Permanent Scatterers Research Articles

Multi-Temporal InSAR Deformation Monitoring Zongling Landslide Group in Guizhou Province Based on the Adaptive Network Method

Due to the influence of atmospheric phase delays and terrain fluctuation in complex mountainous areas, traditional PS-InSAR technology often fails to select enough measurement points (MPs) and loses effective MPs during phase unwrapping. To solve this problem, this paper proposes an adaptive network construction algorithm, which combines the permanent scatterer (PS) points with the distributed scatterer (DS) points. Firstly, to ensure the extraction quality of the DS points, the covariance matrix of DS points is estimated robustly. Secondly, based on the traditional Delaunay triangulation network, an adaptive network construction method is proposed, which can adaptively increase edge redundancy and network connectivity by considering the edge length, edge coherence, edge number, and spatial distribution. Finally, a total of 31 RADARSAT-2 SAR images that cover the Zongling landslide group in Guizhou Province were used to prove the effectiveness of proposed method. The results show that the quantity of available DS points can be increased by 23.6%, through the robust estimation of the covariance matrix. In addition, it is demonstrated that the proposed network construction algorithm can balance the number, distribution, and quality of edges in the dense and sparse areas of MPs adaptively. This adaptive network construction approach can maintain good connectivity and avoid losing effective MPs to the greatest extent, especially when the scattering points are far away from the reference points. In short, the proposed algorithm improves the number of effective MPs and accuracy of phase unwrapping.

A simplified procedure to assess uncertainties in the estimation of the rigid motion of isolated buildings based on InSAR monitoring

This paper proposes a method to monitor the rigid motion of isolated buildings based on DInSAR technology. The satellite monitoring of isolated buildings is made possible by both the availability of high resolution data thanks to the current generation of SAR constellations and the combination of measurements from dual orbits. However, to assess whether the accuracy of the estimated motion is enough for structural monitoring purposes, the uncertainties of the estimated motion components need to be evaluated as well. To this aim, an analytical procedure to evaluate the estimated parameter uncertainties is also proposed. The proposed procedure is based on the simplifying assumption that the rigid motion components are independent of each other. The performance of the presented analytical procedure is investigated by comparing the analytical uncertainties to those obtained from numerical simulations, performed accounting for the uncertainties affecting SAR data. These last are related to the measurement uncertainties and errors in the positioning of the permanent scatterers.

Maden Sahalarında Köşe Reflektör (CR) Tesisi ve Sabit Saçıcı (PS) Kontrolü

Deformations in mining areas have been started to be monitored by satellite SAR-based methods, which have recently emerged as an alternative to classical methods (GNSS receivers, Geometric Leveling, Terrestrial Lidar, UAV Photogrammetry, etc.). The most important advantage of this method is that quite wide areas can be monitored remotely. However, the mentioned way also has some disadvantages. The first of these; deformations can only be determined in the direction of the Satellite Line Of Sight (LOS), and the second one is that there is no correlated reflective surface due to the continuous change of topography in the locations where mining activities are carried out. Within the framework of this study, it is aimed to monitor PS by placing corner reflectors (CR) in the locations where sufficient Permanent Scatterer (PS) cannot be produced in Kalburçayırı and Hamal Coal Fields of Kangal Thermal Reactor Elektric production A.Ş. By considering the area through Sentinel-1A/B satellites, new PSs constituted by employing the CR facility has been successfully observed in locations, where PS could not be produced before. The results show us that; placing corner reflectors in locations where sufficient PS cannot be made or not determined at all, increases the number and quality of PS positively.

Submillimeter-spatial-resolution φ-OFDR strain sensor using femtosecond laser induced permanent scatters.

