Alessandro Ferretti - Academia.edu (original) (raw)

Papers by Alessandro Ferretti

Underground. The Way to the Future, 2013

ABSTRACT Interferometry of Synthetic Aperture Radar (SAR) imagery from the ERS-1and2 satellites h... more ABSTRACT Interferometry of Synthetic Aperture Radar (SAR) imagery from the ERS-1and2 satellites has been used to produce a digital terrain model (DTM) of the 48 km-diameter Velingara structure in Casamance, Senegal, which strongly resembles an impact structure.

Eos, Transactions American Geophysical Union, 2004

made valuable contributions to CALIPSO, and their efforts are also acknowledged.A. Clarke also co... more made valuable contributions to CALIPSO, and their efforts are also acknowledged.A. Clarke also contributed to CALIPSO through initial model development.

3rd IAG/12th FIG …, 2006

Synthetic Aperture Radar Interferometry (InSAR) from Earth-orbiting spacecraft has revolutionized... more Synthetic Aperture Radar Interferometry (InSAR) from Earth-orbiting spacecraft has revolutionized the field of crustal deformation research since its first geophysical application, about a decade ago. During the last 10 years, InSAR has been used to study a wide range of surface displacements related to active faults, volcanoes, landslides, aquifers, oil fields and glaciers, to name just a few, at a spatial resolution of less than 100 m and cm-level precision. The temporal resolution is limited by the monthly repeat time of satellite flyovers. Due to the viewing geometry of the radar satellite, InSAR is particularly sensitive to vertical deformation, but can not detect displacements parallel to the orbit track. Severe limitations to the InSAR method remain, especially decorrelation of surface scatterers due to vegetation or other surface change processes, incoherence caused by large satellite orbit separations between the two image acquisitions used to make an interferogram, and noise from signal delays in the Earth's atmosphere.

Spaceborne differential radar interferometry has already proven its potential for mapping ground ... more Spaceborne differential radar interferometry has already proven its potential for mapping ground deformation phenomena in application to, among others, volcano dynamics, co-seismic and post-seismic displacements of faults and slope instability. 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 natural or artificial stable reflectors (Permanent Scatterers, PS) and exploiting temporal series of interferometric data. Results obtained by processing 55 Synthetic Aperture Radar acquisitions of ERS satellites (European Space Agency) over Southern California, show that this approach allows one to push measurement accuracy very close to its theoretical limit of one millimetre. Though a full 3D displacement field cannot be recovered, the spatial density of measurements (up to 300 PS/km2), their ...

IEEE Transactions on Geoscience and Remote Sensing, 2000

Discrete and temporarily stable natural reflectors or permanent scatterers (PS) can be identified... more 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. We 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.

Engineering Geology, 2003

Spaceborne differential synthetic aperture radar interferometry (DInSAR) has already proven its p... more 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.

SPE Annual Technical Conference and Exhibition, 2010

Surface deformation monitoring can provide valuable information in assessing the environmental im... more Surface deformation monitoring can provide valuable information in assessing the environmental impact of activities, evaluating volume/pressure changes in a reservoir, as well as estimating other geophysical parameters. Eni and stogit have been studying the use of Interferometric Synthetic Aperture Radar (InSAR) data for surface deformation monitoring since 2001. Based on almost 10 years of R&D and operational projects, this paper aims to summarise the strengths and weaknesses of this space geodetic tool, as well as providing an outlook on future developments in the up and down-stream activities. During the last decade, satellite InSAR data have been gaining increasing attention for their unique technical features and cost- effectiveness. In particular, second-generation InSAR techniques (e.g. PSInSAR™) are capable of providing thousands of displacement measurements per sqkm at millimeter precision. Since 2001, eni has financed projects based on InSAR data, first for environmental a...

2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2015

This study presents the spatial and temporal grounddeformation pattern of the Nisyros-Yali volcan... more This study presents the spatial and temporal grounddeformation pattern of the Nisyros-Yali volcanic field after the period of the seismic crisis (1996-1998) based on the local GPS network remeasurement and the analysis of Interferometric data (2003-2010) applying the SqueeSAR TM technique. The GPS results indicated intense subsidence in the northern and central parts of Nisyros that caused the western and eastern flanks of the island to "collapse" towards its center. The observed LOS velocity field of the SqueeSAR TM analysis revealed a nearly linear type of ground deformation, exhibiting values ranging between-3 to +3mm/yr with small standard deviations. The interferometric results have also shown subsidence along the northern and central parts of the island, and an inherent eastward horizontal component at its southeastern part. The overall pattern of the observed subsidence in the area after 2000 is consistent with decrease of pressure in the associated magma chambers and hydrothermal system.

