1,720,983 research outputs found
Ground Dynamics in the Norwegian Periglacial Environment Investigated by Synthetic Aperture Radar Interferometry
Full text linkCold polar and mountainous periglacial environments are characterised by highly dynamic ground surfaces that move under the action of frost and gravity, and contribute to shaping the landscape. The movement rates and directions are spatially and temporally variable, depending on the involved periglacial processes and their environmental controlling factors. Spaceborne Synthetic Aperture Radar (SAR) has revolutionised the investigation of the ground surface in polar and mountainous regions, due to its ability to image large and remote areas independently of light and meteorological conditions. By comparing images taken at different times, the SAR Interferometry (InSAR) technique can remotely detect ground surface displacements at centimetre to millimetre accuracy.
This thesis exploits the InSAR technology to analyse the spatial distribution and temporal variability of the ground surface displacements in periglacial environments. The spatio-temporal displacement patterns are documented on a regional scale, allowing for the study of the kinematic signatures of various frost- and gravity-driven processes. The research takes advantage of the Copernicus Sentinel-1 SAR mission that provides open access images with unprecedented spatial coverage and at a weekly temporal resolution. Sentinel-1 InSAR is complemented with results based on the high spatial resolution TerraSAR-X images. The advantages and limitations of InSAR in the scope of periglacial research are discussed based on case studies in central and western Spitsbergen (Svalbard) and in Troms and Finnmark (Northern Norway).
In Papers I–V, we demonstrate the ability of InSAR to document the kinematic properties of the periglacial ground dynamics, characterised by displacement rates ranging from a millimetre to a metre over a season or a year. InSAR allows for investigating the displacement progression caused by the ground freeze–thaw cycles in permafrost lowlands and the gradual downslope creep of periglacial landforms in mountainous environments. InSAR observations are compared with in-situ measurements and geomorphological mapping, and coupled with statistical and physical modelling. This integration contributes to a better understanding of the factors controlling the spatio-temporal patterns of the ground movement.
This research suggests novel ways to develop dedicated InSAR products relevant for the assessment of geohazards and the systematic observation of ground dynamics in the context of climate change. The results show the value of combining satellite InSAR with complementary remote sensing techniques to document fast-moving landforms and provide decadal time series. Finally, this dissertation outlines perspectives for furthering the work in the scope of InSAR applied to periglacial research
Characterizing slope processes along the Piggtind mountain ridge, using 2D InSAR
Full text linkLarge rock slope deformations potentially evolving into catastrophic rock avalanches pose an eminent threat to the Norwegian society. A comprehensive characterization of their kinematic behavior, progressive slope development, and current deformation rates are thus required for hazard management. Njunnás and Piggtind/Skulvatindane are two adjacent rock slopes located in Troms County, Norway. Both slopes show morphological features diagnostic for rock slope deformations (RSD) and are, therefore, inventoried as unstable mountains by Geological Survey of Norway (NGU). However, a satisfying understanding of the RSDs are currently lacking. On Piggtind/Skulvatindane, the complex deformation morphology including substantial disintegration of rock and the high presence of superficial and periglacial slope processes partially obscure the deeper rock slope deformation. Hence, accomplishing a robust characterization of the RSD is not trivial and requires a detailed categorization of the slope processes.
In this study, two-dimensional satellite Interferometric Synthetic Aperture Radar (2D InSAR) is integrated with geomorphological- and structural investigations. By combining overlapping InSAR data obtained from both ascending and descending acquisition geometries, 2D InSAR surface displacements are estimated, allowing for quantification of all components of the displacement in the vertical E-W plane (horizontal, vertical, combined 2D velocity, and dip of combined 2D velocity vector). The 2D InSAR results and geological interpretations are displayed on maps and plotted along topographic profiles, allowing for detailed visualization.
Longitudinal variations in velocity and dip of combined 2D velocity vectors highlight a sliding-motion parallel to measured foliation on Njunnás, suggesting that the pre-existing, moderately inclined foliation planes are utilized as the basal rupture surface. A marked reduction in the dip of the combined 2D velocity vectors and increased brittle fracturing is observed in the lower sections of both RSDs, indicating an abrupt transition to a low-inclined basal rupture surface. Hence, both RSDs are classified as compound bi-planar slides. The RSD at Njunnás is interpreted to deform as a coherent single body due to the detected homogeneous 2D InSAR displacement rates in the order of 2–3 mm/yr. Contrary, the RSD at Piggtind/Skulvatindane generally exhibits displacement rates around 10 mm/yr but comprises large spatial variability of differential velocity. Clusters of high velocity (up to 157 mm/yr) have been interpreted to predominantly correspond to displacement of superficial mass-wasting deposits, solifluction features, and a multi-lobate rock glacier complex superimposed on the RSD.
These results highlight the advantage of characterizing RSDs and identifying superficial slope processes with a multidisciplinary approach, combining structural geology, geomorphology, and satellite remote sensing. The utilized approach is readily applicable to other RSDs when well covered with two complementary InSAR geometries and can be exploited to attribute a failure mechanism and state-of-activity to all inventoried RSDs at a regional or national scale
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
Space-Borne and Ground-Based InSAR Data Integration: The Åknes Test Site
Full text linkThis work concerns a proposal of the integration of InSAR (Interferometric Synthetic Aperture Radar) data acquired by ground-based (GB) and satellite platforms. The selected test site is the Åknes rockslide, which affects the western Norwegian coast. The availability of GB-InSAR and satellite InSAR data and the accessibility of a wide literature make the landslide suitable for testing the proposed procedure. The first step consists of the organization of a geodatabase, performed in the GIS environment, containing all of the available data. The second step concerns the analysis of satellite and GB-InSAR data, separately. Two datasets, acquired by RADARSAT-2 (related to a period between October 2008 and August 2013) and by a combination of TerraSAR-X and TanDEM-X (acquired between July 2010 and October 2012), both of them in ascending orbit, processed applying SBAS (Small BAseline Subset) method, are available. GB-InSAR data related to five different campaigns of measurements, referred to the summer seasons of 2006, 2008, 2009, 2010 and 2012, are available, as well. The third step relies on data integration, performed firstly from a qualitative point of view and later from a semi-quantitative point of view. The results of the proposed procedure have been validated by comparing them to GPS (Global Positioning System) data. The proposed procedure allowed us to better define landslide sectors in terms of different ranges of displacements. From a qualitative point of view, stable and unstable areas have been distinguished. In the sector concerning movement, two different sectors have been defined thanks to the results of the semi-quantitative integration step: the first sector, concerning displacement values higher than 10 mm, and the 2nd sector, where the displacements did not exceed a 10-mm value of displacement in the analyzed period
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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