A φ-optical frequency domain reflectometry (OFDR) strain sensor with a submillimeter-spatial-resolution of 233 µm is demonstrated by using femtosecond laser induced permanent scatters (PSs) in a standard single-mode fiber (SMF). The PSs-inscribed SMF, i.e., strain sensor, with an interval of 233 µm exhibited a Rayleigh backscattering intensity (RBS) enhancement of 26 dB and insertion loss of 0.6 dB. A novel, to the best of our knowledge, method, i.e., PSs-assisted φ-OFDR, was proposed to demodulate the strain distribution based on the extracted phase difference of P- and S-polarized RBS signal. The maximum measurable strain was up to 1400 µε at a spatial resolution of 233 µm.

Landslide Detection and Mapping Based on SBAS-InSAR and PS-InSAR: A Case Study in Gongjue County, Tibet, China

The rock mass along the Jinsha River is relatively broken under complex geological action. Many ancient landslides were distributed along the Jinsha River in Gongjue County, which is very dangerous under the action of gravity, tectonic stress and river erosion. Efficient and accurate identification and monitoring of landslides is important for disaster monitoring and early warning. Interferometric synthetic aperture radar (InSAR) technology has been proved to be an effective technology for landslide hazard identification and mapping. However, great uncertainty inevitably exists due to the single deformation observation method, resulting in wrong judgment during the process of landslide detection. Therefore, to address the uncertainties arising from single observations, a cross-comparison method is put forward using SBAS-InSAR (small baseline subset InSAR) and PS-InSAR (permanent scatterers InSAR) technology. Comparative analysis of the spatial complementarity of interference points and temporal deformation refined the deformation characteristics and verified the reliability of the InSAR results, aiding in the comprehensive identification and further mapping of landslides. Landslides along the Jinsha River in Gongjue County were studied in this paper. Firstly, 14 landslides with a total area of 20 km2 were identified by using two time-series InSAR methods. Then, the deformation characteristics of these landslides were validated by UAV (unmanned aerial vehicle) images, multiresource remote sensing data and field investigation. Further, the precipitation data were introduced to analyze the temporal deformation characteristics of two large landslides. Lastly, the influence of fault activity on landslide formation is further discussed. Our results demonstrate that the cross-comparison of the time-series InSAR method can effectively verify the accuracy of landslide identification.

Correlating severe land subsidence and confined brine aquifer compaction in the Yellow River Delta, China, with Sentinel-1A/1B satellite images

In recent years, noticeable subsidence depressions have occurred along the coastal zone of the Yellow River Delta. In some coastal areas, the average annual subsidence varies from tens of millimeters to hundreds of millimeters. Although some studies have discovered a significant land subsidence funnel in the coastal zone of the Yellow River Delta, it has rarely been reported in recent years. Using Sentinel-1A/1B images from the last five years and permanent scatterers interferometric synthetic aperture radar technology, we found a typical subsidence bowl in the northeastern part of the delta, with a cumulative settlement of nearly 1 m over five years. In addition, we used the approach of soil mechanics to simulate the settlement of confined brine layers with different thicknesses under drainage conditions. We found that the 15 m thick confined aquifer can produce 1 m of settlement for every 15% decrease in water content. The simulation results explain the large settlement of the brine industrial area. This study can provide guidance for brine mining in the future. If we continue to overexploit underground brine, there will be more severe land subsidence in the delta in the future.

Land deformation monitoring in the Taiyuan area based on PS-InSAR.

Land subsidence problems have become increasingly prominent. Traditional monitoring methods, such as level measurements, have high costs and low efficiency. Permanent scatterer interferometric synthetic aperture radar (PS-InSAR) has several advantages for land subsidence monitoring based on technological innovations. Aimed at resolving the key problems associated with PS-InSAR technology, the accuracy of three external digital elevations models (DEMs, namely, SRTM, ASTER GDEM, and PleiadesDEM) was analysed and compared. We found that the introduction of ground control points can significantly improve the elevation accuracy of DEMs. Herein, we introduce the specific processing steps and selection of the key parameters for IN-SAR data using the StaMPS software. We discuss the differences between IN-SAR technology and levelling measurements as well as the influence that the different external DEMs have on IN-SAR data. Based on 36 scenes of TerraSAR-X images, we obtained results for land deformation monitoring in Taiyuan City using PS-InSAR technology, which provided satisfactory monitoring results.

