1,720,977 research outputs found
Ground motion identification, monitoring and modelling through multi-sensor A-DInSAR data
Get PDFGround motion represents the main reaction to superficial and deep deformations induced by multiple natural and anthropic phenomena which take place at different spatio-temporal scale. Recent advanced ground deformation investigations make use of satellite Synthetic-Aperture Radar (SAR) data, a new remote sensing tool, to obtain the displacement time series of measuring points over wide areas at millimiters resolution. In the last two decades, A-DInSAR techniques have experienced a major development, which is mainly related to (i) the progress of the SAR data acquired by the COSMO-SkyMed satellites and the recent ESA Sentinel missions, that act at higher spatio-temporal resolution, and to (ii) the development of advanced processing algorithms. The improvements in the A-DInSAR technique need of an appropriate methodology to analyse extremely large datasets which consist of huge amounts of measuring points with high temporal resolution. This work contributes to address to these problems by exploiting the great potential contained in the A-DInSAR time series. The project aims are:
1.Development of a methodology to analyse multi-sensor and multi-temporal A-DInSAR dataset for the geological interpretation of areas affected by ground motion;
2.Analysis of the mechanisms of ground motion mainly due to groundwater level change;
3.Integration of A-DInSAR data with numerical models.
The study has been carried out in areas representative of moderate rates of displacement (the valley bottom of the Oglio river, in Italy), of swelling-shrinkage of clayey soils (Oltrepo Pavese, in Italy), of coastal subsidence (Ravenna, in Italy), of slope instabilities (Piemonte Region, in Italy), of high rate of pumping-induced subsidence (Alto Guadalentín Basin, in Spain) and of ground motion due to groundwater level change (London Basin, in United Kingdom). In the investigation site of the Oltrepo Pavese, the developed methodology allowed the disentanglement of natural and man-induced processes through the analyses of ERS-1/2 and RADARSAT data. The results were useful to gain insight into three deformational behaviours: linear, non-linear, and seasonal components of motion. In the valley bottom of the Oglio river, a Pre-Alpine valley located upstream the Iseo Lake, the application of the methodology, through ERS-1/2 and RADARDAT data, highlighted the geomorphologic control of the subsidence pattern. Multiple datasets have been employed for the Ravenna case-study such as: ERS-1/2, Envisat, TerraSAR-X and Sentinel-1 to test the capability to recognize ground motion areas. The reproducibility of the methodology was also assessed for landslides investigation in the Piemonte Region.
The analysis of the mechanisms, mainly due to groundwater level change, was performed in the Alto Guadalentín Basin in Spain. In this basin, the land subsidence due to the groundwater overexploitation reaches the higher values measured of Europa (>10 cm/yr). The approach allowed to understand that very thick soft soil layer with low permeability that has been drained since the 1960s, are involved in slow consolidation process, where the maximum settlement has yet to be reached.
Finally, London Basin was chosen to model ground motion due to groundwater level change; by applying 1D model, since the large availability of geological, hydrogeological and geotechnical data. In this case the integration of A-DInSAR data in the modelling permitted to analyse the spatio-temporal variability of the ground motion response to groundwater levels variations across the London Basin.
Overall, the study demonstrates how a better knowledge of ground deformations and the occurrence, measurement, mechanics and prediction can be reached by combining A-DInSAR with geological, geotechnical and hydrogeological data. The results could be used for land use planning and civil protection purposes, providing fundamental information to adopt appropriate mitigation measures
Satellite based radar interferometry to mapping and monitoring swelling/shrinking clay soils
No full textA methodology for the study of swelling/shrinkage through the satellite radar images acquired from 1992 to 2010 by different sensors (ERS, RADARSAT) and processed by means of the SqueeSARTM technique is proposed. The methodology aimed at improving the understanding of the kinematical behavior of swelling/shrinking processes, mapping these soils, monitoring the soil volume change and enabling also non-expert users to handle DInSAR data. The methodology has been applied and validated in an area of the Northern Italy where swelling/shrinking soils are frequent. The map of the ground displacements was compared with the geological model of the subsurface and with the distribution of the damaged buildings. The obtained results are helpful in land use planning to identify and quantify the swelling/ shrinkage of clay soils
Methodology for Detection and Interpretation of Ground Motion Areas with the A-DInSAR Time Series Analysis
Get PDFRecent improvement to Advanced Differential Interferometric SAR (A-DInSAR) time series quality enhances the knowledge of various geohazards. Ground motion studies need an appropriate methodology to exploit the great potential contained in the A-DInSAR time series. Here, we propose a methodology to analyze multi-sensors and multi-temporal A-DInSAR data for the geological interpretation of areas affected by land subsidence/uplift and seasonal movements. The methodology was applied in the plain area of the Oltrepo Pavese (Po Plain, Italy) using ERS-1/2 and Radarsat data, processed using the SqueeSAR™ algorithm, and covering time spans, respectively, from 1992 to 2000 and from 2003 to 2010. The test area is a representative site of the Po Plain, affected by various geohazards and characterized by moderate rates of motion, ranging from −10 to 4 mm/yr. Different components of motion were recognized: linear, non-linear, and seasonal deformational behaviors. Natural and man-induced processes were identified such as swelling/shrinkage of clayey soils, land subsidence due to load of new buildings, moderate tectonic uplift, and seasonal ground motion due to seasonal groundwater level variations
Characterisation of hydraulic head changes and aquifer properties in the London Basin using Persistent Scatterer Interferometry ground motion data
Get PDFIn this paper, Persistent Scatterer Interferometry was applied to ERS-1/2 and ENVISAT satellite data covering 1992–2000 and 2002–2010 respectively, to analyse the relationship between ground motion and hydraulic head changes in the London Basin, United Kingdom. The integration of observed groundwater levels provided by the Environment Agency and satellite-derived displacement time series allowed the estimation of the spatio-temporal variations of the Chalk aquifer storage coefficient and compressibility over an area of ∼1360 km2. The average storage coefficient of the aquifer reaches values of 1 × 10−3 and the estimated average aquifer compressibility is 7.7 × 10−10 Pa−1 and 1.2 × 10−9 Pa−1 for the periods 1992–2000 and 2002–2010, respectively. Derived storage coefficient values appear to be correlated with the hydrogeological setting, where confined by the London Clay the storage coefficient is typically an order of magnitude lower than where the chalk is overlain by the Lambeth Group. PSI-derived storage coefficient estimates agree with the values obtained from pumping tests in the same area. A simplified one-dimensional model is applied to simulate the ground motion response to hydraulic heads changes at nine piezometers. The comparison between simulated and satellite-observed ground motion changes reveals good agreement, with errors ranging between 1.4 and 6.9 mm, and being 3.2 mm on average
PSI-based methodology to land subsidence mechanism recognition
Get PDFA methodology based on Persistent Scatterer Interferometry (PSI) is proposed
in order to disentangle the contribution of different processes that act at
different spatio-temporal scales in land subsidence (i.e. vadose zone
processes as swelling/shrinkage of clay soils, soil consolidation and fluid
extraction). The methodology was applied in different Italian geological
contexts characterized by natural and anthropic processes (i.e. a Prealpine
valley and the Po Plain in northern Italy)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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