Cristina Castagnetti

Multi-sensors integrated system for landslide monitoring: critical issues in system setup and data management

Abstract This paper discusses critical issues related to the reliability of topographic monitoring systems such as ATS (Automated Total Stations), GNSS (Global Navigation Satellite System) and Ground Based InSAR focusing the attention on controlling the stability of networks infrastructure, which have influence on data correction procedures but are often taken for granted, and on integrating results in GIS (Geographic Information System), under a common reference framework and with respect to open-access ancillary data. The novelty of the paper lies in the demonstration of the efficiency obtained by a proper implementation of the system. Discussion makes reference to an active landslide by using ATS, GNSS and Ground Based InSAR in continuous and periodic mode.

Recent approaches in geodesy and geomatics for structures monitoring

AbstractMonitoring the time history of structures and infrastructures has always been an important area of application of geodetic and geomatic methods. Here we shall concentrate on the item of monitoring ancient buildings because, beyond its intrinsic interest, it provides a good illustration of some of the most recent monitoring techniques. Identifying the overhang, progressive changes of inclination, differential movements of the structure and detailing the study of structural elements are just some examples of the many fundamental and necessary information for structural engineers. Those data are required to study and analyze the behavior of a structure with the purpose to assess the stability. Looking at the several methods offered by Geomatics, laser scanning appears to be the best technology to provide an effective 3D solution to those requirements. Surveying by means of a terrestrial laser scanner, allows to detect a huge number of 3D information with high accuracy in a relatively short time and high accuracy. Just analyzing the point clouds, interesting information along with useful products can be obtained in order to draw some considerations about the investigated structure. This research aims at suggesting a new philosophy for using 3D models in a diagnostic perspective in order to study structures along with their actual dimensions, their stability and so on. Traditionally, indeed, laser scanning is chosen for artistic and architectural studies and the resulting three-dimensional model represents what often is of concern. Furthermore, the use of more classic techniques, such as total station and digital leveling, and LST is fundamental as an integrated approach for the monitoring of ancient buildings. The integration of different techniques allow a redundancy of observation and the possibility to verify the results obtained form independent techniques as is shown throughout some experimental applications.

A reliable methodology for monitoring unstable slopes: the multi-platform and multi-sensor approach

High resolution topography, by involving Digital Terrain Models (DTMs) and further accurate techniques for a proper displacement identification, is a valuable tool for a good and reliable description of unstable slopes. By comparing multitemporal surveys, the geomorphology of a landslide may be analyzed as well as the changes over time, the volumes transportation and the boundaries evolution. Being aware that a single technique is not sufficient to perform a reliable and accurate survey, this paper discusses the use of multi-platform, multi-source and multi-scale observations (both in terms of spatial scale and time scale) for the study and monitoring of unstable slopes. The final purpose is to highlight and validate a methodology based on multiple sensors and data integration, useful to obtain a comprehensive GIS (Geographic Information System) which can successfully be used to manage natural disasters or to improve the knowledge of a specific phenomenon in order to prevent and mitigate the hydro-geological risk. The novelty of the present research lies in the spatial integration of multiple remote sensing techniques such as: integration of Airborne Laser Scanning (ALS) and Terrestrial Laser Scanning (TLS) to provide a comprehensive and accurate surface description (DTM) at a fixed epoch (spatial continuity); continuous monitoring by means of spatial integration of Automated Total Station (ATS) and GNSS (Global Navigation Satellite System) to provide accurate surface displacement identification (time continuity). Discussion makes reference to a rockslide located in the northern Apennines of Italy from 2010 to 2013.

Large-Scale Slope Instability Affecting SS63 Near the Cerreto Pass (Northern Apennines, Italy)

National Road SS63 is endangered by large scale slope instability phenomena few km north of the Cerreto Pass (northern Apennines, Italy). At the Col Piagneto slope, SS63 was closed two times in the past 50 years after landslide events. In 1974, the collapse of portion of a rock slide triggered a debris slide that buried more than 50 m of the road track. In 2008, the reactivation of an earth slide in eastern portion of the slope damaged about 400 m of the “new” track built to by-pass the 1974 risk area. In order to evaluate if it is worthwhile keeping the old track open to traffic, or it is maybe better to repair the new track a comprehensive study was financed by Emilia Romagna Region. Research methods included: high resolution DEM, landslides mapping, continuous displacement and groundwater monitoring. Results allowed to assess different semi-quantitative risk scenario for the road structures or vehicles.

