Riccardo Fanti

Landslide monitoring by using ground-based SAR interferometry: an example of application to the Tessina landslide in Italy

Abstract An innovative technique, based on radar interferometry and implemented using ground-based instrumentation, has been applied for monitoring the Tessina landslide (Italy, Belluno). The technique has allowed us to derive multitemporal surface deformation maps of the entire depletion zone of the landslide with a high spatial resolution and accuracy. The portable device used in this application is known as Linear SAR (LISA), and it is able to provide measurements at 17 GHz with a synthetic aperture of up to 2.8 m. The results have been validated by comparing the recorded pixel displacements with independent measurements carried out by a motorized theodolite and Electronic Distance Meter (EDM) on two benchmarks.

Rainfall thresholds for the forecasting of landslide occurrence at regional scale

This paper concerns a regional scale warning system for landslides that relies on a decisional algorithm based on the comparison between rainfall recordings and statistically defined thresholds. The latter were based on the total amount of rainfall, which was cumulated considering different time intervals: 1-, 2- and 3-day cumulates took into account the critical rainfall influencing shallow movements, whilst a variable time interval cumulate (up to 240 days) was used to consider the triggering of deep-seated landslides in low permeability terrains. A prototypal version of the model was initially set up to define statistical thresholds. Then, thresholds were calibrated using a database of past georegistered and dated landslides. A validation procedure showed that the calibration highly improves the results and therefore the model was integrated in the regional warning system of Emilia Romagna (Italy) for civil protection purposes. The proposed methodology could be easily implemented in other similar regions and countries where a sufficiently organised meteorological network is present.

Satellite radar interferometry for monitoring and early-stage warning of structural instability in archaeological sites

Satellite interferometric synthetic aperture radar (InSAR) monitoring campaigns were performed on the archaeological heritage of the Roman Forum, Palatino and Oppio Hills in the centre of Rome, Italy, to test the capabilities of persistent scatterer interferometry techniques for the preventive diagnosis of deformation threatening the structural stability of archaeological monuments and buried structures. ERS-1/2 and RADARSAT-1/2 SAR images were processed with the permanent scatterers InSAR (PSInSAR) and SqueeSAR approaches, and the identified measurement points (MP) were radar-interpreted to map the conservation criticalities in relation to the local geohazard factors and active deterioration processes. The multi-temporal reconstruction of past/recent instability events based on the MP deformation time series provided evidences of stabilization for the Domus Tiberiana as a consequence of recent restoration works, as well as of persistent deformation for the Temple of Magna Mater on the Palatino Hill and the structures of the Baths of Trajan on the Oppio Hill. Detailed time series analysis was also exploited to back monitor and understand the nature of the 2010 collapse that occurred close to Neros Golden House, and to establish an early-stage warning procedure useful to preventively detect potential instability.

Terrestrial laser scanning for rockfall stability analysis in the cultural heritage site of Pitigliano (Italy)

Traditional surveying methods are often not sufficient to achieve a complete geomechanical characterization of the rock mass, to analyze the instability mechanisms threatening the cultural heritage of hilltop historic towns. In Pitigliano (Tuscany, Central Italy), terrestrial laser scanning was employed complementarily to conventional geomechanical techniques. The overall 3D survey of the exposed surfaces was combined with scanlines of the inner walls of the subterranean cavities running underneath the historic centre. The rock mass discontinuities geometry was extracted, and the most critical instability mechanisms were mapped, with particular interest in the potential impacts on the ancient buildings located along the cliff edge. The geomechanical analysis of the surveyed joint sets confirmed a structural control on the cliff morphology by two main joint sets. Thanks to the laser scanner-based kinematic analysis, flexural toppling and wedge failure were found as the main hazardous instability mechanisms in Pitigliano. Finally, the conservation criticalities were identified and a pilot monitoring system was installed in a sector highly susceptible to block detachment.

Updating and tuning a regional-scale landslide early warning system

This work presents the last improvements of an operative regional-scale warning system developed for the management of the risk related to rainfall-induced landslides (both shallow and deep seated). The warning system is named Sistema Integrato Gestione Monitoraggio Allerta, and it is based on a set of spatially variable statistical rainfall thresholds (Martelloni et al. Landslides 9(4): 485–495, 2012b). The performance of the warning system was enhanced using a larger landslide dataset for the calibration of thresholds and readjusting the boundaries of the territorial units (TUs, the basic spatial unit of application of the warning system). Our tuning leads to define a larger number of TUs and to change some of the previous reference rain gauges. In particular, a statistical analysis highlighted that the spatial organization of missed and correctly predicted landslides does not depend on lithology, land use, and morphometric attributes; therefore, the redefinition of TUs was based on the administrative borders between municipalities. This allowed combining the TU outputs into a decisional procedure which, in a completely automated way, is able to forecast the warning levels based on objective and quantitative criteria (the number of expected landslides), in full accordance with the regional civil protection guidelines. The implementation of these updates was straightforward and could be conveniently applied to similar warning systems based on rainfall thresholds.

