From site-scale to large areas monitoring of ground deformation phenomena by integration of different DInSAR techniques in Crotone Province (Southern Italy)

One of the most significant aims of this research project has been to apply SAR methods for the monitoring, the investigation and the evaluation of ground deformation phenomena in the Crotone province (Southern Italy). In detail, landslides and subsidence are the most remarkable and dangerous natural hazards in the study area, affecting people, buildings and main infrastructures. The intention was to show the potential of Differential Interferometry SAR (DInSAR) techniques for the detection and the estimation of the velocities and of the deformation of surface displacements, both on very local scale (slope scale) and on wide areas (kilometre-size extension). Such aim is achievable through the integration of DInSAR techniques along with conventional monitoring tools. The general idea of the project has been to assess the landslide hazard in selected areas of the Crotone province and to update the related landslide inventory map of the area, dated back to 2006, by means of DInSAR techniques. These goals have been reached through the comprehension and the understanding of the movements, on one hand on a very local scale (slope), and on the other hand, on a wide-area scale (the whole Crotone province). Additionally, two other case studies of subsidence, originated by different sources, have been studied with interferometry techniques, showing the suitability of such methods for other types of ground deformation. Several Multi Temporal Interferometry (MTI, Wasowski & Bovenga, 2014) approaches have been here applied, in order to investigate and analyze displacements present in the area, and the integration with “conventional” methods, such as inclinometers, piezometers and geomorphological surveys, turned out to be relevant for these purposes, providing very precise information about the nature and causes of ground deformation

PS-driven inventory of town-damaging landslides in the Benevento, Avellino and Salerno Provinces, southern Italy

The Apennine provinces of Campania Region (southern Italy), Benevento, Avellino and Salerno, are known for their 'unstable towns' suffering periodic damage from landslides. Their identification and mapping are very challenging tasks, since boundary mapping under urban settlements is not always possible without time-consuming field analysis of building damage and/or expensive mid-term diffuse ground-surface deformation monitoring. To overcome this problem, an inventory of town-damaging landslides, guided by available Permanent Scatterers (PS) ground-deformation data, was prepared. It provides an updated tool suitable to guide future land planning and historical site restoration in the Apennine provinces of Campania Region. Our fourteen Map Sheets show active and local reactivation of suspended/dormant landslides. Overall, 356 landslides were identified, amongst which 162 were identified as flows, 101 as slides, 1 as a spreads and 92 as complex landslides. To supplement our maps, a simplified distribution analysis based on major landslide morphometric characteristics was completed

Monitoring of remedial works performance on landslide-affected areas through ground- and satellite-based techniques

Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques have repeatedly proved to be an effective tool for built environments monitoring in areas affected by geological hazards. This paper describes how the Coherent Pixel Technique (CPT) approach has been successfully applied to assess the response of an unstable slope to the different phases of remedial works following a landslide event. The CPT technique was performed on 59 COSMO-SkyMed images obtained between May 2011 and August 2016 and centred on the Quercianella settlement (a small hamlet of Livorno municipality, Tuscany, Italy), where the reactivation of a dormant shallow slide had occurred in March 2011 and, hereafter, a geotechnical intervention, designed with the aim of mitigating the risks, has been conducted from August 2013, lasting thirteen months. The time series of CPT results show a deformation pattern with sudden accelerations (up to 21 mm in few months) corresponding to the beginning of the interventions, during which the area has been excavated to install a drainage well, followed by mild decelerations resulting from the stabilization of the area after the conclusion of the works. In particular, the integration of ground-based subsurface monitoring (inclinometers and piezometers) and DInSAR superficial data has provided consistent results for landslide characterization and helped defining the state of activity and the areal distribution of the sliding surface. Moreover, the performance of remedial works in the landslide-affected area has been observed, showing stabilization in the upper part of the hamlet and the ongoing movement in the lower part. The combined monitoring system also led the geotechnical company in charge of remedial works to design further stabilization works in order to preserve buildings and roads in the moving area. Therefore, the integration of remote sensing techniques and in situ instruments represents a timely and cost-efficient solution for intervention works monitoring, opening new perspectives on designing engineering solutions for the stabilization of unstable slopes

Post-failure evolution analysis of a rainfall-triggered landslide by multi-temporal interferometry SAR approaches integrated with geotechnical analysis

Persistent Scatterers Interferometry (PSI) represents one of the most powerful techniques for Earth's surface deformation processes' monitoring, especially for long-term evolution phenomena. In this work, a dataset of 34 TerraSAR-X StripMap images (October 2013–October 2014) has been processed by two PSI techniques - Coherent Pixel Technique-Temporal Sublook Coherence (CPT-TSC) and Small Baseline Subset (SBAS) - in order to study the evolution of a slow-moving landslide which occurred on February 23, 2012 in the Papanice hamlet (Crotone municipality, southern Italy) and induced by a significant rainfall event (185 mm in three days). The mass movement caused structural damage (buildings' collapse), and destruction of utility lines (gas, water and electricity) and roads. The results showed analogous displacement rates (30–40 mm/yr along the Line of Sight – LOS-of the satellite) with respect to the pre-failure phase (2008–2010) analyzed in previous works. Both approaches allowed detect the landslide-affected area, however the higher density of targets identified by means of CPT-TSC enabled to analyze in detail the slope behavior in order to design possible mitigation interventions. For this aim, a slope stability analysis has been carried out, considering the comparison between groundwater oscillations and time-series of displacement. Hence, the crucial role of the interaction between rainfall and groundwater level has been inferred for the landslide triggering. In conclusion, we showed that the integration of geotechnical and remote sensing approaches can be seen as the best practice to support stakeholders to design remedial works.Peer ReviewedPostprint (author's final draft

