L. Guerri

Space‐borne and ground‐based SAR interferometry as tools for landslide hazard management in civil protection

In recent years, SAR interferometry has become one of the most popular emerging techniques for the assessment of ground displacements, and, as such, it is of great interest as a possible operational tool for civil protection institutions having to deal with landslide risk. The paper presents some of the results obtained in northern Italy during a research project aimed at testing the potentiality of the application of C‐band space‐borne interferometry and Ku‐band ground based interferometry during different specific civil protection activities. Main research objectives were the detection of the movements of complex earth and rock slides affecting built‐up areas during the 1990s, and the near real‐time monitoring of a reactivated rotational earth slide over an emergency period of 15 days. Results of space‐borne interferometry did qualitatively fit with the geological interpretation of the mass movements and with ground truths such as damaged buildings and in situ monitoring systems. However, this was not achieved in quantitative terms, suggesting that this technique should be used limitedly for displacement recognition and not monitoring. On the other hand, ground‐based interferometry proved valuable both for a qualitative and a quantitative estimate of slope movements. Nonetheless, the research has also enabled the limitations that are still to be tackled in order to bring these systems to an operational usage in civil protection to be highlighted.

SAR interferometry from satellite and ground-based system for monitoring deformations on the Stromboli volcano

After the collapse of a landslide of 20 million m/sup 3/ from the NE slope of the Stromboli volcano and the subsequent tsunami at the end of December 2002, a ground-based InSAR system (interferometric synthetic aperture radar) was installed on the flank of the Sciara del Fuoco, a collapse depression formed 5 million BP. Through the radar measurement it has been possible to assess the deformation field over a large portion of the target area and to differentiate different processes. Twelve months of radar monitoring have permitted to follow the temporal and spatial evolution of the mass movement in the Sciara. The landslide showed wide fluctuations in the displacement rate, between 0.6 and 10 mm/h, with acceleration phases coinciding with episodes of more intense effusive activity. The dynamic of the volcano has been also studied through the use of DInSAR from satellite platform. Different images acquired from the ERS2 satellite before and after the collapse of the landslide have been interferometrically processed in order to extract information about the ground deformation occurred on the island due to the volcanic activity.

Ground Deformation from Ground‐Based SAR Interferometry

An in-depth analysis of the last two images acquired by the ground-based interferometric synthetic aperture radar system installed on Stromboli before the 5 April 2003 explosion allowed us to detect the precursory signals of the explosion related to ground deformation. In particular, it was possible to estimate the exact time of the explosion through the time domain analysis of raw data from the radar acquisition. This was interrupted by a blackout that occurred a few seconds after the event. The explosion onset time corresponds to a clear change in the intensity of the backscattered energy, related to the dense volcanic plume emission from the Crater. In addiction, the use of a particular interferometric processing technique for the last two acquisitions, consisting of the selection of synthetic sub-apertures from the main ones and creating with these a sequence of interferograms with a higher temporal resolution, detected precursory deformations starting 2 min before the explosion. These observations indicate the occurrence of an elastic deformation of a centimeter amplitude that affected the volcanic edifice progressively from the Crater down to the Sciara del Fuoco depression.

On the Use of Ground-Based SAR Interferometry for Slope Failure Early Warning: the Cortenova Rock Slide (Italy)

This contribution illustrates the capabilities of groundbased SAR interferometry (GBInSAR) to be used as an early warning for the detection of precursory ground displacements that can suggest the imminent occurrence of a slope failure. SAR data were acquired by a ground-based SAR system, belonging to the LISA interferometer series designed by the Joint Research Centre of the European Commission, over the Cortenova rock slide (Regione Lombardia, Italy) and interferometrically analyzed in near-real time. The system was used to provide, during the 2002–2003 emergency caused by the landslide reactivation, the civil protection authorities with an operational tool for the assessment of the mass movement temporal evolution. After the main rupture occurred at the beginning of December 2002, which caused severe damage to the Bindo Village, destroying several houses and factories, interrupting one key connection road and partially damming a river, concern over the occurrence of further collapses of the still unstable slope led to the evacuation of 900 people living close to the run-out area. Such a situation induced the civil protection authorities to arrange a real-time monitoring system. Measurements of ground displacements continuously collected by the radar system up to May 2003, besides detecting the portions of the slope affected by movement, revealed the gradual deceleration of the residual movements passing from 5 cm d−1 to 0.3 cm d−1.

Microwave interferometric sensors as a tool for space and time analysis of active volcano deformations: The Stromboli case

A Ground Based SAR Interferometer (GB-InSAR) was installed at Stromboli volcano (Italy) in February 2003 to continuously monitor the behaviour of the morphological depression known as Sciara del Fuoco, SdF, with alerting purposes. This was decided as a consequence of the collapse of a large landslide from the NW slope of the SdF and the subsequent tsunami occurred on December 2002. The GB-In SAR system, working at Ku band, was set up on the stable right flank of the SdF; it has been continuously working and during this last five years has permitted to follow the temporal and spatial evolution of the mass movement in the SdF and the crater. Interferometric maps have permitted to assess the deformation field over a large portion of the target area and to characterize different processes. The system allowed to observe in particular two main events occurred on 5 April 2003 (a major explosion) and on 27 February 2007 (beginning of the effusive phase) respectively. The potential of the use of DInSAR from satellite platforms working at C band to understand the dynamic of the whole volcano has been also investigated. Different images acquired from the ERS2, RADARSAT and ENVISAT satellites before and after the 2003 collapse of the landslide, and before and after the 2007 event, have been interferometrically processed as well. Notwithstanding the restricted number of available images, the ground deformation occurred on the island due to the volcanic activity has been obtained with spatial and temporal characteristics complementary to those ones provided by GB-InSAR.

Movements of the Sciara del Fuoco

The Sciara del Fuoco (SdF) landslides that occurred at the end of December 2002 prompted researchers to install geodetic networks to monitor deformations related to potential new slope failures. With this aim, an integrated multiparametric monitoring system was designed and deployed. In particular, this complex monitoring system is composed of four single systems: an electronic distance measurement network, installed immediately after the landslide events, a real-time GPS network, a ground-based interferometric linear synthetic aperture radar (GB-InSAR), and an automated topographic monitoring system (named Theodolite Robotic Observatory of Stromboli, or THEODOROS); the three last systems provided a continuous monitoring of selected points or sectors of the SdF. Data acquired from different systems have been jointly analyzed to reach a better understanding of the SdF dynamics. Displacement data obtained from the topographic systems are compared with those obtained from GB-InSAR, and the results of the comparison are analyzed and discussed. Furthermore, in this chapter, an example of a warning system that can detect slope instability precursors on the SdF based on a statistical analysis of the data collected by the THEODOROS system is reported.