Research on time series InSAR monitoring method for multiple types of surface deformation in mining area

Interferometric Synthetic Aperture Radar (InSAR) has become the primary remote sensing detection method for monitoring significant surface subsidence and deformation caused by underground coal mining. Time Series InSAR has been intensively researched in mining-caused deformation monitoring for its ability to provide surface deformation time series, with Small Baseline Subset InSAR (SBAS-InSAR) and Permanent Scatter InSAR (PS-InSAR) being two classical methods. To obtain the incline and curvature in mining areas and assess the building damage, this paper exploits the SBAS-InSAR and PS-InSAR techniques to estimate surface incline and curvature, following the principle of directional derivatives. The surface beneath the villages and the industrial square near the 7221 Grout-filled working face in the Huaibei mining area of Anhui Province, China, was analyzed. The estimated surface incline and curvature with SBAS-InSAR were within the threshold values specified for Class I damage, while PS-InSAR showed <1% of measurements that exceeded this threshold. This paper provides a method for monitoring the surface deformation beneath the buildings in the mine area. Meanwhile, the dynamic analysis of the damaged buildings provides a basis for determining the influence range with grout-filled working faces.

Land Subsidence Monitoring Method in Regions of Variable Radar Reflection Characteristics by Integrating PS-InSAR and SBAS-InSAR Techniques

In the InSAR solution, the uneven distribution of permanent scatterer candidates (PSCs) or slowly decoherent filtering phase (SDFP) pixel density in a region of variable radar reflection feature can cause local low accuracy in single interferometry. PSCs with higher-order coherence in Permanent Scatter InSAR (PS-InSAR) are generally distributed in those point targets of urban built-up areas, and SDFP pixels in Small Baseline Subset InSAR (SBAS-InSAR) are generally distributed in those distributed targets of countryside vegetation areas. According to the respective reliability of PS-InSAR and SBAS-InSAR for different radar reflection features, a new land subsidence monitoring method is proposed, which combines PS-SBAS InSAR by data fusion of different interferometry in different radar reflection regions. Density-based spatial clustering of applications with noise (DBSCAN) clustering analysis is carried out on the density of PSCs with higher-order coherence in PS-InSAR processing to zone the region of variable radar reflection features for acquiring the boundary of data fusion. The vector monitoring data of PS-InSAR is retained in the dense region of PSCs with higher-order coherence, and the vector monitoring data of SBAS-InSAR is used in the sparse region of PSCs with higher-order coherence. The vertical displacements from PS-InSAR and SBAS-InSAR are integrated to obtain the optimal land subsidence. The verification case of 38 SAR images acquired by the Sentinel-1A in Suzhou city indicates that the proposed method can automatically choose a matched interferometry technique according to the variability of radar reflection features in the region and improve the accuracy of using a single interferometry method. The integrated method of the combined field is more representative of overall subsidence characteristics than the PS-InSAR-only or SBAS-InSAR-only results, and it is better suited for the assessment of the impact of land subsidence over the study area. The research results of this paper can provide a useful comprehensive reference for city planning and help decrease land subsidence in Suzhou.

QUALITY INSPECTION OF SURFACE DEFORMATION MONITORING RESULTS BASED ON PS-INSAR TECHNOLOGY

Abstract. In view of the problems that the permanent scatterer synthetic aperture radar interferometry (PS-InSAR) technology was limited by the difference of processing algorithms and the professional level of data processing personnel, and its monitoring results were still difficult to fully achieve the theoretical accuracy, a new technical process suitable for the detection of PS-InSAR surface deformation monitoring results was proposed in this paper. Based on the analysis of the characteristics of monitoring results, the inspection work was carried out by means of overall inspection. The test parameters, test objects and test items to be tested, as well as the test methods of different test parameters were determined; The key links of PS-InSAR surface deformation monitoring data processing were analyzed in detail, and the technical flow of mathematical accuracy detection was given. Finally, the quality detection of surface deformation monitoring results based on PS-InSAR technology of 3000 square kilometres were carried out, the results showed that the proposed technical route was feasible and quality evaluation result was objective.

