1,720,981 research outputs found
Immagini Landsat ETM+ e NDVI differencing per lo studio della deforestazione nel Mato Grosso meridionale (Brasile).
No full textMultitemporal monitoring of rock walls using topographic methodologies and persistent scatterers interferometry
No full textPurpose:
Multitemporal monitoring of rock walls is aimed at checking a study area, located in the northern area of Vecchiano municipality (Pisa, Italy) which is characterized by a morphological slope with vertical rock walls, somewhere weathered and interested by fracturing systems, prone to gravitational instability phenomena. The geological hazard of the site is conditioned also by the presence of a municipal road at slope bottom which increases the risk for pedestrians.
Methods:
The rock walls were monitored by multitemporal topographic measurements carried out by Total Station (TS) using 34 prisms permanently installed on the rock walls. Among these prisms, 4 reference prisms were installed far from the walls, in areas considered to be stable over time, while the remaining 30 were located on the rock walls, in correspondence of discontinuities and on potentially unstable blocks. All the monitored prisms and targets were georeferenced by a GNSS survey carried out in static mode on 2 reference accessible points used to roto-translate the coordinates of all the targets and prisms under observation.
These topographic measurements were coupled with a satellite radar imagery analysis carried out by utilizing Sentinel-1A and 1B data, in both ascending and descending orbit, lasting for 2 years period. The chosen methodology is the Persistent Scatterers Interferometry (PSI) which uses natural or artificial targets that are considered stable over time in terms of radiometric response. Theoretically, the PSI allows to evaluate quantitatively and qualitatively the possible variations in distance of individual features (pixels) along the Line of Sight (LOS) between the satellite sensor and the object on the ground.
Given the morphological complexity of the site with heterogeneous vegetation distribution (shrubs and small bushes with scattered grassy areas), limestone outcrops, and the poor presence of man-made structures to be considered stable over time, three metal targets were designed and subsequently installed on the edge of the rock walls. The reason of this installation was to guarantee the presence of some artificial metal targets to be used as persistent scatterers.
Results:
The TS measurements were performed every 4 months, for 2 years, with the following settings: two face measurement, for 10 repeated times at each cycle, for every prism. None of the monitored prisms have recorded significant displacements both in terms of elevation and slope distance. PSI analysis showed that the area is generally stable downstream of the monitored wall with speed along the LOS generally within the tolerances of the technique (± 2mm/year).
Conclusions:
Topographic monitoring showed that the rock walls, in the monitored time span, was stable, with no movements suggesting an imminent detachment of material. On the other hand, some anomalies in the data have brought to light how the area, where the fixed base of the TS is located, is affected by the seasonal variations of the groundwater which determine subsidence and significant oscillations of the soil level up to 6 mm. The PSI analysis allowed to assess and confirm this subsidence most probably due to the TS location on the alluvial plain
Applicazione del metodo di NDVI differencing per la valutazione della deforestazione nel Mato Grosso meridionale (Brasile).
No full textHazard Assessment of Rocky Slopes: An Integrated Photogrammetry–GIS Approach Including Fracture Density and Probability of Failure Data
Full text linkNatural rock slopes require accurate engineering–geological characterization to determine their stability conditions. Given that a natural rock mass is often characterized by a non-uniform fracture distribution, the correct, detailed, and accurate characterization of the discontinuity pattern of the
rock mass is essential. This is crucial, for example, for identifying the possibility and the probability of kinematic releases. In addition, complete stability analyses of possible rockfall events should be performed and used to create hazard maps capable of identifying the most dangerous parts of a rock
mass. This paper shows a working approach that combines traditional geological surveys and remote sensing techniques for engineering–geological investigations in a natural rock slope in Northern Italy. Discontinuities were identified and mapped in a deterministic way by using semi-automatic
procedures that were based on detailed 3D Unmanned Aerial Vehicle photogrammetric-based point cloud data and provided georeferenced representations of thousands of fractures. In this way, detailed documentation of the geo-mechanical and geo-structural characteristics of discontinuities were obtained and subsequently used to create fracture density maps. Then, traditional kinematic analyses and probabilistic stability analyses were performed using limit equilibrium methods. The results were then managed in a GIS environment to create a final hazard map that classifies different portions of the rock slope based on three factors: kinematic predisposition to rockfall (planar sliding, wedge sliding, toppling), fracture density, and probability of failure. The integration of the three hazard factors allowed the identification of the most hazardous areas through a deterministic and accurate procedure, with a high level of reliability. The adopted approach can therefore be very useful to determine the areas in which to prioritize remediation measures with the aim of reducing the level of risk
Stereofotogrammetria digitale terrestre per la valutazione della stabilità nei versanti in roccia
No full textAnalisi di stabilità di un pendio detritico montano tramite impiego di georadar installato su drone
Full text linkIl presente lavoro descrive le attività svolte in merito alla verifica della stabilità di un pendio detritico naturale posto in zona montana di difficile accesso nella catena delle Alpi Occidentali.
