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Caratterizzazione e modellazione di fenomeni geologici di instabilità attraverso tecniche di telerilevamento satellitare e simulazioni numeriche
Full text linkAnalyses of ground displacements can help to define the evolution of areas affected by instability phenomena and identify their triggering factors. To this end, Synthetic Aperture RADAR (SAR) satellite data can be used to collect direct measurements of superficial deformations in instability-prone areas. Results from remote sensing analyses can be then compared with outcomes from numerical simulations, and in particular with displacement or velocity fields, to validate numerical modeling and eventually recalibrate the simulation of instabilities, predisposing and triggering conditions.
Numerical simulations allow reproducing slope behavior under some hypotheses but their accuracy is strongly connected to the amount of available input data. Most of the required parameters can be set based on reasonable assumptions that consequently can be verified through classical field tools and geological survey or remote sensing techniques.
Direct or remote sensing techniques can be used to characterize and monitor ground deformation phenomena, and particularly to identify surface displacements. These information can be used to verify the suitability of numerical model predictions and the adequacy of preliminary hypotheses.
An innovative approach could consider a surface displacement map, as the starting point to re-create a model of instability phenomena. This application requires precise velocity data characterized by an adequate resolution, depending on the phenomenon analyzed. Recently this method was applied to earthquakes with satisfying results (Wright at al., 2006).
This work is aimed to determine which is the contribution of SAR satellite data in investigating instabilities phenomena, in particular landslides and sinkholes. This methodological approach was tested in different conditions to understand its applicability and how to optimize the results overcoming some of the observed limits.
Satellite remote sensing techniques have shown to lead to accurate large-scale surface displacement mapping. Specifically “Interferometric Synthetic Aperture RADAR” (InSAR) technique allows to measure accurate land displacement. Furthermore, not only deformation but even the evolution of displacements can be estimated, combining InSAR information from a large number of SAR images and analyzing changes on the signal phase. This technique is defined D-InSAR (Differential Interferometric SAR) and PS InSAR (Ferretti et al., 2001) and SBAS techniques (Berardino et al., 2002) represent the main methodology proposed. But D-InSAR techniques have some limits of applicability. For example, due to high RADAR viewing angles, the current space-borne systems can detect only a fraction of the horizontal component of the movement. In fact not every geometrical configurations and slope exposition can be surveyed. Further problems are connected with the presence of dense vegetation. In these situations amplitude can be exploited to identify surface deformations (Casu et al., 2011).
Applying the above mentioned techniques it is possible to observe deformation patterns and surface movements. Comparing displacement obtain from monitoring stage with results from numerical modeling, let to understand if numerical prevision is satisfying and the evolution of deformations is correct.
The contribution of SAR data in numerical simulation of ground deformations was tested in landslide, subsidence and sinkhole - prone areas, located in the piedmont sector of North-Eastern Italian Alps and in the Jordanian coast of the Dead Sea.
The first case study is Val Maso landslide, located in Valli del Pasubio municipality, which was triggered by an exceptional flood event occurred in November 2010.
A back stability analysis was carried out to evaluate the geotechnical properties of the involved materials. Then, parameters from back analysis were used in a uncoupled seepage and slope stability analysis of the area behind the main scarp to forecast the effects of hydrological conditions due to different rainfall depths, i.e. to identify the minimum rainfall threshold for triggering the retrogression of the phenomenon.
Some more information about this phenomenon have been searched, analysing a stacking of RADAR satellite images. Because of the dense vegetation and the aspect of the area, outcomes of PS and SBAS DInSAR technique were not satisfying.
That is why SAR data were analyzed concentrating on amplitude changes of the signal instead on studying the phase. A stack of nine COSMO-SkyMed images, acquired over the 2010 event, were used. Amplitude changes were evaluated. Results showed it is possible to detect the effect of ground deformations from the data analyzed and to define the boundary of the landslide.
The second case study is Cischele landslide, located in Recoaro Terme municipality, which caused severe damages on the buildings and on the Provincial street after the rainfall event of November 2010.
This phenomenon is related to a reactivation of a instability whose behavior seems to be connected to climatic conditions.
Data obtained from field and laboratory analyses were used on the creation of a numerical model. Ground displacements of the slope were evaluated analyzing data obtained from PS available for Cischele area, obtained processing SAR images acquired by ERS and ENVISAT satellites, from May 1995 to May 2000 and from September 2004 to June 2010, respectively.
Ground velocity and displacements are measured along the line of sigh of the satellites. Only information obtained from descending orbits are available. Furthermore, InSAR images acquired by COSMO-SkyMed satellites over the event were analyzed. SBAS techniques was applied. Interferograms were generated using InSAR images and a 90 meters resolution Digital Elevation Model (DEM), SRTM DEM. 14 descending images were available from April 2010 to September 2012.