Hydrogeological hazard and risk in archaeological sites: some case studies in Italy

This paper describes the research activity carried out in some sample areas in Italy (Latium and Sardinia) dealing with the evaluation of geomorphologic hazard and risk with regard to landslides, floods and erosion processes for the historical sites. First of all, it is necessary to create a database of the archaeological wealth and an analysis of the geomorphologic processes interacting on them. This activity employs the Arc:Info (© ESRI Inc.) software in which the database is included for organising and georeferring all the information obtained with the direct survey analysis. All the geomorphologic processes influencing the archaeological sites (both on slopes and flood plain) were analysed to highlight the temporal and spatial distribution of elements that are threatened. The use of Geographic Information Systems provides the most effective procedure for a global and integrated analysis on the site information and on the intrinsic and external conditions of potential instability. Afterwards, the cases of hydrogeologic hazard are investigated applying geological engineering methods in order to indicate the main causes of instability and the possible remedial measures.

Geomorphology of the Rotolon landslide (Veneto Region, Italy)

In this paper a geomorphological map of the Rotolon landslide is presented. This cartographic product was obtained using a combination of accurate field surveys together with airborne Lidar analysis, aerial photo interpretation and thermographic field surveys within a GIS. The map was prepared in order to analyze the morphological features of the landslide and therefore improve interpretation of the GB-InSAR data. This monitoring device was installed on the site after the detachment of a debris mass of 225,000 m3 on 4 November 2010. The main purpose of the post-event activities, including the geomorphological characterization, was to detect the processes acting on the landslide, evaluate the hazard related to each phenomenon, understand the landslide kinematics and define the residual risk for the area. The geomorphological map suggests that debris production and detachment are hazardous phenomena that involve the surficial detrital cover of a bigger and more complex landslide. The latter has the typical characteristics of a deep-seated gravitational slope deformation. The distinction between secondary processes, which appear to be the most hazardous in the short-term, and deep seated ones, demonstrates that accurate mapping provides important information for local administrations and decision makers, allowing them to prepare landslide susceptibility and hazard models.

Early Warning GBInSAR-Based Method for Monitoring Volterra (Tuscany, Italy) City Walls

Ground-based synthetic aperture radar interferometry (GBInSAR) remote sensing technique has been repeatedly proved an effective tool for monitoring built environment affected by structural and geological criticalities. In this paper, it is described how this technique can be successfully applied for early-warning procedures and detection of ongoing deterioration processes on archeological and cultural heritage sites. An integrated approach of GBInSAR and terrestrial laser scanner (TLS) technologies was performed on Volterra test site (Tuscany, Italy), where a sudden collapse of a 35-m wide section of city walls occurred on January 31, 2014. The installed early-warning monitoring system is capable of an accurate and focused real-time displacement detection of the south-western side of the city including walls, buildings, and monuments, thus allowing prompt interventions for citizens safety and conservation purposes. The effectiveness of this alert technique became evident when the precursors of a second impressive wall collapse were clearly detected. From the beginning of the GBInSAR monitoring, we measured a constant displacement velocity of 0.1 mm/h in correspondence to a 15-m high wall sustaining the Acropolis and lying an underground parking. After a sudden increase of velocity values up to 1.7 mm/h, the local authorities were alerted so that they had time to interdict the area to citizens and to take adequate safety countermeasures two days before the collapse.

Cultural Heritage and Landslides: Research for Risk Prevention and Conservation

The impact of natural hazards on our cultural heritage represents an important theme, involving a multi-disciplinary approach. In case of landsliding, engineering geologists can play a key role, through the identification of relationships between soil and structures. This chapter starts from the large perspective of UNESCO Convention (1972), as a bird’s-eye view of the general problem of heritage conservation, arriving at the presentation of a series of case histories from different countries. This varied approaches to the problem of landslides and cultural heritage reflects the multitudes of interests associated with this topics.

Testing cost-effective methodologies for flood and seismic vulnerability assessment in communities of developing countries (Dajç, northern Albania)

Nowadays many developing countries need effective measures to reduce the disaster related risks. Structural interventions are the most effective to achieve these aims. Nevertheless, in the absence of adequate financial resources different low-cost strategies can be used to minimize losses. The purpose of this paper is to demonstrate that the disaster risk reduction can be gathered building a community coping capacity. In the case study, flood and seismic analyses have been carried out using relatively simple and low-cost technologies, fundamental for governments and research institutions of poorly developed countries. In fact, through the acquisition and dissemination of these basic information, a reduction of vulnerability and risk can be achieved. In detail, two methodologies for the evaluation of hydraulic and seismic vulnerability were tested in the Dajç municipality (Northern Albania), a high-seismicity region that is also severely affected by floods. Updated bathymetric, topographic and hydraulic data were processed with HEC-RAS software to identify sites potentially affected by dykes overflowing. Besides, the soil-structure interaction effects for three strategic buildings were studied using microtremors and the Horizontal to Vertical Spectral Ratio method. This flood and seismic vulnerability analysis was then evaluated in terms of costs and ease of accessibility in order to suggest the best use both of the employed devices and the obtained information for designing good civil protection plans and to inform the population about the right behaviour in case of threat.