustering-Based Pattern Identification

Multi-temporal synthetic aperture radar interferometry(MT-InSAR)is a standard technique for mapping clustering and wide-scale deformation.A linear model is often used in phase unwrapping to overcome the underdetermination.It’s difficult to identify different types of nonlinear deformation.However,the interpretation of nonlinear deformation is very important in monitoring potential risk.This paper introduces a comprehensive approach for identifying and interpreting different types of deformation within InSAR datasets,integrating initial clustering and classification simplification.Initial classification is performed using the K-means clustering method to cluster the collected InSAR deformation time-series data.Then we use F test and Anderson-Darling test(AD test)to simplify the clusters after initial classification.This technique distinctly discerns the changing trends of deformation signals,thereby providing robust support for interpreting potential deformation scenarios within observed InSAR regions.

Environmental Investigation and Evaluation of Land Subsidence in the Datong Coalfield Based on InSAR Technology

Heavy mining of Jurassic and Carboniferous horizontal coal seams in the Datong coalfield has seriously affected the local geological environment, which is mainly manifested by such geohazards as soil avalanches, landslides, mudflows, surface subsidence, surface cracks, surface solid waste accumulation and surface deformation. More seriously, coal mining causes groundwater to leak. Overpumping of groundwater has resulted in substantial land subsidence of the urban area in Datong City. Based on the previous geo-environmental investigation in the work area, the authors used radar remote sensing techniques such as InSAR （synthetic aperture radar interferometry） and D-InSAR （differential synthetic aperture radar interferometry）, supplemented by the optical remote sensing method, for geo-environmental investigation to ascertain the geo-environmental background of the Datong Jurassic and Carboniferous-Permian coalfield and evaluate the effects of the geohazards, thus providing a basis for the geo-environmental protection, geohazard control and prevention, land improvement and optimization of the human environment. In this study 8 cog-nominal ERS-1/2 SAR data frames during 1992 to 2003 were used, but the following processing was made： （1） the multitemporal SAR magnitude images were used to interpret the geological structure, vegetation, microgeomorphology and drainage system; （2） the multi-temporal InSAR coherent images were used to make a classification of surface features and evaluate the coherence change due to coal mining; and （3） the multi-temporal cog-nominal SAR images were used to complete D-InSAR processing to remove the information of differential deformation areas （sites）. In the end, a ten-year time series of differential interferograms were obtained using the multi-temporal cog-nominal SAR images. In the tests, 84 deformed areas （sites） were obtained, belonging to those in 1993-1996, 1996-1997, 1997-1998, 1998-2001, 1998-2002 and 2001-2003 respectively. Of the 84 areas, 44 are mining subsidence ones, 23 urban subsidence ones and 17 landslide subsidence ones. They cover a total area of 1824.4 km^2, equivalent to the area of the whole Datong coalfield. Then an accurate evaluation was made on the geo-environment of the Datong coalfield. The tests show that InSAR is now the only feasible technical means for making one all-weather, real-time measurement of a coal mining land subsidence area covering up to 10,000 km^2 to subcentimeter resolution. This study is a successful application of InSAR in the investigation and evaluation of land subsidence, especially in coal mining areas.

Study on crustal deformation of the Ms6.6 Damxungearthquake in 2008 by InSAR measurements

Three Envisat images from ESA were used to derive the pre - and co-seismic deformation interfereograms caused by the Damxung Ms6. 6 earthquake of Oct. 6,2008 ,by using InSAR. The result shows no significant crustal motion more than 4 months before the earthquake, but a maximum co-seismic displacement of about 0.3 m in an epicentral area of 20 km × 20 km. The deformation field was symmetrically distributed about a NS axis, where the west side subsided and the east side uplifted. We used a linear elastic dislocation model in half space and a nonlinear constraint optimized algorithm to estimate the slip distribution along the fault. The results indicates that the epicenter is located at 90. 374°E ,29. 745°N with a moment magnitude of Mw6. 35. The earthquake is dominated by normal faulting with a maximum slip of 3 m on a 12 km × 11 km fault plane striking S189°W,dipping 60° to NW at a depth of 9.5 km,and is located at a sub-fault of the southeastern Piedmont of the Nyainqentanglha mountains. The relatively shallow depth of earthquake is related to relatively high heat flow in the area.