Unfortunately, variation in surface condition between two different acquisitions produces loss of coherence. This effect is strongly connected to the presence of vegetation in the area. It was possible to overcome this problem through an accurate calibration of the filtering parameters, extending the coverage of the final displacement map. Results showed a maximum velocity component of 12 mm/year.
Finally, DInSAR techniques were applied to investigate sinkholes affecting the Jordanian coast of the Dead Sea. The Dead Sea is a hyper saline terminal lake located in a pull-apart basin, which is one of the major components of the Jordan Dead Sea Transform fault system. Most of the area is characterized by highly karstic and fractured rock formations that are connected with faults. Karstic conduits extend from the land into the sea.
Since the 1960s, the Dead Sea level is dropping at an increasing rate: from about 60 cm/yr in the 1970s up to 1 m/yr in the 2000s. From about the mid-1980s, sinkholes appeared more and more frequently over and around the emerged mudflats and salt flats. Strong subsidence and landslides also affect some segments of the coast. Nowadays, several thousands of sinkholes attest that the degradation of the Dead Sea coast is worsening.
The deformation analysis is focused on Ghor Al Haditha area, located in the South-Eastern part of the lake coasts. SAR data acquired by three different sensors, ERS, ENVISAT and COSMO-SkyMed were processed.
70 ERS images from 1992 to 2009 and 30 ENVISAT images from 2003 to 2010 were processed. SBAS technique were applied to define surface velocity and displacement maps. Because of the resolution of these sensors, consisting on 25 m2, it was possible to clearly define areas affected by subsidence but the single sinkholes could not be detected because of the small size of each punctual event, that is generally varying from few meters to a hundred meters diameter.
Furthermore, SBAS was applied to 23 COSMO-SkyMed SAR satellite images from December 2011 to May 2013. The high resolution of these data (3m x 3m) and the short revisiting time allowed to have precise information of the displacement of punctual sinkholes beyond the overall subsidence of the coast. A specific sinkhole was considered to understand its temporal evolution.
On the basis of the results from D-InSAR processing, a simplified analytical model was implemented. Vertical and horizontal components of the surface displacement field obtained from analysis of SAR images have been used as input data to derive geometric parameters of the source and in particular to estimate the volumetric strain of the phenomenon. Position, dimension and mechanism were obtained.
The gained experience proved that space-borne SAR data allow to obtain important information about the dynamics of instability phenomena, which degree of precision depends on several factors, as vegetation density and surface velocity. The applicability of D-InSAR methods in different conditions was tested to obtain useful information to re-create the phenomena through numerical modeling.
When rapid displacements overcome the maximum detectable surface velocities between two consecutive SAR acquisitions and changing in land cover produces a complete coherence loss, the amplitude of the signal can be analyzed instead of the phase. In the Val Maso landslide, a rapid mapping of surface deformation was possible, providing important hints to manage post-event emergency situations.
Despite the dense vegetation in Cischele area, SBAS technique could assess a component of the landslide displacement, through an accurate calibration of some processing parameters.
Thanks to the flat morphology of the site and the almost absent vegetation covering, analysis of sinkholes in Jordan Dead Sea coast gave precise information about ground deformation and helpful data to model a sinkhole and to define its geometry and volume reduction. In these favorable conditions, SAR data allow one to predict the occurrence of geological instabilities, characterize their extension, model their evolution and define an early warning system to prevent catastrophic events
Phase and amplitude analyses of SAR data for landslide detection and monitoring in non-urban areas located in the North-Eastern Italian pre-Alps
No full textMonitoring and modeling of sinkholes affecting the Jordanian coast of the Dead Sea through satellite interferometric techniques
No full textUsing high resolution SAR data to monitor deformations at a very detailed scale
No full textThe detection and monitoring of deformation phenomena caused by natural and human-induced processes are increasingly performed through the analyses of Synthetic Aperture Radar (SAR) satellite data.
The use of Differential Interferometric SAR (DInSAR) techniques provides information about the temporal evolution of different events, such as earthquakes, volcano eruptions, subsidence and landslides. The recent availability of high resolution data, from COSMO-SkyMed and TerraSAR-X missions, led to important advances on the use of DInSAR techniques to monitor different types of phenomena, working on very detailed scales. The present work is aimed to test the response of the processing of COSMO-SkyMed images, with different DInSAR techniques, to analyse the fields of displacements induced by a sinkhole affecting the Jordanian coast of the Dead Sea and a recent building in Astana, Kazakhstan
Monitoring of sinkholes and subsidence affecting the Jordanian coast of the Dead Sea through Synthetic Aperture Radar data and last generation Sentinel-1 data
No full textSince the mid-1980s the coast of the Dead Sea is affected by sinkholes occurring over and around the emerged
mud and salt flats. Strong subsidence and landslides also affect some segments of the coast. Nowadays, several
thousands of sinkholes attest that the degradation of the Dead Sea coast is worsening. Furthermore, soil deformations
are interesting the main streets running along both the Israeli and Jordanian sides of the Dead Sea.
