Advanced radar-interpretation of InSAR time series for mapping and characterization of geological processes

We present a new post-processing methodology for the analysis of InSAR (Synthetic Aperture Radar Interferometry) multi-temporal measures, based on the temporal under-sampling of displacement time series, the identification of potential changes occurring during the monitoring period and, eventually, the classification of different deformation behaviours. The potentials of this approach for the analysis of geological processes were tested on the case study of Naro (Italy), specifically selected due to its geological setting and related ground instability of unknown causes that occurred in February 2005. The time series analysis of past (ERS1/2 descending data; 1992–2000) and current (RADARSAT-1 ascending data; 2003–2007) ground movements highlighted significant displacement rates (up to 6 mm yr<sup>−1</sup>) in 2003–2007, followed by a post-event stabilization. The deformational behaviours of instable areas involved in the 2005 event were also detected, clarifying typology and kinematics of ground instability. The urban sectors affected and unaffected by the event were finally mapped, consequently re-defining and enlarging the influenced area previously detected by field observations. Through the integration of InSAR data and conventional field surveys (i.e. geological, geomorphologic and geostructural campaigns), the causes of instability were finally attributed to tectonics

Ground deformation and associated hazards in NW peloponnese (Greece)

In the last decades, ground deformations were investigated, analysed and monitored using several methods. As a consequence of a spreading urbanization, several phenomena, e.g. landslide and subsidence, were emphasized or triggered causing not only socio-economic damages, but, in some cases, also casualties. The investigation and mapping of these phenomena are important for both local authorities and civil protection in order to promote a higher conscientious urban planning and to highlight the more hazardous areas. Furthermore, the information are a key point for social development connected to the awareness of the environment and the related risk. The Achaia prefecture, in the north-eastern Peloponnese (Greece), close to the Gulf of Patras, is an area strongly affected by subsidence and landslides. Furthermore, this is an earthquake-prone area, a factor that can trigger some mass movements. For this region, a landslide inventory was realized with the help of the interpretation of Persistent Scatterers data, for the period 1992–2008, and high-resolution optical satellite images, available until 2016, in addition to the investigation of the landslide State of Activity. Moreover, for the coastal area, a section was investigated to evidence subsidence

Use of PSInSAR data to map highly compressible soil layers

A new approach to the use of Persistent Scatterers (PS) Interferometry data in the reconstruction of the extension of compressible geological bodies is presented. The methodology was applied in the test area of the Tiber River delta (Italy), characterized by the presence of two large marshy zones, known as the Maccarese and Ostia Antica ponds. PSInSARâ\u84¢ data, derived from ERS1/2, ENVISAT and RADARSAT-1 images, and spanning a time interval between 1992 and 2006 were used to verify the possibility to reconstruct the spatial distribution of the peat levels inside the Maccarese and Ostia Antica ponds. Borehole information was analyzed to calibrate the InSAR data and the deformation rates were used to hypothesize the presence of a thick compressible layer where geological information is lacking. Variations in deformation rates registered by the single PS were assumed to be representative of a variation in the stratigraphic asset. The obtained results demonstrate that this approach could be satisfactorily used to investigate wide areas in a short time, reducing the number of boreholes to drill, and it could be a complementary technique to obtain information about the 2D geometry of specific geological levels

New, simplified and improved interpretation of the Vaiont landslide mechanics

Both the occurrence and behaviour of the Vaiont landslide have not been satisfactorily explained previously because of difficulties arising from the assumption that the failure surface was ‘chair’ shaped. It is now known that there was no ‘chair’, which means that the 1963 landslide could not have been a reactivated ancient landslide because the residual strength of the clay interbeds would have been insufficient for stability prior to 1963. Furthermore, the moderately translational geometry reduces the influence of reservoir-induced groundwater and hence of submergence. Standard stability analyses now show that prior to 1960, the average shear strength must have significantly exceeded the peak shear strength of the clay interbeds known to have formed the majority of the failure surface. Three-dimensional stability analyses confirm these results and show that at the time of the first significant movements in 1960, the rising reservoir level had a negligible effect on the Factor of Safety. According to these results, the Vaiont landslide was most likely initiated by pore water pressures associated with transient rainfall-induced ‘perched’ groundwater above the clay layers, in combination with a smaller than hitherto assumed effect of reservoir impounding, then developed by brittle crack propagation within the clay beds, thus displaying progressive failure. Further, very heavy rainfall accelerated the process, possibly due to reservoir-induced groundwater impeding drainage of the rainwater, until the limestone beds at the northeast margin failed. With the shear strength suddenly reduced to residual throughout, the entire mass was released and was able to accelerate as observed

