Permanent scatterers in SAR interferometry
TL;DR: The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images.
Abstract: Temporal and geometrical decorrelation often prevents SAR interferometry from being an operational tool for surface deformation monitoring and topographic profile reconstruction. Moreover, atmospheric disturbances can strongly compromise the accuracy of the results. The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images. When, as it often happens, the dimension of the PS is smaller than the resolution cell, the coherence is good even for interferograms with baselines larger than the decorrelation one, and all the available images of the ESA ERS data set can be successfully exploited. On these pixels, submeter DEM accuracy and millimetric terrain motion detection can be achieved, since atmospheric phase screen (APS) contributions can be estimated and removed. Examples are then shown of small motion measurements, DEM refinement, and APS estimation and removal in the case of a sliding area in Ancona, Italy. ERS data have been used.
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TL;DR: Results obtained on the data acquired from 1992 to 2000 by the European Remote Sensing satellites and relative to the Campi Flegrei caldera and to the city of Naples, Italy, that demonstrate the capability of the proposed approach to follow the dynamics of the detected deformations.
Abstract: We present a new differential synthetic aperture radar (SAR) interferometry algorithm for monitoring the temporal evolution of surface deformations. The presented technique is based on an appropriate combination of differential interferograms produced by data pairs characterized by a small orbital separation (baseline) in order to limit the spatial decorrelation phenomena. The application of the singular value decomposition method allows us to easily "link" independent SAR acquisition datasets, separated by large baselines, thus increasing the observation temporal sampling rate. The availability of both spatial and temporal information in the processed data is used to identify and filter out atmospheric phase artifacts. We present results obtained on the data acquired from 1992 to 2000 by the European Remote Sensing satellites and relative to the Campi Flegrei caldera and to the city of Naples, Italy, that demonstrate the capability of the proposed approach to follow the dynamics of the detected deformations.
3,522 citations
Cites background or methods from "Permanent scatterers in SAR interfe..."
...Additionally, an atmospheric phase artifacts filtering operation is carried out on the computed space–time deformation measurements following the lines of the solution developed for the PS technique [16], [17]; in our case, the filtering operation takes benefit from the high spatial density of the imaged pixels....
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...In this case, the applied filtering operation is derived from the PS approach discussed in [16] and [17], which is based on the observation that the atmospheric signal phase component is characterized by a high spatial correlation but exhibits a significantly low temporal correlation....
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...Moreover, a new solution for maximizing the number of acquisitions used has been proposed, and the technique is referred to as permanent scatterers (PS) [16], [17]....
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TL;DR: In this article, a new approach to the estimation of the atmospheric phase contributions, and the local displacement field is proposed based on simple statistical assumptions, is presented in order to cope with nonlinear motion of the targets.
Abstract: Discrete and temporarily stable natural reflectors or permanent scatterers (PS) can be identified from long temporal series of interferometric SAR images even with baselines larger than the so-called critical baseline. This subset of image pixels can be exploited successfully for high accuracy differential measurements. The authors discuss the use of PS in urban areas, like Pomona, CA, showing subsidence and absidence effects. A new approach to the estimation of the atmospheric phase contributions, and the local displacement field is proposed based on simple statistical assumptions. New solutions are presented in order to cope with nonlinear motion of the targets.
1,901 citations
TL;DR: This paper provides first a tutorial about the SAR principles and theory, followed by an overview of established techniques like polarimetry, interferometry and differential interferometric as well as of emerging techniques (e.g., polarimetric SARinterferometry, tomography and holographic tomography).