These hazards are due to the dramatic dropping of the Dead Sea level, characterized by an increasing rate from
about 60 cm/yr in the 1970s up to 1 m/yr in the 2000s, which provokes a lowering of the fresh-saline groundwater
interface, replacing the hypersaline groundwater with fresh water and causing a consequent erosion of the subsurface
salt layers. Subsidence, sinkholes, river erosion and landslides damage bridges, roads, dikes, houses, factories
worsening this ongoing disaster. One of the most emblematic effects is the catastrophic collapse of a 12-km newly
constructed dyke, located on the Lisan Peninsula (Jordan), occurred in 2000.
Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques and Advanced stacking DInSAR techniques
(A-DInSAR) were applied to investigate sinkholes and subsidence affecting the Jordanian coast of the Dead
Sea. The use of SAR data already proof to be efficient on the risk management of the area, allowing to identify a
vulnerable portion of an Israeli highway, averting a possible collapse.
Deformation analysis has been focused on the Ghor Al Haditha area and Lisan peninsula, located in the South-
Eastern part of the lake coast. The availability of a huge database of SAR data, since the beginning of the 90s,
allowed to observe the evolution of the displacements which are damaging this area. Furthermore, last generation
Sentinel-1 data, acquired by the ESA mission, were processed to obtain information about the recent evolution of
the subsidence and sinkholes affecting the study area, from the end of 2014 to the present. Important subsidence
can be noticed mainly in correspondence of the emerging coast. Moreover, some solar evaporation pools used
for salt production are injured by high deformations. Analysis of results obtained from SAR satellite data allows
to identify different hazard processing affecting the study area and define the displacement time-series to clearly
describe the evolution of the different phenomena, resulting as an effective tool to prevent damage and collapses.
Furthermore, vulnerability maps can be created and possible precursor behaviour can be highlighted demonstrating
the predictive capability of these data
Monitoring Mosul Dam Through Low And High-Resolution SAR Data
No full textStructural health assessment is an important practice to guarantee the safety of infrastructure in general. In case of dam monitoring, it is necessary to control the structure itself and the water reservoir, to guarantee efficient operation and safety of surrounding areas. Ensuring the longevity of the structure requires the timely detection of any behaviour that could deteriorate the dam and potentially result in its shutdown or failure. Traditional structural dam monitoring requires the identification of soil movements, tilt, displacements, stress and strain behaviour.
The detection and monitoring of surface displacements is increasingly performed through the analysis of satellite Synthetic Aperture Radar (SAR) data, thanks to the non-invasiveness of their acquisition, the possibility to cover large areas in a short time and the new space missions equipped with high spatial resolution sensors. The availability of SAR satellite acquisitions from the early 1990s enables to reconstruct the historical evolution of dam behaviour, defining its key parameters, possibly from its construction to the present. Furthermore, the progress on SAR Interferometry (InSAR) techniques through the development of Differential InSAR (DInSAR) and Advanced stacking techniques (A-DInSAR) allows to obtain accurate velocity maps and displacement time-series.
The importance of these techniques emerges when environmental or logistic conditions do not allow to monitor dams applying the traditional geodetic techniques. In such cases, A-DInSAR constitutes a reliable diagnostic tool of dam structural health to avoid any extraordinary failure that may lead to loss of lives.
In this contest, an emblematic case will be analysed as test case: the Mosul Dam, the largest Iraqi dam, where monitoring and maintaining are impeded for political controversy, causing possible risks for the population security. In fact, it is considered one of the most dangerous dams in the world because of the erosion of the gypsum rock at the basement and the difficult interventions due to security problems. The dam consists of 113 m tall and 3.4 km long earth-fill embankment-type, with a clay core, and it was completed in 1984. It started generating power on 1986.
Specific objective consists in determining the degree of detail of dam surface strains that can be obtained from different satellite SAR datasets at different resolutions (microwaves X and C bands). Therefore, different datasets are analysed: the archive available SAR data (ERS and Envisat from ESA), the currently acquiring Sentinel data (EU Copernicus programme) and the high-resolution COSMO-SkyMed data (ASI program) over the study area (Mosul dam).