I dati necessari alle analisi sono stati raccolti ed elaborati attraverso tecniche geomatiche quali, in particolare, rilievi fotogrammetrici con drone con lo scopo di acquisire delle foto prospettiche dalle quali produrre una nuvola di punti georeferenziata e successivamente un ortofotomosaico. Il rilievo è stato eseguito con un drone tipo DJI Mavic 2 Pro. Contestualmente ai rilievi fotogrammetrici sono stati eseguiti rilievi topografici di Ground Control Points necessari nella fase di orientamento esterno dei fotogrammi. I fotogrammi sono stati elaborati utilizzando il software Agisoft Metashape. La nuvola 3D densa prodotta è stata successivamente interpolata in modo da generare un modello digitale denso della superficie (DDSM) in formato raster. Sulla base del DDSM sono state ortocorrette le immagini fotografiche ottenendo degli ortofotomosaici.
Allo scopo di determinare lo spessore della coltre detritica naturale al di sopra del bedrock, sono stati eseguiti 2 rilievi geofisici utilizzando lo strumento COBRA Plug‐In GPR Model SE-150, installato su drone DJI M600Pro. L’indagine si è svolta sorvolandolo direttamente l’area di interesse a circa 1.5 metri dalla superficie e raggiungendo aree altrimenti non investigabili per motivi di sicurezza. I dati del rilievo georadar sono stati elaborati con l’ausilio dell’applicativo PRISM® 2.6.
La nuvola di punti 3D ottenuta dal rilievo fotogrammetrico ha permesso la ricostruzione delle corrette geometrie del corpo detritico naturale. Tramite il software open source CloudCompare Omnia, sono stati selezionati profili rappresentativi dell’area di interesse in seguito importati all’interno del software RocScience Slide2. La ricostruzione della profondità del contatto tra la copertura detritica e il bedrock è stata eseguita estrapolando le informazioni ricavate dalle tracce georadar più prossime al profilo di interesse.
Le verifiche sono state effettuate valutando diversi scenari quali: condizioni statiche, dinamiche con presenza di sisma, condizioni statiche con presenza di neve e dinamiche con presenza contemporanea di neve e sisma.
L’impiego del georadar installato su un drone si è dimostrato un ottimo metodo di indagine in situazioni in cui l’area di studio risulta essere inaccessibile alle classiche analisi geofisiche per motivi morfologici e di sicurezza. La combinazione quindi di dati ottenuti tramite rilievi topo-cartografici e areofotogrammetrici con rilievo geofisico da drone ha permesso lo studio della stabilità di un versante naturale in area critica
Analysis of tectonic lineaments by means of high-medium resolution satellite imagery interpretation and digital photogrammetry: an application to the high speed railroad line Florence-Bologna (Northern Italy)
No full textSeasonal land subsidence and rebound monitoring in the Lucca plain (central Italy) with ERS 1&2 and in situ observations
No full textThe Corniglio landslide area (Parma, Italy): evidences for a deep seated gravitational slope deformation
No full textCluster analysis applied to engineering geological mapping
Full text linkCluster analysis of morphometric variable is reported in this paper to support characterization of rock masses and deposits. The first technique is related to fast mechanical characterization of bedrock and the second one on the mapping of the depth of superficial deposits. In order to extrapolate site-specific information to the whole study area two techniques are applied to morphometric space: supervised and unsupervised classifications through the algorithms maximum likelihood and ISODATA, respectively. The analysis of morphometric space with these techniques has provided significant results in order to discriminate bedrocks with different mechanical characteristics and the depth of superficial deposits
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