Oscar Mora

Linear and nonlinear terrain deformation maps from a reduced set of interferometric SAR images

In this paper, an advanced technique for the generation of deformation maps using synthetic aperture radar (SAR) data is presented. The algorithm estimates the linear and nonlinear components of the displacement, the error of the digital elevation model (DEM) used to cancel the topographic terms, and the atmospheric artifacts from a reduced set of low spatial resolution interferograms. The pixel candidates are selected from those presenting a good coherence level in the whole set of interferograms and the resulting nonuniform mesh tessellated with the Delauney triangulation to establish connections among them. The linear component of movement and DEM error are estimated adjusting a linear model to the data only on the connections. Later on, this information, once unwrapped to retrieve the absolute values, is used to calculate the nonlinear component of movement and atmospheric artifacts with alternate filtering techniques in both the temporal and spatial domains. The method presents high flexibility with respect to the required number of images and the baselines length. However, better results are obtained with large datasets of short baseline interferograms. The technique has been tested with European Remote Sensing SAR data from an area of Catalonia (Spain) and validated with on-field precise leveling measurements.

A small-baseline approach for investigating deformations on full-resolution differential SAR interferograms

This paper presents a differential synthetic aperture radar (SAR) interferometry (DIFSAR) approach for investigating deformation phenomena on full-resolution DIFSAR interferograms. In particular, our algorithm extends the capability of the small-baseline subset (SBAS) technique that relies on small-baseline DIFSAR interferograms only and is mainly focused on investigating large-scale deformations with spatial resolutions of about 100/spl times/100 m. The proposed technique is implemented by using two different sets of data generated at low (multilook data) and full (single-look data) spatial resolution, respectively. The former is used to identify and estimate, via the conventional SBAS technique, large spatial scale deformation patterns, topographic errors in the available digital elevation model, and possible atmospheric phase artifacts; the latter allows us to detect, on the full-resolution residual phase components, structures highly coherent over time (buildings, rocks, lava, structures, etc.), as well as their height and displacements. In particular, the estimation of the temporal evolution of these local deformations is easily implemented by applying the singular value decomposition technique. The proposed algorithm has been tested with data acquired by the European Remote Sensing satellites relative to the Campania area (Italy) and validated by using geodetic measurements.

Landslide Activity Maps Generation by Means of Persistent Scatterer Interferometry

In this paper a methodology is proposed to elaborate landslide activity maps through the use of PS (Persistent Scatterer) data. This is illustrated through the case study of Tramuntana Range in the island of Majorca (Spain), where ALOS (Advanced Land Observing Satellite) images have been processed through a Persistent Scatterer Interferometry (PSI) technique during the period of 2007–2010. The landslide activity map provides, for every monitored landslide, an assessment of the PS visibility according to the relief, land use, and satellite acquisition parameters. Landslide displacement measurements are projected along the steepest slope, in order to compare landslide velocities with different slope orientations. Additionally, a ground motion activity map is also generated, based on active PS clusters not included within any known landslide phenomenon, but even moving, potentially referred to unmapped landslides or triggered by other kinds of geomorphological processes. In the Tramuntana range, 42 landslides were identified as active, four as being potential to produce moderate damage, intersecting the road Ma-10, which represents the most important road of the island and, thus, the main element at risk. In order to attest the reliability of measured displacements to represent landslide dynamics, a confidence degree evaluation is proposed. In this test site, seven landslides exhibit a high confidence degree, medium for 93 of them, and low for 51. A low confidence degree was also attributed to 615 detected active clusters with a potential to cause moderate damage, as their mechanism of the triggering cause is unknown. From this total amount, 18 of them intersect the Ma-10, representing further potentially hazardous areas. The outcomes of this work reveal the usefulness of landslide activity maps for environmental planning activities, being exportable to other radar data and different geomorphological settings.

A new algorithm for monitoring localized deformation phenomena based on small baseline differential SAR interferograms

This paper presents a new solution for detecting and following the temporal evolution of small scale deformation phenomena; in particular our approach extends the capability of the SBAS technique, presented in P. Berardino et al. (2001), which is mainly focused on investigating large scale deformations with spatial resolutions of about 100 m/spl times/100 m. The proposed technique relies on small baseline differential SAR (DIFSAR) interferograms only, but it is implemented by using two different sets of data generated at low (multi-look data) and high spatial resolution (single-look data), respectively. The former are used to identify and estimate, via the SBAS technique or O. Mora et al. (2001, 2002), possible atmospheric phase artifacts and large scale deformation patterns; the latter to detect, on the high resolution residual phase components, structures highly coherent in time (buildings, rocks, lava structures, etc.), identified jointly to their heights and displacements. In particular the estimation of the temporal evolution of these local deformations is easily implemented by applying the SVD technique. The presented algorithm has been tested with data acquired by the European Remote Sensing (ERS) satellites relative to the Campania area (Italy).