International Conference on Landslide Risk Management, 18th Annual Vancouver Geotechnical Society Symposium, 31 maggio-3 giugno 2005, Canada, May 1, 2005

Remote Sensing of Environment, 2012

We describe the state of the art of scientific research on the earthquake cycle based on the anal... more We describe the state of the art of scientific research on the earthquake cycle based on the analysis of Synthetic Aperture Radar (SAR) data acquired from satellite platforms. We examine the achievements and the main limitations of present SAR systems for the measurement and analysis of crustal deformation, and envision the foreseeable advances that the Sentinel-1 data will generate in the fields of geophysics and tectonics. We also review the technological and scientific issues which have limited so far the operational use of satellite data in seismic hazard assessment and crisis management, and show the improvements expected from Sentinel-1 data.

2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, 2021

Interferometric processing of a time series of acquisitions from synthetic aperture radar (SAR) s... more Interferometric processing of a time series of acquisitions from synthetic aperture radar (SAR) satellites makes it possible to detect and measure ground motion phenomena, typically caused by landslides, subsidence, earthquakes or volcanic activity, with millimeter-scale precision. This enables, for example, monitoring of the stability of slopes, mining areas, buildings and infrastructures. This work presents the European Ground Motion Service (EGMS), funded by the European Commission as an essential element of the Copernicus Land Monitoring Service (CLMS). The EGMS constitutes the first application of the interferometric SAR (InSAR) technology to high-resolution monitoring of ground deformations over an entire continent, based on fullresolution processing of all Sentinel-1 (S1) satellite acquisitions over most of Europe (Copernicus Participating States). Upscaling from existing national precursor services to pan-European scale is challenging. The EGMS will employ the most advanced persistent scatterer (PS) and distributed scatterer (DS) InSAR processing techniques in combination with a high-quality Global Navigation Satellite System (GNSS) model to calibrate the ground motion products. To foster as wide usage as possible, the EGMS will also provide tools for visualization, exploration, analysis and download of the ground deformation products, as well as elements to promote best practice applications and user uptake.

First Break, 2013

3* show, with a case study from the InSalah project, Algeria, the benefits of a new application o... more 3* show, with a case study from the InSalah project, Algeria, the benefits of a new application of surface deformation monitoring using multi-interferogram permanent scatterer techniques, an advance form of radar interferometry.

Second EAGE CO2 Geological Storage Workshop 2010, 2010

Scientific reports, Jan 8, 2018

We present the continuous monitoring of ground deformation at regional scale using ESA (European ... more We present the continuous monitoring of ground deformation at regional scale using ESA (European Space Agency) Sentinel-1constellation of satellites. We discuss this operational monitoring service through the case study of the Tuscany Region (Central Italy), selected due to its peculiar geological setting prone to ground instability phenomena. We set up a systematic processing chain of Sentinel-1 acquisitions to create continuously updated ground deformation data to mark the transition from static satellite analysis, based on the analysis of archive images, to dynamic monitoring of ground displacement. Displacement time series, systematically updated with the most recent available Sentinel-1 acquisition, are analysed to identify anomalous points (i.e., points where a change in the dynamic of motion is occurring). The presence of a cluster of persistent anomalies affecting elements at risk determines a significant level of risk, with the necessity of further analysis. Here, we show t...

Proceedings of the International Association of Hydrological Sciences, 2015

Satellite interferometric synthetic aperture radar (InSAR) data have proven effective and valuabl... more Satellite interferometric synthetic aperture radar (InSAR) data have proven effective and valuable in the analysis of urban subsidence phenomena based on multi-temporal radar images. Results obtained by processing data acquired by different radar sensors, have shown the potential of InSAR and highlighted the key points for an operational use of this technology, namely: (1) regular acquisition over large areas of interferometric data stacks; (2) use of advanced processing algorithms, capable of estimating and removing atmospheric disturbances; (3) access to significant processing power for a regular update of the information over large areas. In this paper, we show how the operational potential of InSAR has been realized thanks to the recent advances in InSAR processing algorithms, the advent of cloud computing and the launch of new satellite platforms, specifically designed for InSAR analyses (e.g. Sentinel-1a operated by the ESA and ALOS2 operated by JAXA). The processing of thousands of SAR scenes to cover an entire nation has been performed successfully in Italy in a project financed by the Italian Ministry of the Environment. The challenge for the future is to pass from the historical analysis of SAR scenes already acquired in digital archives to a near real-time monitoring program where up to date deformation data are routinely provided to final users and decision makers.