Monitoring and Analysis of Ground Surface Settlement in Mining Clusters by SBAS-InSAR Technology.

In this paper, we use the small baseline set technology and the early geological hazard identification method based on the selection of Permanent Scatter (PS) and Distributed Scatter (DS) points to carry out the research on surface deformation monitoring caused by underground activities in mining cluster areas. We adopted the Small Baseline Subset InSAR (SBAS-InSAR) technique to process Sentinel-1A SAR images over the research area from March 2017 to May 2021. The deformation estimation technology based on the robustness of PS points and DS points can be used for early identification of high-density surface subsidence in a large area of mines. The surface subsidence information can be obtained quickly and accurately, and the advantages of using InSAR technology to monitor long-time surface subsidence in complex mining cluster areas was explored in this study. By comparing the monitoring data of the Global Navigation Satellite System (GNSS) ground monitoring equipment, the accuracy error of large-scale surface settlement information is controlled within 8 mm, which has high accuracy. Meanwhile, according to the spatial characteristics of cluster mining areas, it is analyzed that the relationship between adjacent mining areas through groundwater easily leads to regional associated large-area settlement changes. Compared with the D-InSAR (Differential InSAR) technology applied in mine monitoring at the early stage, this proposed method can monitor a large range of long time series and optimize the problem of decoherence to some extent in mining cluster areas. It has important reference significance for early monitoring and early warning of subsidence disaster evolution in mining intensive areas.

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

ABSTRACT 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.

Spatiotemporal Visualisation of PS InSAR Generated Space–Time Series Describing Large Areal Land Deformations Using Diagram Map with Spiral Graph

The space–time series carry information on temporal and spatial patterns in observed phenomena. The reported research integrates computational, visual and cartographic methods to support visual analysis of space–time series describing terrain surface movement. The proposed methodology for space–time series visualisation can support their analysts in investigating space–time patterns using transformation, clustering, filtration and visualisation. The presented approach involves spiral graphs for representation time dimension and cartographic visualisation through proportional point symbol map for representation of spatial dimension. The result is an intuitive visualisation of space–time series, conveying the sought-after spatio-temporal information. For practical tests, we used space–time series obtained by permanent scatterers interferometry (PS InSAR) to monitor the Earth’s surface movement above the underground gas storage (UGS) Tvrdonice, the Czech Republic. An UGS is characterised by periodic injection and withdrawal of natural gas, which induces periodic movement of the terrain above it. We have verified that our visualisation method provides the required pattern information and is easy to use.

Research on a GB-SAR interferogram filtering method for open-pit mines based on eight-neighbourhood outlier discrimination

Ground-based synthetic aperture radar (GB-SAR) interferograms contain a large amount of phase noise. The existing methods lose effective deformation information to varying degrees upon filtering, which seriously reduces the monitoring accuracy of GB-SAR. In this paper, a GB-SAR interferogram filtering method for open-pit mines is studied. First, permanent scatterer points (PSPs) are extracted through coarse filtering, and the distribution of the noise phase is analysed. Then, an improved Grubbs outlier discrimination criterion is introduced considering the uncertainty of the PSP distribution. A method based on the eight-neighbourhood outlier discrimination (EOD) criterion is proposed to identify noise points. High-coherence points (HCPs) are used to reconstruct the phase of the noise points to filter the GB-SAR interferogram. Finally, the filtering effect is quantitatively evaluated using the peak signal-to-noise ratio (PSNR) and structural similarity (SSIM). The superiority of the proposed filtering method in the image displacement region is verified based on simulated and real deformation data. The results show that the proposed method can accurately filter out the phase noise of interferograms and improve the accuracy of GB-SAR for slope monitoring.

