S. Usai

A least squares database approach for SAR interferometric data

Presents a least squares (LS) approach for the retrieval of a temporal deformation sequence from a set of interferometric synthetic aperture radar images. The method uses a database of interferograms spanning different longand short-term intervals, and by solving all the deformations as a unique LS problem provides a chronologically ordered sequence, i.e. a picture of the development of the deformation pattern in time. The approach is illustrated in detail and discussed with respect to both the results of its application on a case study and to possible alternative methods.

SAR interferometry on a very long time scale: a study of the interferometric characteristics of man-made features

Anthropogenic features show up as highly coherent objects even in heavily decorrelated interferograms. In order to assess whether the information from such features is still usable, the stability of their phase and coherence is analyzed through a series of interferograms. The results indicate that these features can remain interferometrically stable over several years.

An analysis of the interferometric characteristics of anthropogenic features

A study of the interferometric characteristics of manmade features is presented. Tests for the assessment of their phase stability are applied for two case studies. The results indicate that small features show spatially homogeneous phase information in a single interferogram and that this information remains stable also in time even at the level of single pixels.

A new approach for analyzing the temporal evolution of Earth surface deformations based on the combination of DIFSAR interferograms

We present a new approach for the evaluation of the Earth surface deformation evolution based on the combination of several differential interferograms spanning a time interval of interest. In particular we present a method that extends the least squares combination technique presented by S. Usai et al. (2000) by applying the singular value decomposition (SVD) method. Experiments carried out on ERS data validate the proposed approach.

The use of man-made features for long time scale INSAR

From a series of interferograms spanning 3 and 1/2 years, a sample of features has been extracted which appear to have constantly high coherence for the whole time interval. These features, mainly of anthropogenic nature, have then been studied in order to assess whether they can be used for long time monitoring of slow deformation processes in almost completely decorrelated areas. For this purpose, both the coherence and the phase stability of the features have been checked along the time series.

On the feasibility of long time scale INSAR

A study on the applicability of the INSAR technique on long time scales is presented. The authors generated a database of 69 ERS-1/ERS-2 interferograms of the Groningen area, in the north of The Netherlands, spanning the years from 1992 to 1996. From this database they tried to extract information on the phase stability of man-made features. For this purpose the differential technique has been applied on the interferometric phase values of high coherence pixels along a road. These resulted to be stable in 90% of the cases at the level of 0.6 cm, even on time scales of more years. Also many isolated man-made features revealed the same phase stability in time.

A least-squares approach for long-term monitoring of deformations with differential SAR interferometry

A least-squares (LS) approach is presented for the retrieval of a temporal deformation sequence from a database of interferometric SAR images. The method uses a database of interferograms, and by solving all the deformations as a unique least squares problem provides a chronologically ordered sequence, describing the development of the deformation pattern in time. The LS approach is illustrated in detail and discussed with respect to the results of its application on a test site.

Modelling terrain deformations at the Phlegrean Fields with INSAR

An approach for the retrieval of long-term deformations from a set of differential interferograms is presented. The method consists in solving simultaneously in a least squares sense all the interferograms to determine the terrain deformations as a chronological sequence. With this approach, the temporal evolution of the subsidence in the neapolitan area of the Phlegrean Fields has been determined for the period 1993-1999.

On the interferometric characteristics of anthropogenic features

A new approach for the measurement of deformations with SAR interferometry in scarcely decorrelated, long term interferograms is presented. The approach makes use of the interferometric phase information from highly coherent features, mostly of anthropogenic nature. The method has been applied to measure the deformations in a subsiding area in The Netherlands and the results turned out to be in good agreement with those from a pre-existing subsidence model.

MINERVA: an INSAR monitoring system for volcanic hazard

MINERVA (Monitoring by Interferometric SAR of Environmental Risk in Volcanic Areas) is a small scale service demonstration project financed by ESA in the Data User Programme framework. The objective of the project is the design, development and assessment of a demonstrative information service based on the interferometric processing of images from the ASAR instruments on board ERS1/2 and ENVISAT-I. The system is based on a new approach for the processing of INSAR data, which allows to optimize the quality of interferograms spanning from 35 days up to several years, and to merge them to generate a single solution describing the temporal evolution of the ground deformations in the examined risk area. The system allows to update this solution each time a new SAR image is available, and constitutes therefore an innovative tool for monitoring of the ground displacements in risk areas.