Investigating landslides with space-borne Synthetic Aperture Radar (SAR) interferometry

Persistent Scatterer Interferometry (PSI) is a powerful remote sensing technique able to measure and monitor displacements of the Earth’s surface over time. Specifically, PSI is a radar-based technique that belongs to the group of differential interferometric Synthetic Aperture Radar (SAR). This paper provides a review of such PSI technique. It firstly recalls the basic principles of SAR interferometry, differential SAR interferometry and PSI. Then, a review of the main PSI algorithms proposed in the literature is provided, describing the main approaches and the most important works devoted to single aspects of PSI. A central part of this paper is devoted to the discussion of different characteristics and technical aspects of PSI, e.g. SAR data availability, maximum deformation rates, deformation time series, thermal expansion component of PSI observations, etc. The paper then goes through the most important PSI validation activities, which have provided valuable inputs for the PSI development and its acceptability at scientific, technical and commercial level. This is followed by a description of the main PSI applications developed in the last fifteen years. The paper concludes with a discussion of the main open PSI problems and the associated future research lines.

https://zenodo.org/record/45568/files/Persistent_Scatterer_Interferometry.pdf

Persistent Scatterer Interferometry: A review

Spaceborne differential synthetic aperture radar interferometry (DInSAR) has already proven its potential for mapping ground deformation phenomena, e.g. volcano dynamics. However, atmospheric disturbances as well as phase decorrelation have prevented hitherto this technique from achieving full operational capability. These drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to pointwise stable reflectors (Permanent Scatterers, PS) and exploiting long temporal series of interferometric data. Results obtained by processing 55 images acquired by the European Space Agency (ESA) ERS SAR sensors over Southern California show that the PS approach pushes measurement accuracy very close to its theoretical limit (about 1 mm), allowing the description of millimetric deformation phenomena occurring in a complex fault system. A comparison with corresponding displacement time series relative to permanent GPS stations of the Southern California Integrated GPS network (SCIGN) is carried out. Moreover, the pixel-by-pixel character of the PS analysis allows the exploitation of individual phase stable radar targets in low-coherence areas. This makes spaceborne interferometric measurements possible in vegetated areas, as long as a sufficient spatial density of individual isolated man-made structures or exposed rocks is available. The evolution of the Ancona landslide (central Italy) was analysed by processing 61 ERS images acquired in the time span between June 1992 and December 2000. The results have been compared with deformation values detected during optical levelling campaigns ordered by the Municipality of Ancona. The characteristics of PS, GPS and optical levelling surveying are to some extent complementary: a synergistic use of the three techniques could strongly enhance quality and reliability of ground deformation monitoring. D 2002 Elsevier Science B.V. All rights reserved.

Monitoring Landslides and Tectonic Motions with the Permanent Scatterers Technique

Investigating landslides and unstable slopes with satellite Multi Temporal Interferometry: Current issues and future perspectives

This paper presents the results of a blind experiment that is performed using two pairs of dihedral reflectors. The aim of the experiment was to demonstrate that interferometric synthetic aperture radar (InSAR) measurements can indeed allow a displacement time series estimation with submillimeter accuracy (both in horizontal and vertical directions), provided that the data are properly processed and the impact of in situ as well as atmospheric effects is minimized. One pair of dihedral reflectors was moved a few millimeters between SAR acquisitions, in the vertical and east-west (EW) directions, and the ground truth was compared with the InSAR data. The experiment was designed to allow a multiplatform and multigeometry analysis, i.e., each reflector was carefully pointed in order to be visible in both Envisat and Radarsat acquisitions. Moreover, two pairs of reflectors were used to allow the combination of data gathered along ascending and descending orbits. The standard deviation of the error is 0.75 mm in the vertical direction and 0.58 mm in the horizontal (EW) direction. GPS data were also collected during this experiment in order to cross-check the SAR results

/pdf/submillimeter-accuracy-of-insar-time-series-experimental-11qq7gtfbs.pdf

Submillimeter Accuracy of InSAR Time Series: Experimental Validation

The Permanent Scatterers (PS) technique is an advanced tool for processing series of interferometric SAR data aiming at millimetric precision ground deformation mapping. The approach is based on a joint time-space-acquisition geometry analysis that is carried out at individual point-wise radar targets. The aim of this paper is twofold: (1) describe the main issues related to the precision of PS products; (2) show preliminary PS results obtained using, instead of ESA-ERS scenes, data acquired by other spaceborne SAR platforms characterized different acquisition parameters (namely RADARSAT and JERS).

Permanent Scatterers: precision assessment and multi-platform analysis

The PS technique is an advanced tool for the joint exploitation of series of interferometric SAR data for measuring millimetric ground deformation effects on privileged radar targets. In this paper we briefly discuss some preliminary results obtained in the first attempt to apply the permanent scatterers (PS) technique on a RADARSAT data set.

Multi-platform permanent scatterers analysis: first results

As well known, the Permanent Scatterers (PS) Technique [1] is an advanced tool for processing series of interferometric SAR data aiming at ground deformation mapping with millimetric precision. Even though the potential of this approach has been already proved in several applications, ranging from urban subsidence monitoring to landslide detection in Alpine region, it is in general very difficult to obtain a comprehensive validation of the estimated measurements. The problem, in many cases, stems from the lack of ground truth or to the availability of measurements that are difficult to compare with those obtained from InSAR, due to the different temporal coverage and/or acquisition geometry. In order to perform a comprehensive validation of the InSAR approach and to assess the limits of its applicability, a blind experiment has been carried out by Politecnico di Milano and TRE in cooperation with the Centro Elettrotecnico Sperimentale Italiano (CESI), in the framework of a research activity financed by the public fund for the Italian Electric System. Two couples of dihedral reflectors have been deployed and pointed so that the reflectors were visible along ascending orbits of both Envisat and Radarsat platforms. The aim of the experiment was to move one couple of dihedral reflectors of a few millimetres from one acquisition to another, along both vertical and East-West direction, and to compare these displacements with those estimated by means of interferometric measurements applied to ascending and descending data. In this paper, the results of the experiment carried out using a series of 25 Radarsat and 8 Envisat acquisitions (considering both ascending and descending data) are reported for the first time. Data allow the comparison of the estimated time series with the imposed motion: a standard deviation of just 1 mm has been measured for both horizontal and vertical components.

PSInSAR Validation by means of a blind experiment using dihedral reflectors

https://earth.esa.int/workshops/fringe2005/proceedings/papers/253_novali.pdf

G. Savio

Papers

Submillimeter Accuracy of InSAR Time Series: Experimental Validation

Permanent Scatterers: precision assessment and multi-platform analysis

Multi-platform permanent scatterers analysis: first results

PSInSAR Validation by means of a blind experiment using dihedral reflectors

PSInSAR Validation by Means of a Blind Experiment Using Dihedral Reflectors