Assessment of building behavior in slow-moving landslide-affected areas through DInSAR data and structural analysis

Slow-moving landslides are a natural hazard which affects wide areas in the world and often are cause of significant damage to structures and infrastructures. Analysis of landslide evolution and of their interaction with existing man-made structures plays a key role in risk prevention and mitigation activities. To this purpose, a considerable interest towards innovative approaches has grown among the scientific community and land management institutions. In this work, Synthetic Aperture Radar data acquired by C-band and X-band sensors, combined with numerical analyses, have been successfully applied as a tool to detect spatial and temporal landslide-induced effects, in terms of deformations and structural behavior of a building affected by ground instability. Such approach has been applied to Moio della Civitella urban settlement (Salerno province, Italy), whose whole territory is interested by several slow-moving landslides. In detail, performance of a masonry building aggregate and the efficacy of restoration works have been investigated through an integrated assessment of displacement time-series pre- and post-repair intervention, and structural analysis performed with numerical code. Historical DInSAR data have permitted firstly the interpretation of building displacement time-series corresponding to pre- and post-works configurations; subsequently, the analysis of interpolated interferometric products has allowed to define gradient maps of vertical and horizontal displacements and to identify part of aggregate which can suffer a greater susceptibility to damage as a consequence of deformation gradients. Finally, the comparison of satellite and numerical data showed a substantial agreement with local failures and damage surveyed, thus confirming the capability of DInSAR technique to investigate building performance where no in situ displacement measurements were available.Research funded by the Campania Region through Regional Law n. 5/2002, year 2008 – Project “La pericolosità delle frane intermittenti in formazioni strutturalmente complesse; analisi comparata dei parametri geologici, mineralogici e geotecnici” (CUP_E64G08000060002) – Scientific manager: prof. Domenico Calcaterra. Part of this work was partially supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), the State Agency of Research (AEI) and the European Funds for Regional Development (FEDER) under projects TEC2017-85244-C2-1-P and TIN2014-55413-C2-2-P and the Spanish Ministry of Education, Culture and Sport under project PRX17/00439

From site-scale to large areas monitoring of ground deformation phenomena by integration of different DInSAR techniques in Crotone Province (Southern Italy)

One of the most significant aims of this research project has been to apply SAR methods for the monitoring, the investigation and the evaluation of ground deformation phenomena in the Crotone province (Southern Italy). In detail, landslides and subsidence are the most remarkable and dangerous natural hazards in the study area, affecting people, buildings and main infrastructures. The intention was to show the potential of Differential Interferometry SAR (DInSAR) techniques for the detection and the estimation of the velocities and of the deformation of surface displacements, both on very local scale (slope scale) and on wide areas (kilometre-size extension). Such aim is achievable through the integration of DInSAR techniques along with conventional monitoring tools. The general idea of the project has been to assess the landslide hazard in selected areas of the Crotone province and to update the related landslide inventory map of the area, dated back to 2006, by means of DInSAR techniques. These goals have been reached through the comprehension and the understanding of the movements, on one hand on a very local scale (slope), and on the other hand, on a wide-area scale (the whole Crotone province). Additionally, two other case studies of subsidence, originated by different sources, have been studied with interferometry techniques, showing the suitability of such methods for other types of ground deformation. Several Multi Temporal Interferometry (MTI, Wasowski & Bovenga, 2014) approaches have been here applied, in order to investigate and analyze displacements present in the area, and the integration with “conventional” methods, such as inclinometers, piezometers and geomorphological surveys, turned out to be relevant for these purposes, providing very precise information about the nature and causes of ground deformation

Slow-moving landslide monitoring with multi-temporal TerraSAR-X data by means of DInSAR techniques in Crotone Province (Southern Italy)