ABSTRACT The geological sequestration of CO2 is rapidly becoming recognized as the quickest metho... more ABSTRACT The geological sequestration of CO2 is rapidly becoming recognized as the quickest method to reduce GHG emissions. While research is ongoing regarding the most efficient ways to capture CO2 from gas streams the decades old experience of the oil industry with EOR means that tested injection technology is already available. However, public opinion demands that rigorous monitoring methods be used to ascertain that injected CO2 stay permanently stored. Utmost importance must be given, therefore, to the identification and use of tools capable of monitoring plume development. Given the depths involved and the often heterogeneous nature of the subsurface this is a challenging task that requires integration of numerous techniques. A Joint Venture between BP, Sonatrach and StatoilHydro has been injecting CO2 at the In Salah gas field in Algeria since 2004 at a rate of almost 1 million tons of CO2 per year [1]. To demonstrate best-practice application of CO2 storage monitoring, integrity and verification technologies, the In Salah Gas CO2 Storage Assurance Joint Industry Project was also set up in 2004. Participants include academia, the US DoE and the EU. The use of PSInSAR™ as a viable monitoring tool was demonstrated within this framework. PSInSAR™ is a radar satellite technique that detects and measures ground movement with a high degree of precision. Compared to differential interferometry (DInSAR), which uses only two radar images, PSInSAR™ significantly increases the accuracy of movement measurement by processing an entire stack of radar images. This allows atmospheric effects to be removed from the results and in ideal conditions average ground deformation rates can be measured with an error of less than 1 mm/yr [2]. Several other characteristics of the technique make it a valuable tool for CO2 injection monitoring: 1) It can produce a high spatial density of measurement points (PS) on the ground; 2) It can cover large areas, extending to thousands of square kilometers, without loss of precision; 3) It is a time lapse technique.

ABSTRACT Surface deformation monitoring provides unique data for observing and measuring the perf... more ABSTRACT Surface deformation monitoring provides unique data for observing and measuring the performance of producing hydrocarbon reservoirs, for Enhanced Oil Recovery (EOR) and for Carbon Dioxide Capture and Storage (CCS). To this aim, radar interferometry (InSAR) and, in particular, multi-interferogram Permanent Scatterer (PS) techniques are innovative, valuable and cost-effective tools. Depending on reservoir characteristics and depth, oil or gas production can induce surface subsidence or, in the cases of EOR and CCS, ground heave, potentially triggering fault reactivation and in some cases threatening well integrity. Mapping the surface effects of fault reactivation, due to either fluid extraction or injection, usually requires the availability of hundreds of measurement points per square km with millimeter-level precision, which is time consuming and expensive to obtain using traditional monitoring techniques, but can be readily obtained with InSAR data. Moreover, more advanced InSAR techniques developed in the last decade are capable of providing millimeter precision, comparable to optical leveling, and a high spatial density of displacement measurements, over long periods of time without need of installing equipment or otherwise accessing the study area. Until recently, a limitation to the application of InSAR was the relatively long revisiting time (24 or 35 days) of the previous generation of C-band satellites (ERS1-2, Envisat, Radarsat). However, a new generation of X-band radar satellites (TerraSAR-X and the COSMO-SkyMed constellation), which have been operational since 2008, are providing significant improvements. TerraSAR-X has a repeat cycle of 11 days while the two sensors of the COSMO-SkyMed constellation have an effective repeat cycle of just 8 days (the third sensor has already been successfully launched and is presently in the calibration phase). With the launch of the fourth satellite of the constellation, COSMO-SkyMed will have a revisiting time of just 4 days, allowing ``near real-time'' applications. Additional advantages of the new X-band satellites are: a higher sensitivity to target displacement and a higher spatial resolution. In this paper, we present examples of X-band applications to reservoir monitoring with the aim of highlighting the technical features of the new sensors, the importance of continuous data acquisition and standardized acquisition policies for all InSAR applications.