Monitoring landslide-induced deformation with TerraSAR-X Persistent Scatterer Interferometry (PSI) : Gimigliano case study in Calabria Region (Italy)

Landslide phenomena represent a major geological hazard worldwide, threatening human lives and settlements, especially in urban areas where the potential socio-economic losses and damages are stronger because of the higher value of the element at risk exposure and vulnerability. The impact of these natural disasters in highly populated and vulnerable areas can be reduced or prevented by performing a proper detection of such ground movements, in order to support an appropriate urban planning. Mapping and monitoring of active landslides and vulnerable slopes can greatly benefit from radar satellite data analysis, due to the great cost-benefits ratio, non-invasiveness and high precision of remote sensing techniques. This work illustrates the potential of Persistent Scatterer Interferometry (PSI) using X-band SAR (Synthetic Aperture Radar) data for a detailed detection and characterization of landslide ground displacements at local scale. PSI analysis is a powerful tool for mapping and monitoring slow surface displacements, just particularly in built-up and urbanized areas where many radar benchmarks (the PS, Persistent Scatterers) are retrieved. We exploit X-band radar data acquired from the German satellite TerraSAR-X on Gimigliano site located in Calabria Region (Italy). The use of TerraSAR-X imagery significantly improves the level of detail of the analysis and extends the applicability of space-borne SAR interferometry to faster ground movements, due to higher spatial resolutions (up to 1 m), higher PS targets density and shorter repeat cycles (11 days) of X-band satellites with respect to the medium resolution SAR sensors, such as ERS1/2, ENVISAT and RADARSAT1/2. 27 SAR scenes were acquired over a 116.9 Km2 extended area from the satellite TerraSAR-X in Spotlight mode, along descending orbits, with a look angle of 34°, from November 2010 to October 2011. The images were processed by e-GEOS with the Persistent Scatterers Pairs (PSP) technique, providing the estimation of annual velocities of LOS (Line Of Sight) ground displacements and related deformation time series for the whole acquisition period. The methodology performed is based on the integration of recent radar PS data in X-band with historical SAR archives derived from ERS1/2 and ENVISAT data in C-band, and with geological and geomorphological evidences resulting from the existing auxiliary data (e.g. landslide databases, thematic maps and aerial orthophotos), finally validated with field checks and in situ observations in the study area. This operative procedure led to the detailed study of the spatial distribution and temporal evolution of ground movements phenomena in Gimigliano site. The outcomes of this work represent a valuable example of detection and characterization of landslide-induced phenomena identified in detail by PSI analysis in X-band at local scale. This approach showed that PSI technique has the potential to improve the quality and timeliness of landslide inventories and consequently help for the implementation of best strategies for risk mitigation and urban-environmental design. This work was carried out within the SAFER (Services and Applications For Emergency Response) project, funded by the European Commission within the 7th Framework Programme under the Global Monitoring for Environment and Security (EC GMES FP7) initiative

Monitoring, prediction, and early warning using ground-based radar interferometry

In order to define adequate prevention measures and to manage landslide emergencies, real-time monitoring is required. This paper presents two different applications of the remote sensing technique: the ground-based synthetic aperture radar interferometry, here proposed as a monitoring and early warning support for slope instability. Data acquisitions carried out through a ground-based synthetic aperture radar interferometer, operating in Ku band, installed in front of the observed slopes, are discussed. Two case studies, based on the use of the same apparatus (formerly developed by the Joint Research Center of the European Commission and by Ellegi-LiSALab srl), are reported: the first one concerns the monitoring of a large landslide, named Ruinon (Valfurva, Italy). The second one deals with the monitoring of the NW unstable slope in the Stromboli island aimed to implementing an early warning system. Acquired interferometric data are processed to provide displacements and velocity maps of the monitored area. The monitoring services ongoing on the Ruinon landslide and on Stromboli demonstrate the capability of this technique to operate in different operative settings (i.e., different phenomena and geological framework) and for different aims (monitoring for prevention, early warning, and emergency assessment). This methodology has also been proved by national and regional authorities of civil protection in order to provide a real-time monitoring for emergency management. \ua9 Springer-Verlag 2010