Abstract: Synthetic Aperture Radar (SAR) has been widely used for Earth remote sensing for more than 30 years. It provides high-resolution, day-and-night and weather-independent images for a multitude of applications ranging from geoscience and climate change research, environmental and Earth system monitoring, 2-D and 3-D mapping, change detection, 4-D mapping (space and time), security-related applications up to planetary exploration. With the advances in radar technology and geo/bio-physical parameter inversion modeling in the 90s, using data from several airborne and spaceborne systems, a paradigm shift occurred from the development driven by the technology push to the user demand pull. Today, more than 15 spaceborne SAR systems are being operated for innumerous applications. This paper provides first a tutorial about the SAR principles and theory, followed by an overview of established techniques like polarimetry, interferometry and differential interferometry as well as of emerging techniques (e.g., polarimetric SAR interferometry, tomography and holographic tomography). Several application examples including the associated parameter inversion modeling are provided for each case. The paper also describes innovative technologies and concepts like digital beamforming, Multiple-Input Multiple-Output (MIMO) and bi- and multi-static configurations which are suitable means to fulfill the increasing user requirements. The paper concludes with a vision for SAR remote sensing.
1,614 citations
Cites methods from "Permanent scatterers in SAR interfe..."
...A further milestone in the SAR development was associated to differential SAR interferometry with permanent scatterers (PS) for subsidence monitoring [17], a technique that was developed using data from ERS-1/2 and later ENVISAT/ASAR (C-band)....
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TL;DR: This paper introduces a new approach, SqueeSAR, to jointly process PS and DS, taking into account their different statistical behavior, and results on real SAR data, acquired over an Alpine area, confirm the effectiveness of this new approach.
Abstract: Permanent Scatterer SAR Interferometry (PSInSAR) aims to identify coherent radar targets exhibiting high phase stability over the entire observation time period. These targets often correspond to point-wise, man-made objects widely available over a city, but less present in non-urban areas. To overcome the limits of PSInSAR, analysis of interferometric data-stacks should aim at extracting geophysical parameters not only from point-wise deterministic objects (i.e., PS), but also from distributed scatterers (DS). Rather than developing hybrid processing chains where two or more algorithms are applied to the same data-stack, and results are then combined, in this paper we introduce a new approach, SqueeSAR, to jointly process PS and DS, taking into account their different statistical behavior. As it will be shown, PS and DS can be jointly processed without the need for significant changes to the traditional PSInSAR processing chain and without the need to unwrap hundreds of interferograms, provided that the coherence matrix associated with each DS is properly “squeezed” to provide a vector of optimum (wrapped) phase values. Results on real SAR data, acquired over an Alpine area, challenging for any InSAR analysis, confirm the effectiveness of this new approach.
1,324 citations
Cites methods from "Permanent scatterers in SAR interfe..."
...…data vectors rather than complex reflectivity values, and following the conventional PS approach where the statistics of amplitude data is used as a proxy for phase stability [4], the test is applied to vectors of amplitude values of radar reflectivity, rather than to real and/or imaginary parts....
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TL;DR: In this paper, the authors presented results obtained using 45 ERS SAR images gathered over the Italian town of Camaiore (within a time span of more than 6 years and a range of normal baseline of over 2000 m) are presented.
Abstract: Differential SAR interferometry measurements provide a unique tool for low-cost, large-coverage surface deformations monitoring. Limitations are essentially due to temporal decorrelation and atmospheric inhomogeneities. Though temporal decorrelation and atmospheric disturbances strongly affect interferogram quality, reliable deformation measurements can be obtained in a multi-image framework on a small subset of image pixels, corresponding to stable areas. These points, hereafter called Permanent Scatterers, can be used as a `natural GPS network' to monitor terrain motion, analyzing the phase history of each one. In this paper, results obtained using 45 ERS SAR images gathered over the Italian town of Camaiore (within a time span of more than 6 years and a range of normal baseline of more than 2000 m) are presented. The area is of high geophysical interest because it is known to be unstable. A subterranean cavity collapsed in October 1995 causing the ruin of several houses in that location. Time series analysis of the phase values showed the presence of precursors three months before the collapse.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
1,320 citations
Cites background from "Permanent scatterers in SAR interfe..."
...It is well known that a pixel in a SAR image changes its phase due to: (1) the relative position satellite-scatterer; (2) possible temporal changes of the target; (3) the effect of the atmosphere....
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...øi =p(T,)+C1 •E (3) where is the DEM error and C, is proportional to B1....