Quantifying glacial elevation changes in the central Qilian Mountains during the early 21^(st) century

Glaciers in the central Qilian Mountains provide important water resources for the arid Hexi corridor and Qaidam Basin;however,changes in these glaciers interact with climate change.Twenty-four bi-static image pairs of TerraSAR-X add-on for Digital Elevation Measurement(TanDEM-X)data,in addition to a Shuttle Radar Topography Mission-C/X band digital elevation model,and the technology of iterative differential synthetic aperture radar interferometry were used to carry out glacier elevation change analysis in the central Qilian Mountains in China during 2000–2014.Glacier elevation changed with an average rate of(−0.47±0.06)m yr^(−1),while changes in elevation of(−0.51±0.06)m yr^(−1) and(−0.44±0.06)m yr^(−1) were found in the northern(including the Zoulangnan,Tuolai,and Tuolainan mountains)and southern(including the Shulenan and Hark mountains)regions,respectively.Summer mean temperature has risen by 0.51℃(10 yr)^(−1)in the northern region and 0.48℃(10 yr)^(−1) in the southern region during 1989–2014;however,the change in amplitude of annual precipitation was 2.69 mm yr^(−1) in the northern region and 4.77 mm yr^(−1) in the southern region for the same period.These changes can be ascribed as major driving factors for the differences in the changes in glacial elevation in the northern and southern regions.Four types of glaciers existed in the region when considering the change in elevation of the glacial tongue and variation in the position of the glacial terminus:surging,advancing,intensively retreating,and slightly retreating glaciers.If elevation decreased more than 20 m on the part of glacier tongue,the glacier terminus position had commonly retreated more than 100 m.

An easy approach to assess the susceptibility of a landslide by utilizing simple raster overlay methods: A case study on Huangtupo landslide(P.R. China)

Semi qualitative index based methods using rankings and ratings are commonly used in susceptibility estimations over a wide area. However, generalized ranking and ratings are not applicable for one single landslide. This paper gives an easy and transferable approach to a susceptibility assessment of Huangtupo landslide(P.R. China), using raster addition without taking account for ranking and ratings. Slope, aspect, curvature, location and drainage buffer distance raster data sets have been obtained out of open source digital elevation models using ESRI's Arc GIS. These conditioning factor raster data sets have been translated into raster data sets including simple yes or no criteria, referring to triggering or not. Subsequently they have been added by raster math to acquire a simple raster overlay map.After that this map is compared to initial displacement measurements, obtained by using a ground based synthetic aperture radar device. Acquired data is recalculated to a raster data set using the same spatial extent, to provide the possibility of comparison of the two raster data sets. The results reveal, that 76.35% of all measured movements occur in areas where raster cells include three or more conditioning factors, indicating that easy raster math operations can lead to satisfying results in local scale.

Robust PolInSAR optimal interferogram estimation method based on generalized scattering vector

For the polarimetric synthetic aperture radar interferometry (PoIInSAR) processing, it is necessary to coregister all the images, including the coregistration of polarimetric SAR images and the coregistration of interferometric SAR images. Otherwise, the performance of the estimated optimal interferograms will be deteriorated. A generalized scattering vector (GSV) model is proposed to execute the PoIInSAR optimal interferograms estimation. The generalized scattering vector is constructed by the Pauli scattering vectors of the processing pixel and the surrounding pixels. Even though there are coregistration errors, all the polarimetric information of the current processing pixel is entirely included in the generalized scattering vector. Therefore, the GSV-based method can automatically recover the optimal scattering mechanisms of the processing pixel with coregistration errors either in interferoemetric channels or polarimetric channels. Theoretical analysis and processing results of simulated PoISARPro data and real PALSAR data validate the effectiveness and correctness of the proposed method.

KEY TECHNOLOGY OF D-INSAR AT X-BAND FOR MONITORING LAND SUBSIDENCE IN MINING AREA AND ITS APPLICATION

In theory, land subsidence measurement results with high accuracy can be obtained by using the Differential Interferometry Synthetic Aperture Radar(D-InSAR) at X-band. In practice, however, the measuring accuracy of D-InSAR at X-band has been seriously affected by some factors, e.g., decorrelation and high deformation gradient. In this work, the monitoring capability of D-InSAR for coal-mining subsidence is evaluated by using SAR data acquired by TerrraSAR-X system. The SAR image registration method for low coherence image pairs, the denoising phase filter for high noise level interferogram and atmospheric effects mitigation method are the key technical aspects which directly influence the measurement results of D-InSAR at X-band. Thus, a robust image registration method, an improved phase filter method and an atmospheric effects mitigation method are proposed in this paper. The proposed image registration method successfully achieves InSAR coregistration, while the amplitude cross-correlation cannot properly coregister low coherence SAR image pairs. Moreover, the time complexity of the proposed image registration method is obviously slighter than that of the Singular Value Decomposition(SVD) method. The comparing experiment results and the unwrapping phase results show that the improved Goldstein filter is more effective than the original Goldstein filter in noise elimination. The atmospheric influence correction experiment results show that the land subsidence areas with atmospheric influence correction are more clarified than that of without atmospheric influence correction. In summary, the presented methods directly improved the measurement results of D-InSAR at X-band.

