Permanent Scatterers Technique Research Articles

A 2D-PRM-Based Atmospheric Phase Correction Method in GB-SAR Interferometry Application

Ground-based synthetic aperture radar (GB-SAR) interferometry has already been recognized as a powerful tool for remote sensing deformation monitoring. However, the accuracy and reliability of the deformation retrieval using GB-SAR instrument is severely affected by atmospheric phase disturbances. In this paper, an improved two-dimentional polynomial regression model (2D-PRM) based atmospheric phase compensation (APC) algorithm, in collaboration with the permanent scatterer (PS) technique, is developed in GB-SAR interferometry. In order to obtain the aliasing-free data required for the APC procedure, an efficient two-stage spatial phase unwrapping method is utilized. Then the reliable PS points are selected by jointly exploiting the amplitude, coherence and amplitude deviation index (ADI) information. After that, the appropriate APC is carried out by virtue of a 2D-PRM based least square (LS) method. Finally, we conduct the atmospheric correction experiments on a real campaign to verify the performance of the proposed scheme.

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.

Repositioning Error Compensation in Discontinuous Ground-Based SAR Monitoring

The discontinuous mode of ground-based synthetic aperture radar (GB-SAR) is suitable for monitoring creep landslides. However, the instrument needs to be installed and disassembled repeatedly, which could inevitably cause repositioning error, and severely affect the accuracy of deformation measurements. This paper performs a detailed theoretical analysis of the repositioning error based on the Taylor expansion of a ternary function, and it can be built as a linear multi-parameter model. Simulations are made to validate the effectiveness of this model compared with two common first-order and second-order models. Then a compensation method based on the permanent scatterer (PS) technique is proposed. Two experiments of discontinuous monitoring are discussed. The first one is an equivalent discontinuous experiment, which utilizes two corner reflectors to evaluate the compensation accuracy. The other one is a discontinuous experiment taken on a steep mountain. Compared with the common methods, the proposed method can better compensate for the error phase and benefit high-precision deformation monitoring.

PS Selection Method for and Application to GB-SAR Monitoring of Dam Deformation

Ground-based synthetic aperture radar (GB-SAR) is a relatively new technique that can be used to monitor the deformation of large-volume targets, such as dams, slopes, and bridges. In this study, the permanent scatterer (PS) technique is used to address the issues encountered in the continuous monitoring of the external deformation of an arch-gravity dam in a hydraulic and hydropower engineering structure in Hubei, China; the technique includes large image data sizes, high accuracy requirements, a susceptibility of the monitoring data to atmospheric disturbances, complex phase unwrapping, and pronounced decoherence. Through an in-depth investigation of PS extraction methods, a combined PS selection (CPSS) method is proposed by fully taking advantage of the signal amplitude and phase information in the monitored scene. The principle and implementation of CPSS are primarily studied. In addition, preliminarily selected PS candidates are directly used to construct and update a triangular irregular network (TIN) to maintain the stability of the subsequent Delaunay TIN. To implement this method, a differential-phase standard-deviation threshold method is proposed to extract PSs that are highly spatially coherent and consistent. Finally, the proposed CPSS was applied to the safety monitoring of the dam. The monitoring results are compared with conventional inverted plumb line monitoring results, and the proposed CPSS is found to be effective and reliable.

A PS processing framework for long-term and real-time GB-SAR monitoring

ABSTRACTBased on the permanent scatterer (PS) technique, deformation measurements were taken in ground-based synthetic aperture radar (GB-SAR) applications. To realize long-term and real-time deformation monitoring, a PS processing framework is proposed. Firstly, a group selection framework is introduced. A certain number of GB-SAR images are selected as a group and different PS sets are selected. Secondly, a fluctuation factor is defined to detect abnormal images. Some images with abnormal amplitude information should not be used for deformation analysis. Thirdly, an adaptive threshold determination method to select the PSs is proposed. The PS numbers in different PS sets can be highly stable. Lastly, a real-time processing framework is introduced which can be applied for on-site monitoring. The proposed processing framework was also used to monitor an open-pit mine for about 11 days. Experimental results validated the effectiveness and reliability of the framework for long-term and real-time GB-SAR monitoring.