Monitoring of large and inconsistent deformation in coal mining area using point-like target offset tracking

ABSTRACT Ground deformation in the coal mining area of Northwestern China is usually featured by large and inconsistent subsidence. Large subsidence brings great challenge to Differential Interferometric Synthetic Aperture Radar (DInSAR) and Permanent Scatterer Interferometry (PSI) technology due to the pixel-level offset in the range direction after co-registration, which could directly result in complete coherence loss even for the artificial Corner Reflectors (CRs). Offset tracking provides an alternative to capture the large deformation although the results could be biased due to the large deformation gradient and use of fixed correlation window size. In this paper, the point-like target (PT) offset tracking method is introduced to deformation monitoring in coal mining area with a levelly decreasing correlation window size. For each PT-centered SLC patch in the reference SAR image, the estimate from the larger correlation window will serve as a guide for the smaller one to locate the matching SLC patch in the slave SAR image, thus providing a guarantee that the residual offsets to be estimated remain to be a small fraction of the decreasing patch size. The offset estimates were evaluated by ground surveying results at 34 CRs obtained using single reference real-time kinematic (RTK) GPS technique, with a RMS error of 1/13-1/14 SLC pixel in both the range and azimuth directions.

Quantifying vertical land motion at tide gauge sites using permanent scatterer interferometric synthetic aperture radar and global navigation satellite system solutions

Quantifying vertical land motion at tide gauge sites using permanent scatterer interferometric synthetic aperture radar and global navigation satellite system solutions

Increasing spatial coverage in rough terrain and vegetated areas using InSAR optimized pixel selection: application to Tohoku, Japan

ABSTRACT One of the major limitations of using Interferometric Synthetic Aperture Radar (InSAR) in time series analysis is the low-phase coherence associated with rough terrain and vegetated areas, which results in limited spatial coverage in such regions. Permanent scatterers technique was introduced to overcome this limitation using time-series analysis. However, identifying major scatterers within a pixel requires the single-looked pixels oversampling which can be a demanding process especially with large interferometric stacks and vast study areas. Therefore, using multilooked temporal coherent pixels was proposed to increase processing efficiency and coverage by utilizing distributed targets, but this technique may exclude pixels with reliable phase returns because of their temporal varying neighboring pixels. In this paper, we propose a technique to identify multilooked temporal stable pixels with reliable phase returns independent of their neighboring pixels. We conduct a simulation analysis to relate the spatial coherence of a pixel with its expected temporal correlation in the time series analysis module. We found that a liberal temporal correlation threshold of 0.53 in multilooked pixels stack is equivalent to a spatial coherence threshold of 0.2 when using number of looks of 9, which is considered acceptable in temporal coherent pixels, in terms of phase standard deviation. Applying these findings to study the 2011 Tohoku earthquake in the northeastern part of Japan resulted in increasing the number of usable pixels and spatial coverage index by nearly 50.4% and 36.8%, respectively, compared to the temporal coherent pixels. Furthermore, we propose an approach to integrate GPS observations with InSAR time series analysis, which resulted in deformation maps of the megathrust 2011 Tohoku earthquake with mean RMSE of 11.4 mm and a correlation of 98% in comparison to GPS observations.

