Monitoring Surface Deformation Using Distributed Scatterers InSAR

In the past two decades,extensive and in-depth research has been conducted on Time Series InSAR technology with the advancement of high-performance SAR satellites and the accumulation of big SAR data.The introduction of distributed scatterers in Distributed Scatterers InSAR(DS-InSAR)has significantly expanded the application scenarios of InSAR geodetic measurement by increasing the number of measurement points.This study traces the history of DS-InSAR,presents the definition and characteristics of distributed scatterers,and focuses on exploring the relationships and distinctions among proposed algorithms in two crucial steps:statistically homogeneous pixel selection and phase optimization.Additionally,the latest research progress in this field is tracked and the possible development direction in the future is discussed.Through simulation experiments and two real InSAR case studies,the proposed algorithms are compared and verified,and the advantages of DS-InSAR in deformation measurement practice are demonstrated.This work not only offers insights into current trends and focal points for theoretical research on DS-InSAR but also provides practical cases and guidance for applied research.

Automatic selection of permanent scatterers-based GCPs for refinement and reflattening in InSAR DEM generation

In DEM generation using interferometric synthetic aperture radar(InSAR),the ground control points(GCPs)for refinement and reflattening are usually selected by manual selection,field surveying,GPS points and existing basemaps,which may not be completely suitable for consequent processes.We proposed a new method(auto-PS-GCP)of GCP selection based on permanent scatterers,which automatically defines the thresholds for the coherence,amplitude,and amplitude dispersion index to select permanent scatterer as the GCPs.The GCP thinning(auto-PS-GCP-Thin)was further conducted considering the point density,distances among points and terrain conditions.We used a three-stage assessment that includes:(1)phase stability and intensity of the GCPs,(2)RMSEs of the elevations between GCPs and homonymous points in the reference DEM,and(3)generated DEM accuracy.Three areas respectively in the plain,hilly and mountainous regions were selected to verify the proposed methods.The assessment using both SRTM DEM andICESat-2 points shows that the DEM accuracy of auto-PS-GCP-Thin was improved by 20%∼30%for different areas compared to the manual,where the best DEM accuracy of 4.71 m was found in the plain area.It is concluded that the proposed methods are effective and reliable in various areas with different terrain conditions.

Subsidence Velocity Estimation Using PS-Based Time Series DInSAR

Satellite differential synthetic aperture radar interferometry （DInSAR） has two limitations, i. e. , spatio-temporal decorrelation and atmospheric influence, for the application of regional deformation mapping. This paper proposed a new approach called time series DInSAR based on permanent scatters （PS） to overcome the limitations, and the relevant mathematical model and computing method are also developed. With the proposed algorithm, the experiments were performed to estimate the subsidence velocity field over Shanghai using 26 ERS-1/2 SAR images acquired from 1992 to 2002. The deformation signatures, atmospheric delay and other errors were separated effectively, and the subsidence velocity field over Shanghai was also derived.

Optimum selection of common master image for ground deformation monitoring based on PS-DInSAR technique

Considering the joint effects of various factors such as temporal baseline, spatial baseline, thermal noise, the difference of Doppler centroid frequency and the error of data processing on the interference correlation, an optimum selection method of common master images for ground deformation monitoring based on the permanent scatterer and differential SAR interferometry （PS-DInSAR） technique is proposed, in which the joint correlation coeficient is used as the evaluation function. The principle and realization method of PS-DInSAR technology is introduced, the factors affecting the DInSAR correlation are analysed, and the joint correlation function model and its solution are presented. Finally an experiment for the optimum selection of common master images is performed by using 25 SAR images over Shanghai taken by the ERS-1/2 as test data. The results indicate that the optimum selection method for PS-DInSAR common master images is effective and reliable.

Time series ground subsidence inversion in mining area based on CRInSAR and PSInSAR integration

The subsidence of the mining area was monitored by analyzing the phase of permanent scatters （PS） which maintained high coherence in magnitude of SAR images.A hew method of spatial unwrapping was presented which used the subsidence rates calculated on comer reflector （CR） points as constraints for PS network to perform the spatial unwrapping using the parametric adjustment method.The algorithm achieved the integration of CR data and PSInSAR algorithm.The colliery dense distributed area around Baisha reservoir was chosen as the study area in the experiment.The time series of subsidence from February in 2007 to February in 2010 is successfully inversed by using the periodic function to simulate the linear and nonlinear components of the deformation.The simulation results show that the accuracy can be ± 2.1 mm with the leveling data being used as the external validation data.