Atmospheric phase correction using permanent scatterers in ground-based radar interferometry

Ground-based synthetic aperture radar (GBSAR) is a powerful tool used in monitoring structures such as bridges and dams. However, despite the extremely short range of GBSAR interferometry, the atmospheric effects cannot be neglected. The permanent scatterer (PS) technique is an effective operational tool that utilizes a long series of SAR data and detects information with high accuracy. An algorithm based on the PS technique is developed in accordance with the phase model used in GBSAR interferometry. Atmospheric correction is carried out on a real campaign (Geheyan Dam, China). The atmospheric effects created using this method, which utilizes SAR data, can be effectively reduced compared to when plumb line data are used.

Atmospheric phase screen correction in ground-based SAR with PS technique.

Ground-based synthetic aperture radar (GBSAR) is a powerful tool used in monitoring structures, such as bridges and dams. However, despite the extremely short range of GBSAR interferometry, the atmosphere effects cannot be neglected. The permanent scatterer technique is an effective operational tool that utilizes a long series of SAR data and detects information with high accuracy. An algorithm based on the permanent scatterer technique is developed in accordance with the phase model used in GBSAR interferometry. In this study, atmospheric correction is carried out on a real campaign (Geheyan Dam, China). The atmosphere effects created using this method, which utilizes SAR data, can be reduced effectively compared to when plumb line data are used.

Study of Subsidence detection by DinSAR and evaluation of some factors to the outcome

Study of Subsidence detection by DinSAR and evaluation of some factors to the outcome

Ground Deformation Monitoring in Tongzhou Based on High Resolution SAR Images

D-InSAR technique based on time series of SAR images has been very popular to monitor ground slow deformation in recent years, such as Permanent Scatterers (PS) method, small baseline subsets (SBAS) method, and coherent targets (CT) method. By taking advantage of PS method and CT method, in this paper, small baseline and Permanent Scatterers D-InSAR technique are used to investigate the ground deformation of Tongzhou district in Beijing City, from January 4, 2009 to August 14, 2011 by using 21 COSMO-SkyMed single complex images. The experiment results demonstrate that the two methods of SBAS and PS technique have high consistency in the trends of ground deformation and the time series of deformation value according to choosing some latitude and longitude of the same points, and the deformation rate respectively reaches -7 cm/year and 4 cm/year; during this period, four significant subsidence centers have been developed in Tongzhou district, namely SanJianfang town, Jinzhan town, Songzhuang town and Tongzhou city center. The largest subsidence center is SanJianfang town with an average subsidence rate of −4.7 cm/year, the center of deformation area of SanJianfang town and Tongzhou district are more and more obvious expansion and polymerization. The subsidence of the old center, Wangsiying, has slowed down, and the subsidence in the western region has stopped and some areas even rebounded, and the possible cause for the ground deformation is groundwater extraction.

Estimating deformation due to soil liquefaction in Urayasu city, Japan using permanent scatterers

In Japan, several cities endured severe damage due to soil liquefaction phenomenon, which was developed in association with the massive shaking of the 2011 Tohoku earthquake. Measuring soil liquefaction deformations was not an easy task, mainly because of the total loss of signal coherence in the affected regions. In this paper, we present our approach to estimate the deformations associated with soil liquefaction using interferometric synthetic aperture radar techniques. We use a stack of coseismic interferograms to identify the reliable pixels in the damaged areas using permanent scatterers technique. Then, we estimate and remove the preseismic mean velocity and DEM error components. Finally, we identify the liquefaction deformation component using least squares inversion and spatial phase filtering. We test the performance of the proposed approach using synthetic data, simulating the effects of soil liquefaction. The simulation results show a RMSE of the liquefaction deformation of 5.23mm. After that, we estimate the deformation associated with soil liquefaction in Urayasu city, Japan, using ALOS–PALSAR data. The proposed approach allows a prompt estimation of the liquefaction deformation by utilizing the SAR images archives with only one postseismic SAR image.