Generation of deformation maps at low resolution using differential interferometric SAR data

In this paper, an advanced technique for the generation of deformation maps using SAR data is presented. The input data is a set of low resolution Differential Interferograms (multi-looked data) and their associated coherence images. An important advantage of this algorithm is that it can work with a reduced number of SAR images with a diversity of spatial baselines. The algorithm takes advantage of those pixels presenting a good coherence level in the whole set of interferograms, avoiding the rest affected by temporal decorrelation. All pixels accomplishing the selection criteria are related using a Delaunay triangulation. The subsidence velocity map over the scene is obtained adjusting an interferometric phase model, which also considers the error on the DEM used to remove the topography from the interferogram set, to the pixel phase increments. If the density of quality pixels is high enough over the scene, an interpolation of the areas with no information can be performed to obtain a complete deformation map of the zone. Otherwise, the information can be presented only on those zones with enough pixel density. This algorithm has been tested with ERS data from an area of Catalonia (Spain) and validated with precise levelling measurements.

Long-term subsidence monitoring of urban areas using differential interferometric SAR techniques

Subsidence monitoring of areas affected by low velocity displacements is an extremely useful application of SAR (synthetic aperture radar) techniques. However, the required long time-baselines reduce the quality of the information stored in differential interferograms, adding difficulties to their processing. Typical characteristics of these interferograms are the presence of coherent areas that correspond to urban zones and totally incoherent areas of vegetation. A partial reconstruction of the subsidence map can be achieved by means of DInSAR (differential interferometric SAR) techniques based on the processing of coherent patches. On the other hand, PS (permanent scatterers) techniques can deal with incoherent areas, generating subsidence information of the whole image. A comparison of both techniques using ERS data is presented in this paper.

A multi-sensor approach for monitoring a road bridge in the Valencia harbor (SE Spain) by SAR Interferometry (InSAR)

This project was developed in the framework of the DORIS project (ground deformation risk scenarios: an advanced assessment service) funded by the EC-GMES-FP7 initiative (grant agreement 423 no. 242212) and by the Spanish Ministry of Economy and Competitiveness (MINECO) and EU FEDER, under project TIN2014-55413- C2-2-P. ALOS PALSAR images were provided by the project JAXA- 1209. The authors thank the University of Florence for founding Matteo Del Soldato for the PhD abroad period of research to the Department of Civil Engineering of the University of Alicante and the Autoridad Portuaria de Valencia for its kindly support.

Phase statistics and quality evaluation of deformation maps with multiple-image differential interferometry

This paper presents a closed formulation to evaluate the quality of terrain deformation maps obtained with multi-image differential interferometry. The analytical formulation, based on the application of the asymptotic covariance matrix, that propagates the interferogram coherences to the linear deformation and DEM error accuracies when using a stack of interferograms, is developed and validated with real data from the ERS satellites.

Generation of precise wide-area geocoded elevation models with ERS SAR data

The authors present an improved technique for the generation of digital elevation models (DEM), capable of dealing with full scene images (100/spl times/100 km) coming from an interferogram obtained with ERS satellite data. Starting from an interferometric processor aimed to the geocoding of smaller areas, now the authors expound the new improvements based on the use of ground control points (GCP) in order to calibrate some imprecisions which appear in the case of very wide swaths. A generated DEM of the test zone of Tarragona (Spain) and its error assessment are presented.

The European DORIS downstream service as a multi-scale system for landslides and subsidence risk management

We focused on the joint exploitation of satellite and ground-based technologies in order to understand the kinematic behavior of landslides and subsidence phenomena relevant to different test sites in Europe. In this context, we efficiently exploited C-band and X-band satellite and ground-based SAR data for the investigation of the temporal and spatial pattern of ground deformations caused by natural and human-induced hazards. The present work has been conducted within the FP7-EU DORIS project.