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References
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6,899 citations
Book•
01 Jan 1979
TL;DR: An electromagnetic pulse counter having successively operable, contact-operating armatures that are movable to a rest position, an intermediate position and an active position between the main pole and the secondary pole of a magnetic circuit.
Abstract: An electromagnetic pulse counter having successively operable, contact-operating armatures. The armatures are movable to a rest position, an intermediate position and an active position between the main pole and the secondary pole of a magnetic circuit.
4,897 citations
"Permanent scatterers in SAR interfe..." refers background or methods in this paper
...We then consider a complex circular gaussian noise characterized by a power for both real ( ) and imaginary components ( ). The distribution of the amplitude values is given by the Rice distribution [ 18 ]...
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...For low SNR, the dispersion index tends to the value proper for the Rayleigh distribution ( 0.5 [ 18 ]), while small values of are good estimates of the phase dispersion....
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TL;DR: It is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible and such a technique could provide a global digital terrain map.
Abstract: A radar interferometric technique for topographic mapping of surfaces, implemented utilizing a single synthetic aperture radar (SAR) system in a nearly repeating orbit, is discussed. The authors characterize the various sources contributing to the echo correlation statistics, and isolate the term which most closely describes surficial change. They then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time. It is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible. The authors present such a map of a forested area in Oregon which also includes some nearly unvegetated lava flows. Such a technique could provide a global digital terrain map. >
2,167 citations
"Permanent scatterers in SAR interfe..." refers background in this paper
...smaller than the resolution cell would allow reliable phase measurements [10], [6]....
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...Geometrical decorrelation [10], [25] limits the number of image pairs suitable for interferometric applications and prevents one from fully exploiting the data set available....
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...Temporal decorrelation [10] makes InSAR measurements unfeasible over vegetated areas and where the electromagnetic profiles and/or the positions of the scatterers change with time within the resolution cell....
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TL;DR: In this article, the authors used Synthetic Aperture Radar (SAR) interferometry to capture the movements produced by the 1992 earthquake in Landers, California, by combining topographic information with SAR images obtained by the ERS-1 satellite before and after the earthquake.
Abstract: GEODETIC data, obtained by ground- or space-based techniques, can be used to infer the distribution of slip on a fault that has ruptured in an earthquake. Although most geodetic techniques require a surveyed network to be in place before the earthquake1–3, satellite images, when collected at regular intervals, can capture co-seismic displacements without advance knowledge of the earthquake's location. Synthetic aperture radar (SAR) interferometry, first introduced4 in 1974 for topographic mapping5–8 can also be used to detect changes in the ground surface, by removing the signal from the topography9,10. Here we use SAR interferometry to capture the movements produced by the 1992 earthquake in Landers, California11. We construct an interferogram by combining topographic information with SAR images obtained by the ERS-1 satellite before and after the earthquake. The observed changes in range from the ground surface to the satellite agree well with the slip measured in the field, with the displacements measured by surveying, and with the results of an elastic dislocation model. As a geodetic tool, the SAR interferogram provides a denser spatial sampling (100 m per pixel) than surveying methods1–3 and a better precision (∼3 cm) than previous space imaging techniques12,13.
1,970 citations
"Permanent scatterers in SAR interfe..." refers methods in this paper
...REPEAT-pass satellite SAR interferometry (InSAR) is potentially a unique tool for low cost precise digital elevation models (DEM) generation and large-coverage surface deformation monitoring [9], [12], [16], [17]....
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TL;DR: In this article, a new approach to the estimation of the atmospheric phase contributions, and the local displacement field is proposed based on simple statistical assumptions, is presented in order to cope with nonlinear motion of the targets.
Abstract: Discrete and temporarily stable natural reflectors or permanent scatterers (PS) can be identified from long temporal series of interferometric SAR images even with baselines larger than the so-called critical baseline. This subset of image pixels can be exploited successfully for high accuracy differential measurements. The authors discuss the use of PS in urban areas, like Pomona, CA, showing subsidence and absidence effects. A new approach to the estimation of the atmospheric phase contributions, and the local displacement field is proposed based on simple statistical assumptions. New solutions are presented in order to cope with nonlinear motion of the targets.
1,901 citations