The different stacks of data are processed applying SBAS and PS A-DInSAR techniques; the deformation fields obtained from SAR data are evaluated to assess the temporal evolution of the strains affecting the structure. Obtained results represent the preliminary stage of a multidisciplinary project, finalized to assess possible damages affecting a dam through remote sensing and civil engineering surveys
Use of Sentinel-1 SAR data to monitor Mosul dam vulnerability
No full textThe structural monitoring of dams is an important practice to guarantee their safety. Moreover, the water reservoir
and the efficient operation and safety of surrounding areas need to be monitored. Considering the importance
of large dams as multipurpose infrastructure for flood control, energy production, water supply and irrigation,
ensuring their longevity is a key aspect on their management. Therefore, it is of great importance to detect dam
deterioration potentially resulting in its shutdown or failure, preventing life and economic losses. Traditional dam
monitoring requires the identification of soil movements, tilt, displacements, structural stress and strain behaviour.
Since the ’90, innovative remote sensing techniques based on satellite Synthetic Aperture Radar (SAR) data
were developed to detect and monitor surface displacements. The main advantages of SAR data are the noninvasiveness
of their acquisition, the possibility to cover large areas in a short time and the advancement. Moreover,
the availability of SAR satellite acquisitions from the 1990s enables to reconstruct the historical evolution of dam
behaviour. Furthermore, the use of SAR Interferometry (InSAR) techniques, Differential InSAR (DInSAR) and
Advanced stacking techniques (A-DInSAR), produce accurate velocity maps and displacement time-series. The
importance of these techniques emerges when environmental or logistic conditions do not allow to monitor dams
applying the traditional geodetic techniques.
An iconic case demonstrating the relevance of remote sensing observations is the Mosul Dam, the largest Iraqi
dam, where monitoring and maintaining are impeded for political controversy, thus the risk for the population is
very high. It is considered one of the most dangerous dams in the world because of the erosion of the gypsum
rock at the basement and the difficult interventions due to security issues. It consists of 113 m tall and 3.4 km long
earth-fill embankment-type, with a clay core. It was completed in 1984 and started generating power on 1986.
Since then, frequent consolidation works have been carried out pumping cement mixtures into the soil foundation
to keep it stable and prevent it from sinking and then breaking apart.
To overcome the impossibility of directly monitoring the structure, analysis of recent deformation affecting
the Mosul dam is achieved considering C-band Sentinel-1 SAR data, acquired from the end of 2014 to the
present. These 20-m ground resolution data can provide a millimetric precision on displacements. Furthermore,
ESA archive available SAR data (ERS and Envisat) are considered to reconstruct the temporal evolution of the
deformations.
In this work, different stacks of data are processed applying SBAS and PS A-DInSAR techniques; deformation
fields obtained from SAR data are evaluated to assess the temporal evolution of the strains affecting the structure.
Obtained results represent the preliminary stage of a multidisciplinary project, finalised to assess possible damages
affecting a dam through remote sensing and civil engineering surveys
Using PS-InSAR data to evaluate temporal evolution of instability phenomena: the case study of Cischele landslide (North-Eastern Italian Alps)
No full textFloating anchors in landslide stabilization: the Cortiana case in North-Eastern Italy
No full textIn order to reduce the cost of landslide stabilization works, often very high, we are always looking for new effective and more economical solutions. This work re-ports the case of a landslide occurred in November 2010 in the Cortiana locality (Vicenza, Italy). After a brief analysis of occurrence conditions and characteristics of the landslide, the paper presents the most important results of analyses carried out in order to design and evaluate the efficiency of some innovative interventions performed in the area, which allowed a complete slope stabilization
Subsidence zonation through satellite interferometry in coastal plain environments of ne italy: A possible tool for geological and geomorphological mapping in Urban Areas
Full text linkThe main aim of this paper is to test the use of multi-temporal differential interferometric synthetic aperture radar (DInSAR) techniques as a tool for geological and geomorphological surveys in urban areas, where anthropogenic features often completely obliterate landforms and surficial deposits. In the last two decades, multi-temporal DInSAR techniques have been extensively applied to many topics of Geosciences, especially in geohazard analysis and risks assessment, but few attempts have been made in using differential subsidence for geological and geomorphological mapping. With this aim, interferometric data of an urbanized sector of the Venetian-Friulian Plain were considered. The data derive by permanent scatterers InSAR processing of synthetic aperture radar (SAR) images acquired by ERS 1/2, ENVISAT, COSMO SKY-Med and Sentinel-1 missions from 1992 to 2017. The obtained velocity maps identify, with high accuracy, the border of a fluvial incised valley formed after the last glacial maximum (LGM) and filled by unconsolidated Holocene deposits. These consist of lagoon and fluvial sediments that are affected by a much higher subsidence than the surrounding LGM deposits forming the external plain. Displacement time-series of localized sectors inside the post-LGM incision allowed the causes of vertical movements to be explored, which consist of the consolidation of recent deposits, due to the loading of new structures and infrastructures, and the exploitation of the shallow phreatic aquifer
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