Decomposing InSAR LOS displacement into co-seismic dislocation with a linear in-terpolation model: A case study of the Kunlun Mountain M_s=8.1 earthquake

It has always been a difficult problem to extract horizontal and vertical displacement components from the InSAR LOS （Line of Sight） displacement since the advent of monitoring ground surface deformation with InSAR technique. Having tried to fit the firsthand field investigation data with a least squares model and obtained a preliminary result, this paper, based on the previous field data and the InSAR data, presents a linear cubic interpolation model which well fits the feature of earthquake fracture zone. This model inherits the precision of investigation data; moreover make use of some advantages of the InSAR technique, such as quasi-real time observation, continuous recording and all-weather measurement. Accordingly, by means of the model this paper presents a method to decompose the InSAR slant range co-seismic displacement （i.e. LOS change） into horizontal and vertical displacement components. Approaching the real motion step by step, finally a serial of curves representing the co-seismic horizontal and vertical displacement component along the main earthquake fracture zone are approximately obtained.

Retrieving the grounding lines of the Riiser-Larsen Ice Shelf using Sentinel-1 SAR images

Accurately locating and studying grounding lines is essential for predicting the response of glaciers to climate change.However,it is challenging tofind grounding lines since they are subglacial features.In this study,Sentinel-1 synthetic aperture radar(SAR)data were utilized to derive the grounding lines of the Riiser-Larsen Ice Shelf.A new method with inspiration drawn from multi-temporal baseline InSAR techniques is proposed.It takes advantage of the temporal consistency of the vertical displacement gradients and identifies grounding zones pixel-by-pixel on a stack of double differential interferograms,thereby providing grounding line proxies.As it fully exploits coherent signals in both spatial and temporal domains,the maximum possible number of grounding zone pixels can be obtained.Moreover,due to the introduction of the concept of the temporal consistency,the method can cope with short term grounding linefluctuations to some extent and may mitigate the influences of atmospheric disturbances and residual ice displacements.The resulting grounding lines are compared with the MEaSUREs Antarctic grounding line product.The comparison confirms the effectiveness of the proposed method and corroborates that the Riiser-Larsen Ice Shelf should have not undergone significant changes over the past few decades.

An estimation method for InSAR interferometric phase combined with image auto-coregistration

In this paper we propose a method to estimate the InSAR interferometric phase of the steep terrain based on the terrain model of local plane by using the joint subspace projection technique proposed in our previous paper. The method takes advantage of the coherence information of neighboring pixel pairs to auto-coregister the SAR images and employs the projection of the joint signal subspace onto the corresponding joint noise subspace to estimate the terrain interferometric phase. The method can auto-coregister the SAR images and reduce the interferometric phase noise simultaneously. Theoretical analysis and computer simulation results show that the method can provide accurate estimate of the interferometric phase （interferogram） of very steep terrain even if the coregistration error reaches one pixel. The effectiveness of the method is verified via simulated data and real data.

Taiyuan City Subsidence Observed with Persistent Scatterer InSAR

C- and X-bands Synthetic Aperture Radar（SAR） images acquired from February 2009 to September 2010 were processed with Persistent Scatterer Interferometry（PS-InSAR） algorithm to investigate spatial and temporal variations in deformation over Taiyuan City, China. The spatial pattern of subsidence and the magnitude of subsidence rate are similar in the velocity field maps achieved by the algorithm from these two data sets. It shows that there are four primary subsidence centers in Taiyuan City：Xiayuan, Wujiabao, Xiaodian, Sunjiazhai, which are near the groundwater extraction wells. The maximum subsidence rate is up to 70 mm/year at Sunjiazhai. The locus of maximum subsidence has shifted from its historical location in the north to the south. In view of the severe shortage of water resources and presented features of subsidence over Taiyuan City, we inferred that excessive pumping of groundwater was the dominant reason of land subsidence.