Giovanni Nico

Temporal analysis of a landslide by means of a ground-based SAR Interferometer

A ground-based synthetic aperture radar (GB-SAR) interferometer is used to retrieve the velocity field of a landslide. High-resolution images are obtained by means of a time domain SAR processor. An in-depth analysis of the sequence of SAR interferograms enables the recognition of a slowly deforming upper scarp in the scene, and a debris flow that feeds the accumulation zone of the landslide, where a fast change in terrain morphology is observed. The estimated deformation map is in agreement with the available measurements obtained by means of Global Positioning System receivers. Results show that GB-SAR interferometry is a cost-effective solution for the monitoring of landslides. The proposed method is shown to be a valid complement to space- and airborne SAR and to the traditional geodetic instruments.

Merging GPS and Atmospherically Corrected InSAR Data to Map 3-D Terrain Displacement Velocity

A method to derive accurate spatially dense maps of 3-D terrain displacement velocity is presented. It is based on the merging of terrain displacement velocities estimated by time series of interferometric synthetic aperture radar (InSAR) data acquired along ascending and descending orbits and repeated GPS measurements. The method uses selected persistent scatterers (PSs) and GPS measurements of the horizontal velocity. An important step of the proposed method is the mitigation of the impact of atmospheric phase delay in InSAR data. It is shown that accurate vertical velocities at PS locations can be retrieved if smooth horizontal velocity variations can be assumed. Furthermore, the mitigation of atmospheric effects reduces the spatial dispersion of vertical velocity estimates resulting in a more spatially regular 3-D velocity map. The proposed methodology is applied to the case study of Azores islands characterized by important tectonic phenomena.

Ground-based SAR interferometry for terrain mapping: theory and sensitivity analysis

This short communication studies the problem of terrain mapping by means of the ground-based synthetic aperture radar (GB-SAR) interferometry technique. A phase-to-height relationship tailored for the GB-SAR interferometric configuration is introduced and verified by a simulated analysis. A sensitivity study is carried out aiming to optimize the use of a GB-SAR system for the terrain mapping and to derive the precision of this technique.

NEW REGULARIZATION SCHEME FOR PHASE UNWRAPPING

A new, to our knowledge, algorithm for the phase unwrapping (PU) problem that is based on stochastic relaxation is proposed and analyzed. Unlike regularization schemes previously proposed to handle this problem, our approach dispells the following two assumptions about the solution: a Gaussian model for noise and the magnitude of the true phase-field gradients being less than pi everywhere. We formulate PU as a constrained optimization problem for the field of integer multiples of 2pi, which must be added to the wrapped phase gradient to recover the true phase gradient. By solving the optimization problem using simulated annealing with constraints, one can obtain a consistent solution under difficult conditions resulting from noise and undersampling. Results from synthetic test images are reported.

Experimental Study on the Atmospheric Delay Based on GPS, SAR Interferometry, and Numerical Weather Model Data

In this paper, we present the results of an experiment aiming to compare measurements of atmospheric delay by synthetic aperture radar (SAR) interferometry and GPS techniques to estimates by numerical weather prediction. Maps of the differential atmospheric delay are generated by processing a set of interferometric SAR images acquired by the ENVISAT-ASAR mission over the Lisbon region from April to November 2009. GPS measurements of the wet zenith delay are carried out over the same area, covering the time interval between the first and the last SAR acquisition. The Weather Research and Forecasting (WRF) model is used to model the atmospheric delay over the study area at about the same time of SAR acquisitions. The analysis of results gives hints to devise mitigation approaches of atmospheric artifacts in SAR interferometry applications.

On the Use of the WRF Model to Mitigate Tropospheric Phase Delay Effects in SAR Interferograms

A method that is used to generate synthetic interferograms of the atmospheric phase delay temporal changes is presented. The Weather Research and Forecasting Model is used to forecast the spatial distribution of the main atmospheric parameters at the acquisition times of synthetic aperture radar (SAR) images. The method is applied to mitigate atmospheric artifacts in SAR interferograms. The Lisbon Region and the Pico and Faial Islands in the Azores archipelago are chosen as case studies. They are characterized by a different temporal behavior of atmospheric phase delay properties. Results are assessed by means of a statistical analysis.

Assessing scientific collaboration through coauthorship and content sharing

Over the past decade there have been many investigations aimed at defining the role of scientists and research groups in their coauthorship networks. Starting from the assumptions of network analysis, in this work we propose an analytical definition of a collaboration potential between authors of scientific papers based on both coauthorships and content sharing. The collaboration potential can also be considered a useful tool to investigate the relationships between a single scientist and research groups, thus allowing for the identification of characteristic “types” of scientists (integrated, independent, etc.). We computed the collaboration potential for a set of authors belonging to research groups of an institute specialized in the field of Medical Genetics. The methods presented in the paper are rather general as they can be applied to compute a collaboration potential for a network of cooperating actors in every situation in which one can qualify the content of some activities and which of them are in common among the actors of the network.

Bridging InSAR and GPS Tomography: A New Differential Geometrical Constraint

The integration of interferometric synthetic aperture radar (InSAR) and GPS tomography techniques for the estimation of the 3-D distribution of atmosphere refractivity is discussed. A methodology to use the maps of the temporal changes of precipitable water vapor (PWV) provided by InSAR as a further constraint in the GPS tomography is described. The aim of the methodology is to increase the accuracy of the GPS tomography reconstruction of the atmospheres refractivity. The results, which are obtained with SAR and GPS data acquired over the Lisbon area, Portugal, are presented and assessed. It has been found that the reconstruction of the atmospheric refractivity is closer to the real atmospheric state with a mitigation of the smoothing effects due to the usual geometrical constraints of the GPS tomography.

Ground-based SAR interferometry as a tool for landslide monitoring during emergencies

This work concerns the application of ground-based synthetic aperture radar (GB-SAR) interferometry as a tool for the landslide monitoring during emergencies. An example of application of this technique to the Cortenova landslide, Italian Alps, is described. The deformation maps provided by GB-SAR interferometry allows for the study of the landslide temporal evolution and the volume estimation of the material involved in the mass movement. This information is important for the assessment of future risk scenarios needed to draw up the emergency plans for civil protection purposes.

A ground-based interferometer for the safety monitoring of landslides and structural deformations

This paper concerns the use of Ground-Based Synthetic Aperture Radar (GB-SAR) interferometer for the measurement of terrain movements and structural deformations in man-made structures. This instrument can measure displacements with a precision up to a fraction of millimetre. The spatial extension of the monitored area can be of a few squared kilometres. With respect to other traditional geotechnical instruments, the presented GB-SAR interferometer can remotely monitor the target scene, providing deformation maps and not only point-like measurements.