Monitoring ground deformation in the settlement of Larissa in Central Greece by implementing SAR interferometry

The settlement of Larissa in the eastern part of Central Greece suffers from continued land deformation as evidenced by ground fissures, sinkholes and subsidence. We used three different interferometric synthetic aperture radar (InSAR) techniques to monitor ground deformation dynamics in the study area. Spatial patterns of short-term changes (35 days) were studied using conventional InSAR, longer-term changes (13 years) by interferometric stacking, and change dynamics of single objects was assessed by permanent scatterer technique. The results indicate co-occurring subsidence and uplift processes in the region with their average annual change rates reaching up to −2.9 and 6.6 mm a−1, respectively. Some of these changes may be attributed to tectonic fault movements, but there are also other mechanisms of continued ground deformation in the region, particularly the swelling and shrinking of expansive soils and human-induced changes in the groundwater level.

A First Approach for Displacement Analysis in Lisbon Downtown Using PS-InSAR

Lisbon Downtown presents unique geomorphologic properties which makes it an area prone to terrain instability. Serious accidents have occurred there, namely, during the 1755 earthquake and a flooding event at the extension of a subway line, demanding a frequent monitorization for safety reasons and expense minimization. In this study, Permanent Scatterers technique is applied. The calculated displacement velocities are compared to those obtained from levelling operations. Possible causes for the discrepancy are presented in the paper. Besides a subsidence trend, a seasonal behaviour is also detected, probably related to aquifer recharge or tides.

Persistent point scatterer statistical analysis for X-band SAR data: the Cosmo-SkyMed case study

This article addresses the problem of characterizing the statistical properties of persistent point scatterers (PPSs) retrieved in a stack of interferometric synthetic aperture radar (SAR) images. The set of parameters are exploited to obtain information about the radiometric response to microwave excitation and to infer some properties related to the physical nature of the targets.The permanent scatterers (PSs) technique is a well-known and worthwhile tool in the field of SAR interferometry and is used to detect terrain deformation with millimetrical accuracy. Although PSs have been adopted in many applications, the physical nature of these targets is still a matter of investigation. A good knowledge of the target properties, such as shape, size, orientation, and roughness, can be a key step for the correct interpretation of the terrain deformation mechanisms and for object identification.PPSs emerge as a subset of PSs that are characterized by a more stringent property; they have an impulsive trend both along and across track directions and sufficient isolation from other strong scatterers. These targets deserve particular attention, since few of them are able, for example, to provide high-precision antenna pattern shape and pointing estimation as well as accurate terrain deformation along the temporal baseline. In this work, the PPS intensity, signal-to-noise ratio (SNR), amplitude dispersion index, and antenna similarity index (a newly defined parameter) are statistically characterized for different kinds of land cover.A stack of images from the Cosmo-SkyMed constellation of satellites are exploited to obtain results for the PPS statistics on four different area typologies: full urban, suburban, vegetated and sparse buildings, and mountains with possible forested areas.

Submillimeter Accuracy of Multipass Corner Reflector Monitoring by PS Technique

This paper presents the results of an experiment that is performed with a network of bidirectional corner reflector (CR) multipass scattering equipment (MUSE), which enable 3-D-displacement measurements. We describe the results of an experiment which was designed to assess the precision of the measurements of ground displacement using MUSE CRs and the permanent scatterer (PS) technique. The CR displacements are applied by micrometric vernier controls during the acquisition of a TerraSAR-X time series of ten images. The relative displacements are estimated between each date, using a PS technique. This paper shows that the relative displacements between the reflectors are estimated with a precision of 0.48 mm along the line of sight. This precision is defined as the standard deviation of the difference between the measured and the applied displacements along the time series. The linear displacement rates of the reflectors are then estimated using the spatiotemporal unwrapping network algorithm, with a 0.4-mm/year precision. We finally show that the experimental results are well predicted by theorical simulations.

Repeat-Pass SAR Interferometry With Partially Coherent Targets

By means of the permanent scatterer (PS) technique, repeated spaceborne synthetic aperture radar (SAR) images with relatively low resolution (about 25 m × 5 m for the European Remote Sensing (ERS) and Envisat satellites) can be used to estimate the displacement (1-mm precision) and 3-D location (1-m precision) of targets that show an unchanged electromagnetic signature. The main drawback of the PS technique is the limited spatial density of targets that behave coherently during the whole observation span (hundreds of PSs per square kilometer in urban site and up to few points in vegetated areas). In this paper, we describe a new approach for multitemporal analysis of SAR images that also allows extracting information from partially coherent targets. The basic idea is to loosen the restrictive conditions imposed by the PS technique. The results obtained in different test sites allowed to increase significantly the spatial coverage of the estimate of height and deformation trend, particularly in extraurban areas.

