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Applications of multi-temporal terrestrial laser scanner measurements to monitor the evolution of unstable slopes and glaciers

pubblicazioni - Articolo

Applications of multi-temporal terrestrial laser scanner measurements to monitor the evolution of unstable slopes and glaciers

measurements to monitor the evolution of unstable slopes and glaciers Paolo Federici*, Andrea Tamburini**, Davide Martelli**, Oriol Monserrat*** Gerardo Herrera****, Linhsia Noferini*****, Helmut Rott ****** International Disaster and Risk Conference – IDRC 2008 Davos, Switzerland, 25-29 Agosto 2008 POSTER SESSION * CESI RICERCA ** IMAGEO, TORINO *** IG, BARCELONA **** IGME, MADRID ***** UNIVERSITÀ DI FIRENZE ****** ENVEO Laser scanning is a relatively new surveying technique, which allows obtaining a so-called point cloud set of data, represented in a user defined 3D reference system. The long-range Terrestrial Laser Scanner (TLS) is a laser based digitizing system that provides very detailed 3D models at a maximum instrumental range of 1 – 1.5 km. The point cloud of the scanned surface is generally obtained by aligning partially overlapped individual scans each one covering a part of the scanned scene. Measuring displacements of unstable slopes and glaciers by means of conventional techniques may be difficult. The access to the unstable areas is needed for the most part of conventional surveying techniques and may be dangerous, even impossible, during emergency situations. Recently developed monitoring techniques (TLS, Ground-Based-SAR) give the possibility to monitor unstable areas without accessing them and verify the reliability of punctual displacements obtained from independent periodical measurements (GPS or topographic traditional). The extraction of the surface movements from multi-temporal point clouds of an unstable area using TLS technique is based on the calculation of a roto-translation matrix, obtained from the alignment of multi-temporal scans and the computation of x, y, z components of the mean displacement vector. A proper workflow for retrieving surface displacements of landslides and glaciers by comparing multi-temporal TLS surveys was developed by the authors, in the frame of the on-going research project GALAHAD “Advanced Remote Monitoring Techniques for Glaciers, Avalanches and Landslides Hazard Mitigation” (EU FP6, Contract N. 018409) – www.galahad.eu. The proposed methodology is described in the paper. Three different applications are presented: a rotational landslide affecting the internal side of a morainic ridge (Locce Glacier, Macugnaga, M. Rosa, Italy), the complex landslide of Formigal test site (Huesca, Spain), affected by decimetric yearly displacement rate and the debris covered Belvedere Glacier (Macugnaga, M. Rosa, Italy) surveyed during summer 2007. Both the Formigal landslide and the Belvedere Glacier have been selected as test sites within GALAHAD. Finally, considerations are developed, relevant to the integration of TLS with other innovative remote monitoring techniques, like GB-SAR (also developed under GALAHAD), to the reliability, precision and operative usefulness of TLS measurements and to their validation by

comparison with more conventional instruments (DGPS and Total Stations). Moreover, requirements for the use of TLS in automatic mode will be discussed through the analysis of field tests. The new features of TLS and their applications are susceptible to greatly improve the interpretation of the evolution of the landslides and glaciers and therefore the forecasting capacity and the effectiveness of mitigation interventions.

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