Landslide Ground Based Remote Sensing Monitoring: Formigal Case Study (Huesca, Spain)

Galahad is an ongoing Specific Targeted Research Project developed within the EU 6th Framework Programme ¿ Priority 1.1.6.3. The objective is to retrieve, through the use of improved GB-SAR and TLS technologies, field parameters that can be used in prediction algorithms of landslides, avalanches and glaciers related hazards. The landslide study area is located in the ski resort of Formigal, central Pyrenees (province of Huesca, Spain). The excavation of a parking area in the summer of 2004 reactivated a complex paleolandslide creating new sliding surfaces. The movement extends over an area of 0.25 km2 and experienced displacements as large as 0.5 cm/day during the period 2004¿2005. Stabilization engineering solutions were carried out reducing maximum observed displacement to 0.2 cm/day at the end of 2005. Within Galahad performed activities consisted in the collection of data on the landslide useful for its detailed characterization and the execution of a series of site measurement campaigns with GB-SAR, TLS and Differential GPS (D-GPS). The monitoring activities started in May 2006 completing a series of four campaigns with Total Station and D-GPS, a continuous two month data acquisition with GB-SAR and several TLS scans during two different periods from three points of view over the landslide. In this paper data obtained by GB-SAR and TLS are compared with D-GPS data, and a good agreement has been found between data sets. The project is still in progress and new site measurement campaigns with GB-SAR, TLS and D-GPS in 2007 will provide further insight into landslide forecasting models.JRC.H.7-Land management and natural hazard

Universal fluctuations in tropospheric radar measurements

Radar data collected at an experimental facility arranged on purpose suggest that the footprint of atmospheric turbulence might be encoded in the radar signal statistics. Radar data probability distributions are calculated and nicely fitted by a one-parameter family of generalized Gumbel (GG) distributions, Ga. A relation between the wind strength and the measured shape parameter a is obtained. Strong wind fluctuations return pronounced asymmetric leptokurtic profiles, while Gaussian profiles are eventually recovered as the wind fluctuations decrease. Besides stressing the crucial impact of air turbulence for radar applications, we also confirm the adequacy of Ga statistics for highly correlated complex systems

Ground Based SAR and Terrestrial Laser Scanner Data for the Analysis of the Formigal Landslide; the GALAHAD Project Test Site in the Spanish Pyrenees

An old, dormant landslide in the ski resort of Formigal at Sallent de Gállego (Huesca), Central Pyrenees, Spain, was partly reactivated in 2004 as a result of excavation works at its toe for the construction of a car park, thus endangering the car park and a newly built section of the road to El Portalet mountain pass, at the French border. Bedrock in the landslide area consists predominantly of weathered shales/slates and sandstones with some occurrences of limestone layers, all of Devonian to Carboniferous age, overlaid by colluvial deposits containing some calcareous boulders in a sandy clay matrix. The reactivated landslide sector has an extent of 0.25 km2; it shows small hummocks and ponds, and it is mainly covered with grass vegetation, with calcareous boulders locally outcropping. This landslide is being monitored as part of the EU 6th Framework Programme¿s GALAHAD Project. Soon after the landslide reactivation, a first monitoring campaign was carried out including the installation of inclinometers and extensometers and the use of GPS and Total Station, in addition to the geomechanical characterization of the landslide materials (Aramón, 2005). Inclinometer readings indicated the presence of a roto-traslational failure surface at a depth of 7 to 16 m. This campaign was followed by the implementation of stabilization measures at the toe of the reactivated landslide sector, which considerably slowed down the landslide movement. Later on, in the framework of the GALAHAD Project, surface displacement monitoring was performed during 2006 using mainly state-of-the-art terrestrial remote sensing systems. These included a C-band, VV polarization, 2 m linear scan length, ground-based interferometric SAR (GB-SAR) (Luzi et al., 2006) providing hourly interferograms for mapping displacements over a 53-day period, and a long-range Optech Ilris 3-D terrestrial laser scanner (TLS), acquiring multi-temporal, 3-D dense point cloud coordinates in two surveys from two different viewpoints, three months apart (see e.g. Abellán, et al., 2006). Simultaneously to these measurements and extending over a longer period of time, RTK-based differential GPS (D-GPS) monitoring was carried out using a Leica System 1200, collecting multi-temporal XYZ coordinates over 97 stations both for determining displacement rates and for georeferencing the GB-SAR and TLS data. The maximum accumulated modulus of displacement measured by D-GPS amounted to 22.6 cm over a 6-month period embracing the shorter GB-SAR and TLS monitoring campaigns, with displacement velocities changing with time. Displacements shown on the GB-SAR multi-temporal differential interferograms, including also those for corner and active SAR signal reflectors precisely located at a number of GPS stations, showed a good agreement with those obtained by D-GPS over the common 53-day measurement period, with an average difference of ± 1.68 cm and a standard deviation of ± 1.51 cm for average maximum displacements of about 8 cm. Processing of the TLS-acquired data is still in progress. Preliminary meteorological analysis appeared to show generally a good correlation between the landslide higher velocity periods and intense rainfall events. Further analysis, also investigating the possible correlation with snow melting, is envisaged to be performed once the TLS-based movement measurements are available. The results of the analysis are intended to be used for building a landslide forecasting model.JRC.H.7-Land management and natural hazard

Quality assurance multicenter comparison of different MR scanners for quantitative diffusion-weighted imaging

To propose a magnetic resonance imaging (MRI) quality assurance procedure that can be used for multicenter comparison of different MR scanners for quantitative diffusion-weighted imaging (DWI)