The Permanent Scatterers Technique with Large Application Potential

The Permanent Scatterers Technique with Large Application Potential

Structural assessment of Mount Etna volcano from Permanent Scatterers analysis

A study of the deformation pattern of Mount Etna volcano based on the results from the Permanent Scatterers (PS) technique is reported. Ground motion data provided by the interferometric synthetic aperture radar (InSAR) PS technique from 1995 to 2000 are compared and validated by GPS data. An analysis of the ascending and descending line of sight (LOS) components of ground velocities has yielded detailed ground deformation maps and cross sections. This analysis allows detection and constraint of discontinuities in the surface velocity field. LOS velocities have then been combined to calculate the vertical and horizontal (E-W) ground velocities. A wide inflation of the edifice has been detected on the western and northern flanks (over an area of about 350 km2). A seaward motion of the eastern and southern flanks has also been measured. PS data allows the geometry and kinematics of the several blocks composing the unstable flanks to be defined even in the highly urbanized areas, and their displacement rates have been measured with millimeter precision. This analysis reveals the extension of some features beyond their field evidences and defines new important features. The results of this work depict a new comprehensive kinematic model of the volcano highlighting the gravitational reorganization of the unbuttressed volcanic pile on its slippery clay basement on the southern flank, but an additional drag force due to a strong subsidence of the continental margin facing the Etna volcano is necessary to explain the PS velocity field observed on the eastern flank.

Recent advances on surface ground deformation measurement by means of repeated space-borne SAR observations

Space-borne Synthetic Aperture Radar interferometry (INSAR) is a well known widely used remote sensing technique to get precise (sub-centimetric) surface deformation measurements on large areas (thousands of km 2 ) and high spatial density of measurement points (hundreds per km 2 ). In this work the recent technological advances of this technique are presented. First, a short review of the INSAR basics is dedicated to readers who are not INSAR specialists. Then, an analysis of the improvement of ground motion measurement offered by multiple repeated space-borne SAR observations gathered by the new generation of high resolution SAR systems is given. An example obtained with the recent German TERRASAR-X system is shown and compared with the measurements obtained with the elder C-band RADARSAT-1 system. Finally, a possible processing of multi-temporal analysis of SAR images that allow extracting ground motion information also from partially coherent targets is given. In this case the core idea is to relax the restrictive conditions imposed by the Permanent Scatterers technique. The results obtained in different test-sites show an increased spatial density of areal deformation trend measurements, especially in extra-urban areas at the cost of missing motions with strong velocity variation.

TIME SERIES RADAR INTERFERMETRY METHOD FOR SURFACE DEFORMATION MONITORING

Surface deformation has become a global problem.The traditional geodetic technique is increasingly proved to be incapable of monitoring the large-scale and serious surface deformation.The new radar interferometry technique provides an effective tool for the large coverage area and a high spatial and temporal resolution for the monitoring.This paper describes the synthetic aperture radar(SAR) interferometry technique for surface deformation monitoring.The time series method based on the permanent scatterers technique is also discussed in detail with Tianjin as a test area.The result of the test shows that the time series method has a very good application value.

Validation of the Submetric Accuracy of Vertical Positioning of PSs in C-Band

The permanent scatterers (PSs) technique is an operational tool in the context of spaceborne synthetic aperture radar interferometry for monitoring the displacement of radar targets with millimetric accuracy. Recently, the target localization capability of the PS technique has been subject of study, and the possibility of generating digital elevation models (DEMs) and digital terrain models (DTMs) by means of the height of a sparse set of points has been evaluated. In this letter, for the first time, the PS height estimate has been validated by exploiting about 250,000 spot heights at street level derived from photogrammetric techniques in the urban area around Milan, Italy. The very high correlation between the two independent measurements confirms the theoretical submetric accuracy of vertical positioning. A multitrack PS DTM has then been generated and compared to the spot heights together with the corresponding Shuttle Radar Topography Mission (SRTM) DEM, showing the very high improvement given by the PS technique to the freely available topographic data. The results have been obtained by processing about 300 European Space Agency (ESA) European Remote Sensing (ERS) satellite and Envisat images acquired from two descending tracks and an ascending one over Milan.