Estimation of Spouted Hot Mudflow Current Using Continuity Equation and DInSAR

Several techniques have been proposed to observe long-term land surface deformation using phase information of synthetic aperture radar (SAR), for example, interferometric SAR (InSAR), differential interferometric SAR (DInSAR), permanent scatterer interferometric SAR (PS-InSAR), and small baseline subset (SBAS) using images of JERS-1, ALOS-1/2, ENVISAT, ERS-1/2, RADARSAT-1/2, TerraSAR-X, SENTINEL-1A/B, and so on. These methods have also been employed to investigate land deformation and the impact caused by the hot mudflow accident at the study area of regency of Sidoarjo, East Java province, Indonesia, where this disaster happened on May 29, 2006, and has been flowing until now. But these methods only derived the land surface deformation and did not figure geological situation in the Earth, especially the current of geological material outflow. Therefore, this research proposed the continuity equation of the law of conservation of material to estimate the current of material outflow to investigate the impact of the land surface disaster in the study area. The information of vertical deformation or subsidence is derived by the consecutive DInSAR using multispaceborne SAR and substituted into the proposed equation to estimate the volume and current of hot mud outflow. The differential global positioning system (GPS) data collected since 2006 were employed to validate the analysis result of land surface deformation, and the root means square (rms) error is 0.46 m. The result obtained the current at the center of the study area at the beginning of the mudflow period was 6800 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /day and decreased from 2018 until now that matched well with the local reports. The proposed equation could also be applied for observation of land deformation, volcano, fault activity, underground water, and so on, using remote sensing technologies.

Monitoring of the ground deformation in Penang Island, Malaysia using Permanent Scatterer Interferometry Synthetic Aperture Radar (PS-InSAR) and Ground-Penetrating Radar (GPR) techniques

round deformations (e.g., landslide and subsidence) have substantially risen recently around Penang Island, Malaysia. The development of hillslopes for rapid urbanisation and heavy rainfall has detrimental impacts on Penang Island soil layers. Modelling, simulation, and the development of susceptibility maps were past methods used to predict potential ground deformations of Penang Island. There is no published work on the Interferometry Synthetic Aperture Radar (InSAR) technique, where ground deformation of the region has been holistically studied. This work integrates the Persistent Scatterer InSAR (PS-InSAR) technique with Ground Penetrating Radar (GPR) to monitor the deformation on the island and identify possible subsurface causes for the disturbance. Twenty-four descending Sentinel-1A datasets acquired between 14th July 2017 and 13th October 2018 were processed to monitor and map ground deformation areas with a focus on three selected regions- Batu Feringghi (BF), Paya Terubong (PT), and Tanjung Bungah (TB), where multiple landslides occurred between 2017 and 2018. InSAR results were later analysed using the Statistical Package for the Social Sciences (SPSS) tool and validated by the available Global Positioning System (GPS) analysis. InSAR analyses reveal the mean deformation values of -3.13 mm/yr, -2.76 mm/yr and -4.77 mm/yr for the BF, PT, and TB areas. GPR surveys were conducted with a 300/800 MHz dual-frequency antenna at the three selected study areas. Anomalies (wall cracks, road fissures, cavities, drains, and pipes) detected using GPR profiles correlated well with the permanent scatterer points calculated using the InSAR technique.

Performance Assessment of InSAR-Based Vertical Displacement Monitoring of Sluices in Coastal Soft Soil Area

Sluices are main flood control infrastructures in coastal areas, where soft rock and soft soil are widely distributed. In soft soil areas, the vertical displacement of sluice is common, which is the main factor affecting the sluice safety. So, it is very important for sluice safety control according to the prototypical observations on deformation. Considering some drawbacks of leveling, such as it can only provide a limited number of points and requires time-consuming field work, this paper evaluates the performance of Interferometric Synthetic Aperture Radar (InSAR)-based method in monitoring long-term vertical displacement deformations of sluices. Taking 12 sluices in Northern Jiangsu, China as an example, 129 Sentinel-1 C-band VV-polarizatio ascending SAR images that span the period from April 2015 to January 2020 were used to monitor their vertical displacement deformations. The leveling results are made to verify the accuracy and reliability of Permanent Scatterer InSAR (PSInSAR) method. The validation indicates good agreement between PSInSAR results and leveling results. Considering the higher accuracy of leveling, PSInSAR method is more suitable as an auxiliary technology besides leveling method to focus on the early warning of sluice deformation risk events.