Sandro Silvano

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.

A critical review of landslide monitoring experiences

Over the past few years, the monitoring of natural phenomena has acquired great importance for the scientific community. It aims to understand the mechanisms of disruptive processes, define adequate prevention measures for the mitigation of their effects and reduce the loss of human lives and assets. In order to detect the stability conditions of slopes belonging to different geological and environmental contexts, geotechnical investigations have been carried out since 1982. The various types of landslides to be investigated, and the diverse socio-economic contexts involved, have shown the need for constant surveillance, using the most up-to-date technology available. For this purpose, automatic recording systems connected to different sensors have been installed, (and also serve civil defence purposes). During this research activity, several problems arose, and several solutions had to be found. In this paper, some of the main problems concerning the installation and management of monitoring equipment used for the study of three landslides will be discussed.

Monitoring landslides from optical remotely sensed imagery: the case history of Tessina landslide, Italy

Collecting information on landslide occurrence and activity over wide areas is a crucial task for landslide hazard assessment. Field techniques, despite being very precise, are usually not sufficient to achieve this goal, since they mostly provide pointbased measurements. Mainly because of its synoptic view and its capability for repetitive observations, optical (visible-infrared) remotely sensed imagery acquired at different dates and at high spatial resolution can be considered as an effective complementary tool for field techniques to derive such information. An image-processing method to map and monitor landslide activity using multitemporal optical imagery is proposed. The method entails automatic change detection of suitably pre-processed (geometrically registered and radiometrically normalised) sequential images, followed by thresholding into landslide-related change pixels. Subsequent filtering based on the degree of rectangularity of regions can also be considered to eliminate pixel clusters corresponding to man-made land use changes. The application of this method is illustrated in the complex Tessina landslide in the Eastern Italian Alps. It has focused on discriminating the effects of a major reactivation that occurred in 1992, hence inferring the dynamics of the landslide at that time. Although the method has been devised for optical remote sensing imagery in general, in the absence of high-resolution satellite imagery covering that period, digital images derived by scanning existing aerial photograph diapositives at 1-m pixel size have been used. The method is able to classify image pixels according to landslide activity conditions. D 2003 Elsevier Science B.V. All rights reserved.

A visco-plastic model for slope analysis applied to a mudslide in Cortina d'Ampezzo, Italy

Abstract This paper describes a visco-plastic model which, using recorded groundwater levels, is capable of simulating the velocity trend in landslides. It also deals with the phenomenon of shear strength regain that occurs in montmorillonitic clays constituting slopes during periods when landslides are stationary. The model has been validated with long-term observations of a clay slope affected by a mudslide.

Simulation of the 1992 Tessina landslide by a cellular automata model and future hazard scenarios

Abstract Cellular Automata are a powerful tool for modelling natural and artificial systems, which can be described in terms of local interactions of their constituent parts. Some types of landslides, such as debris/mud flows, match these requirements. The 1992 Tessina landslide has characteristics (slow mud flows) which make it appropriate for modelling by means of Cellular Automata, except for the initial phase of detachment, which is caused by a rotational movement that has no effect on the mud flow path. This paper presents the Cellular Automata approach for modelling slow mud/debris flows, the results of simulation of the 1992 Tessina landslide and future hazard scenarios based on the volumes of masses that could be mobilised in the future. They were obtained by adapting the Cellular Automata Model called SCIDDICA, which has been validated for very fast landslides. SCIDDICA was applied by modifying the general model to the peculiarities of the Tessina landslide. The simulations obtained by this initial model were satisfactory for forecasting the surface covered by mud. Calibration of the model, which was obtained from simulation of the 1992 event, was used for forecasting flow expansion during possible future reactivation. For this purpose two simulations concerning the collapse of about 1 million m 3 of material were tested. In one of these, the presence of a containment wall built in 1992 for the protection of the Tarcogna hamlet was inserted. The results obtained identified the conditions of high risk affecting the villages of Funes and Lamosano and show that this Cellular Automata approach can have a wide range of applications for different types of mud/debris flows.

Collecting data to define future hazard scenarios of the Tessina landslide

Abstract Research has been carried out within the framework of the RUNOUT project to define future hazard scenarios of the Tessina Landslide and to determine whether the slide can be related to hydrogeological factors or deep tectonic structures/discontinuities. The work consisted mainly of mapping the geology and geomorphology, collecting meteorological, hydrological and kinematic data, and data modelling. We describe the monitoring system installed on the Tessina landslide and the analyses of data acquired since the start of RUNOUT, a project funded by the EC. Our main goal was to support the group doing the modelling by providing measurements of the principal parameters, such as displacements, groundwater level variations, rainfall, etc., for improving the models used to simulate the behaviour of the landslide and forecast the risk scenarios for the villages. We discuss the critical phase of September-October 1998 and propose a possible future geomorphological evolution of the landslide based on analysis of this data. The second goal was to focus the monitoring on maintaining an alarm system for the safety of the population threatened by the landslide.

Ground-based monitoring of high-risk landslides through joint use of laser scanner and interferometric radar

Terrestrial laser scanner (TLS) and interferometric synthetic aperture radar (InSAR) allow the acquisition of data on an observed surface with high spatial sampling rate. The data provided by TLS observation of a landslide ground surface can be used to generate a very detailed digital model of this surface, and multitemporal observations with TLS or continuous or multitemporal observation with InSAR can provide a reliable displacement map. In order to acquire useful information about the analogies, differences, and capabilities, as well as limitations of these techniques, a joint experimentation of TLS and InSAR was performed over two years in various sites in the Italian Alps. The results have indicated that these techniques can provide high‐quality data, can be very useful in the monitoring intended for the mitigation of hydrogeological risk in a wide range of cases, and must be supported by a topographical georeferenced network.