An Integrated Procedure to Assess the Stability of Coastal Rocky Cliffs: From UAV Close-Range Photogrammetry to Geomechanical Finite Element Modeling

The present paper explores the combination of unmanned aerial vehicle (UAV) photogrammetry and three-dimensional geomechanical modeling in the investigation of instability processes of long sectors of coastal rocky cliffs. The need of a reliable and detailed reconstruction of the geometry of the cliff surfaces, beside the geomechanical characterization of the rock materials, could represent a very challenging requirement for sub-vertical coastal cliffs overlooking the sea. Very often, no information could be acquired by alternative surveying methodologies, due to the absence of vantage points, and the fieldwork could pose a risk for personnel. The case study is represented by a 600 m long sea cliff located at Sant’Andrea (Melendugno, Apulia, Italy). The cliff is characterized by a very complex geometrical setting, with a suggestive alternation of 10 to 20 m high vertical walls, with frequent caves, arches and rock-stacks. Initially, the rocky cliff surface was reconstructed at very fine spatial resolution from the combination of nadir and oblique images acquired by unmanned aerial vehicles. Successively, a limited area has been selected for further investigation. In particular, data refinement/decimation procedure has been assessed to find a convenient three-dimensional model to be used in the finite element geomechanical modeling without loss of information on the surface complexity. Finally, to test integrated procedure, the potential modes of failure of such sector of the investigated cliff were achieved. Results indicate that the most likely failure mechanism along the sea cliff examined is represented by the possible propagation of shear fractures or tensile failures along concave cliff portions or over-hanging due to previous collapses or erosion of the underlying rock volumes. The proposed approach to the investigation of coastal cliff stability has proven to be a possible and flexible tool in the rapid and highly-automated investigation of hazards to slope failure in coastal areas.

Remotely Piloted Aircraft Systems (RPAS) for high resolution topography and monitoring: civil protection purposes on hydrogeological contexts

The proposed work concerns the analysis of Remotely Piloted Aircraft Systems (RPAS), also known as drones, UAV (Unmanned Aerial Vehicle) or UAS (Unmanned Aerial System), on hydrogeological contexts for civil protection purposes, underlying the advantages of using a flexible and relatively low cost system. The capabilities of photogrammetric RPAS multi-sensors platform were examined in term of mapping, creation of orthophotos, 3D models generation, data integration into a 3D GIS (Geographic Information System) and validation through independent techniques such as GNSS (Global Navigation Satellite System). The RPAS used (multirotor OktoXL, of the Mikrokopter) was equipped with a GPS (Global Positioning System) receiver, digital cameras for photos and videos, an inertial navigation system, a radio device for communication and telemetry, etc. This innovative way of viewing and understanding the environment showed huge potentialities for the study of the territory, and due to its characteristics could be well integrated with aircraft surveys. However, such characteristics seem to give priority to local applications for rigorous and accurate analysis, while it remains a means of expeditious investigation for more extended areas. According to civil protection purposes, the experimentation was carried out by simulating operational protocols, for example for inspection, surveillance, monitoring, land mapping, georeferencing methods (with or without Ground Control Points - GCP) based on high resolution topography (2D and 3D information).

Contribution of Geomatics Engineering and VGI Within the Landslide Risk Assessment Procedures

This paper presents a literature review on the methodology called Volunteered Geographic Information (VGI) and its use for Landslide Risk Assessment (LRA). General risk assessment procedures are discussed and the potential contributions of VGI are identified, in particular when quantitative characterization of factors such as Hazard, Vulnerability and Exposure is required. The review shows that the standard LRA procedures may benefit from input given by surveyors when performing hazard assessments, while crowdsourced data would be a valuable support in vulnerability/damage assessment studies. The review also highlights several limitations related to the role of VGI and crowdsourcing in LRA.