ABSTRACT SqueeSAR represents the most recent advancement of PSInSAR algorithm. By exploiting sign... more ABSTRACT SqueeSAR represents the most recent advancement of PSInSAR algorithm. By exploiting signal radar returns both from Permanent and Distributed Scatterers (PS and DS), it is able to detect millimetre displacements over long periods and large areas and to obtain a significant increase in the spatial density of ground measurement points. SqueeSAR analysis is complementary to conventional geological and geomorphological studies in landslide mapping over wide areas, traditionally based on aerial-photo interpretation and field surveys. However, whenever surface displacement rates are low (mm to cm per year), assessing landslide activity is difficult or even impossible without a long-term monitoring tool, as in the case of Deep-seated Gravitational Slope Deformations (DGSD), typically characterized by large areal extent and subtle surface displacement. The availability of surface displacement time series per each measurement point allows one to have both a synoptic overview, at regional scale, as well as an in depth characterization of the instability phenomena analyzed, a meaningful support to the design of traditional monitoring networks and the efficiency testing of remedial works. When data archives are available, SqueeSAR can also provide valuable information before the installation of any terrestrial measurement system. The Italian authorities increasing interest in the application of SqueeSAR as a standard monitoring tool to help hydrogeological risk assessment, resulted in a national project, Piano Straordinario di Telerilevamento (PST), founded by the Ministry of the Environment. The aim of the project was to create the first interferometric database on a national scale for mapping unstable areas. More than 12,000 ERS and ENVISAT radar scenes acquired over Italy were processed spanning the period 1992-2010, proving that, in less than ten years, radar interferometry has become a standard monitoring tool. Recently, many regional governments in Italy have applied SqueeSAR to map and monitor slope instabilities using ESA-ERS and RADARSAT images. One of the most successful was carried out in the Valle d'Aosta Region (NW Italy). The aim of the study was to support, verify and update the regional landslide inventory. The study covered a time span of about twenty years, from mid 1992 to late 2010. As many unstable areas of the region were reactivated in October 2000 by an intense meteorological event, the surface displacement data provided by traditional monitoring networks were compared at local scale with the displacement measured provided by SqueeSAR. This helped in better understanding the effects of the reactivation of the major landslides identified. Valle d'Aosta Region was the first authority to complete such a project at regional scale and make interpreted data officially available to professionals. Examples of integration of SqueeSAR data with other conventional geological and geomorphological studies at local and regional scale will be presented, with particular focus on DGSDs.

ABSTRACT InSAR is a remote sensing tool that has applications in both geothermal exploitation and... more ABSTRACT InSAR is a remote sensing tool that has applications in both geothermal exploitation and in the management of producing fields. The technique has developed rapidly in recent years and the most evolved algorithms, now capable of providing precise ground movement measurements with unprecedented spatial density over large areas, allow the monitoring of the effects of fluid injection and extraction on surface deformation and the detection of active faults. Multi-interferogram approaches have been used at several geothermal sites in different stages of development. SqueeSAR™, which represents the latest breakthrough in InSAR technology, provides a significant increase in the spatial density of measurement points by exploiting signal returns from both point-like and distributed scatterers. Furthermore, recent satellite radar sensors have a higher spatial resolution (down to 1 m), as well as a higher temporal frequency of image acquisitions (down to a few days). The coupling of the new algorithm with this new generation of satellites provides a valuable tool for monitoring the different phases of geothermal production and in support of the decision making process. Some examples from the US are presented here: the first case study involves the use of InSAR within a suite of tools for exploration of the San Emidio geothermal field in Nevada. This project aimed to develop geophysical techniques to identify and map large aperture fractures for the placement of new production/exploration wells. The second and third examples examine two zones in California: the Salton Sea area, where multi-interferogram InSAR provided an overview of surface deformation at a producing geothermal reservoir. Surface deformation in this area was complex, and the added detail provided insight into the interplay of tectonics and production activities. Additional InSAR studies have also been carried out at the Geysers field in order to evaluate the behavior of an Enhanced Geothermal System (EGS) in response to high rates of water injection, with a strong interest in researching induced seismicity and ground deformation. These studies, along with the continuing developments in radar satellite technology and in the field of InSAR, show considerable promise for the future monitoring of geothermal production facilities.