Advances in space-borne SAR interferometry and its application to ground deformation monitoring

The development of Differential Synthetic Aperture Radar Interferometry （D-InSAR）, in terms of its evolution from classic to advanced forms, such as Least-Squares approach, Permanent Scatterer Interferometry, Small Baseline Subset, and Coherent Pixel Technique, is reviewed, describing concisely the main principles of each method and highlighting the difference and relationship between them. Applications of InSAR technology in China were then introduced, together with the obstacles to overcome and feasible strategies, such as integrating MERIS/MODIS data to compensate for the atmospheric effect and GPS, and multi-platform SAR data to make InSAR technique practical and operational under various conditions. The latest devel- opments were then analyzed along with high-quality SAR data, available thanks to the newly launched high-tech satellites, TerraSAR-X, and Cosmo Sky-med, and conclusions were drawn about the main limitations of the technique.

基于时序InSAR的上海市地面沉降时空演变特征分析

基于2018-06—2019-10期间的17景Sentinel-1A影像数据,采用永久散射体合成孔径雷达干涉测量(permanent scatterer interferometric synthetic aperture radar,PS‐InSAR)技术研究了上海市的地面沉降时空演变特征,获得了上海市该时间段内的平均沉降速率场、沉降时间序列及累计沉降量,并分析了该地区的地面沉降时空演变特征与降水量、城市化进程等因素的关联关系。结果表明:①在研究时段内,上海市不均匀沉降明显,沉降最严重的区域位于松江区邱泾村,沉降速率范围为-18.3~-14.2 mm/a;此外,金山区南星桥附近也出现较为明显的沉降现象,最大累计沉降量达-23 mm。②上海市北部出现大范围沉降,地区平均沉降速率在-11~-4 mm/a间。西部及西南部也出现大范围沉降现象,并出现明显的沉降漏斗,沉降较为严重,而东部地区地面呈现抬升现象。③研究区域地面沉降的季节性变化与降水量有关;城市化进程与地面沉降存在一定的空间相关性。

Ground infrastructure monitoring in coastal areas usingtime-series inSAR technology:the case study of Pudong International Airport,Shanghai

Shanghai Pudong International Airport(PDIA),with its east side built along the coast with weak geological conditions,is prone to uneven foundation settlement due to the consolidation and compression of soil and erosion of coastal tides,affecting the safe operation of the airport.Therefore,it is crucial to conduct dynamic subsidence monitoring within the airport,especially in the runway area.29 scenes of ascending track Sentinel-1A radar images from August 2016 to June 2018 are selected to perform surface deformation inversion based on PS-InSAR and improved SBAS-InSAR for PDIA and its around coastal area.Through cross-validation,the reliability of the time-series InSAR technique for dynamic monitoring of surface deformation of coastal zone infrastructures is confirmed.The results show severely uneven settlement.By combining the monitoring results with the local geological and hydrological dataset,the driving factors of differential deformation of the infrastructures are analyzed,including stratigraphic geological conditions,ground loadings,foundation treatment methods,water erosion,and groundwater level changes.Finally,the time-series deformation characteristics and the causes of PDIA’s runway are emphasized based on the PS deformation results.This case provides a reference for the safety management of critical infrastructure in coastal areas using advanced InSAR technique.

Three Gorges Dam stability monitoring with time-series InSAR image analysis

In this paper,we carried out a combination of permanent scatterer and quasi permanent scatterer time-series InSAR image analyses to extract geometric information over the area of the Three Gorges Dam.For the first time,we measured and analyzed the deformation of the Three Gorges Dam and its surrounding area using 40 SAR images acquired from 2003 to 2008.Our results indicate that the temporal deformation of the left part of the dam has ceased and that the deformation of the dam was influenced by the changing level of the Yangtze River.Seasonal deformation due to varying temperature is also observed.The obtained results agree well with the published results of the Three Gorges Dam deformation obtained by employing conventional survey methods.We also found that there is an area of abnormal subsidence near Zigui County.This paper demonstrates the potential of time-series InSAR image analysis in the monitoring of dam stability and measurement of subsidence.

PS-InSAR与PSP-InSAR监测地面沉降的比较

针对覆盖杭州地区的36景COSMO-SkyMed影像,采用永久散射体合成孔径雷达干涉测量(permanent scatterer interferometric synthetic aperture radar,PS-InSAR)技术和永久散射体对合成孔径雷达干涉测量(permanent scatterer pair InSAR,PSP-InSAR)技术进行数据处理,获取研究区域的两组地面沉降信息,并对两组结果进行交叉验证。结果表明,两种技术获取的结果无论是在沉降空间分布还是在沉降量级上,都保持高度的一致性,证明两种技术获得的结果都是可靠的。