Surface movements and landslides monitoring with satellite-based DInSAR techniques is becoming more and more widespread among research groups and scientific community. The SAR Differential Interferometry (DInSAR) is one of the most powerful devices for monitoring deformation processes on the Earth surface. Here, a dataset of TerraSAR-X StripMap imagery covering almost the whole Crotone province territory, located in the south of the Italian peninsula, has been selected. The time span goes from April 2008 to June 2010 and from August 2013 to October 2014. Crotone province is severely affected by landslide phenomena, due to the geological and geomorphological context, as well as to the physical and mechanical properties of the involved materials. According to an accurate bibliographic and newspaper research, in agreement with field surveys, as to find the most suitable cases for the use of the satellite interferometry, different case studies have been selected. Hence, the attention has been concentrated on several urban settlements. The most important are Papanice, Cutro, Santa Severina, San Mauro Marchesato, Cirò, Crucoli, in which, several landslide evidences, affecting roads and buildings, have been recognized. Particular attention has been focused on slow and intermittent landslides, highly detectable by DInSAR techniques. In this work, two different multitemporal interferometry (MTI – Wasowsky et al., 2014) approaches and two different software packages have been used and compared in order to identify benefits/constraint of each MTI approach and each software. Such approaches are: a) the “permanent” (or “persistent”, or “point-like”) scatterers (PS - Ferretti et al., 2001) and the “small baseline subset approach” (SBAS - Berardino et al., 2002; Lanari et al., 2004) implemented both in the SARscape software, developed by the SARMAP team, and on SUBSOFT processor, this last based on the Coherent Pixel Technique (CPT - Mora et al., 2003, Blanco et al., 2008), developed by the Remote Sensing Laboratory (RSLab) group, from the Universitat Politècnica de Catalunya (UPC). For every technique, displacement time series have been obtained and compared. The interferometric analysis has shown good results, being able to identify displacement rates up to 4 cm/year, and also allowing to redraw landslide boundaries, previously identified in the Hydrogeological Setting Plan of the Calabria region (2001), updating their state of activity, as well. Moreover, being the available dataset antecedent to the landslides’ reactivations, the adopted DInSAR techniques have been able to recognize precursor stages of slope failures, hence confirming the reliability of SAR methods as powerful monitoring and prediction tools

Preliminary results of a geomorphological and DInSAR characterization of a recently identified Deep-Seated Gravitational Slope Deformation in Sicily (Southern Italy)

The study is part of a larger project that involves the analysis of recently identified Deep-Seated Gravitational Slope Deformation (DSGSD) in Sicily which have been sub-divided according to the geological framework in light of the new geological data about the regional setting. Here are presented the first results of a multidisciplinary study of a DSGSD recently identify in Mount San Calogero area (Northern Sicily). The study was performed by means of different approaches including conventional methods (field surveys) and the Differential Interferometry Synthetic Aperture Radar (DInSAR) technique. The geological and geomorphological analyses were carried out to investigate slopes dynamic, and DInSAR analysis were integrated to obtain, for the first time in this area, displacement rates of the DSGSD. The identified deformation patterns show the effective movement of homogeneous rock mass that constitutes the Mount San Calogero, characterized by the gravitational morphostructures and evidence of slopes deformation, as well as the shallow landslides detected in the foothill area. Furthermore, the distribution of the Persistent Scatterers (PS) points shows a clear convergence with the main tectonic lineaments of the area, thereby emphasizing the role of the structural setting in the DSGSD's development

Implementation of DInSAR methods for the monitoring of heritage sites: Hera Lacinia in Crotone (Southern Italy)

Deformation and generally ground displacement can also affect cultural and archeological heritage sites: the monitoring of such ancient witnesses results to be very significant for the preservation and the conservation of the structures present within the sites. The Differential SAR interferometry is here applied to investigate the displacements occurring in Capo Colonna area (Crotone municipality, Southern Italy), a site which name derives from the only remaining column of the old Hera Lacinia temple, belonging to the Magna Graecia city of Kroton. The processing and the interpretation of SAR images has been carried out thanks to the availability of stacks of TerraSAR-X imagery, in the time span 2008-2010 and of COSMO Sky-Med acquired between 2014-2015. The results obtained show the protraction of a well-known subsiding trend, probably caused by a mix of natural causes (lithostratigraphic setting, seismic activity, eustatic sea-level changes), and anthropic causes, represented by the on-shore and off-shore gas extraction active in the area, identifying displacement velocities up to 15 mm/yr along the Line of Sight of the satellite, both in the ascending and in the descending orbits. These two contributions have been assembled in order to obtain the total vertical displacement, which has been calculated in 3 cm in two years of analysis. Moreover, the installation of 80 corner reflectors in October 2014 provided an improvement of the SAR interpretation, allowing also to focus in the future also on the coastal erosion affecting the site and the ruins and to further investigate about the relationship between gas extraction, performed by ENI, and the vertical motion

Multivariate Statistical approach vs. Deterministic physically based model for landslide susceptibility assessment

We present a comparison between the results of two landslide susceptibility analyses approaches: multivariate (Logistic Regression) and deterministic–physically based (SHALSTAB). In order to assess the Landslide Susceptibiliy Index, five different predisposing factors to landslide occurrence (slope, aspect, land cover, distance to streams and rocky scarps) for the first one and material density, material friction angle, material hydraulic transmissivity, bulk cohesion and depth to potential shear plane for the second have been set up respectively. Two different sectors of the urban area of the Phlegraean Fields, within the municipalities of Naples and Pozzuoli, have been selected for the application of the two methodologies: the Agnano Plain hillslopes (slope maximum elevation: 190 m a.s.l.) and the Astroni volcano (max. elev.: 253 m a.s.l.). The results have been compared and tested (ROC/AUC curves) allowing further considerations about the benefits and the constraints of each model