1,720,995 research outputs found
Control of the repeatability of high frequency multibeam echosounder backscatter by using natural reference areas
No full textThe increased use of backscatter measurements in time series for environmental monitoring necessitates the comparability of individual results. With the current lack of pre-calibrated multibeam echosounder systems for absolute backscatter measurement, a pragmatic solution is the use of natural reference areas for ensuring regular assessment of the backscatter measurement repeatability. This method mainly relies on the assumption of a sufficiently stable reference area regarding its backscatter signature. The aptitude of a natural area to provide a stable and uniform backscatter response must be carefully considered and demonstrated by a sufficiently long time-series of measurements. Furthermore, this approach requires a strict control of the acquisition and processing parameters. If all these conditions are met, stability check and relative calibration of a system are possible by comparison with the averaged backscatter values for the area. Based on a common multibeam echosounder and sampling campaign completed by available bathymetric and backscatter time series, the suitability as a backscatter reference area of three different candidates was evaluated. Two among them, Carré Renard and Kwinte, prove to be excellent choices, while the third one, Western Solent, lacks sufficient data over time, but remains a valuable candidate. The case studies and the available backscatter data on these areas prove the applicability of this method. The expansion of the number of commonly used reference areas and the growth of the number of multibeam echosounder controlled thereon could greatly contribute to the further development of quantitative applications based on multibeam echosounder backscatter measurements
Interpreting monitoring data for shoreline and geohazard mapping
Get PDFThe demand for marine-related spatial information has become increasingly apparent in recent years at a European and national scale, due to the increased pressures on the sea-floor environments and marine resources of UK territorial waters. The advent of economically viable swath bathymetry data acquisition in the coastal zone and effective collaborative partnerships between the Channel Coastal Observatory, Maritime and Coastguard Agency, UK Hydrographic Office, British Geological Survey and academic institutions, have opened up new opportunities to produce a robust scientific evidence base to inform integrated coastal zone management objectives and contribute to wider scientific initiatives. Interpretation of high-quality bathymetric data, acoustic backscatter and ground-truthing data allows zones of exposed bedrock, rock outcrops and pinnacles to be identified, along with areas of mobility or stability of surficial sediments. Temporal and spatial analyses of coastal and marine monitoring datasets also contribute to improved understanding of interactions between natural coastal process and coastal-defence and beach-management operations. Furthermore, developments in three-dimensional mapping techniques and visualisation technologies have enabled seamless high-resolution coastal geology maps to be re-interpreted and extended offshore, providing a more complete picture of the baseline geology, physical properties, structure and geohazards in the coastal and nearshore zone. The full paper details the methodology developed to produce a range of indicative marine mapping layers, and presents examples from eastern and southern England where marine-related spatial data has contributed to the multi-disciplinary scientific evidence base to inform development of UK marine policy and planning, coastal management and coastal zone geological mapping
Marine Geophysical Investigation of the Chain Fracture Zone in the Equatorial Atlantic From the PI‐LAB Experiment
Get PDFThe Chain Fracture Zone is a 300 km long transform fault that offsets the Mid Atlantic Ridge. We analysed new multibeam bathymetry, backscatter, gravity and magnetic data with 100 % multibeam bathymetric data over the active transform valley and adjacent spreading segments as part of the Passive Imaging of the Lithosphere Asthenosphere Boundary (PI‐LAB) Experiment. Analyses of these data sets allow us to determine the history and mode of crustal formation and the tectonic evolution of the transform system and adjacent ridges over the past 20 M.y. We model the total field magnetic anomaly to determine the age of the crust along the northern ridge segment to better establish the timing of the variations in the seafloor fabric and the tectonic‐magmatic history of the region. Within the active transform fault zone, we observe 4 distinct positive flower structures with several en échelon fault scarps visible in the backscatter data. We find up to ‐10 mGal residual Mantle Bouguer Anomaly in the region of the largest positive flower structure within the transform zone suggesting crustal thickening relative to the crustal thinning typically observed in fracture zones in the Atlantic. The extensional/compressional features observed in the Chain Transform are less pronounced than those observed further north in the Vema, St Paul and Romanche and may be due to local ridge segment adjustments
Multibeam bathymetry raw data (Kongsberg EM 12 entire dataset) of RV CHARLES DARWIN during cruise CD168
No full textRaw multibeam bathymetry data were collected aboard RV Charles Darwin during cruise CD168 using a Kongsberg EM12 multibeam echosounder. This is a 13kHz echosounder with beamwidths of 1.8° and 3.5° with 81 beams in total. The expedition took place during 2.2.2005 and 16.2.2005 from Las Palmas, Spain to Mindelo, Cape Verde in the Atlantic Ocean. Data were recorded specifically within the Cabo Verde Exclusive Economic Zone (EEZ) and outside EEZs at an average depth of approximately 2000m. The main aim of CD168 was to carry out an initial reconnaissance survey of the influence of landsliding on the Cape Verde islands, in the eastern central Atlantic, in an area where subaerial evidence suggests the occurrence of landslides but where limited previous offshore work had been undertaken. There is no information about sound velocity correction made. Data are unprocessed and can therefore contain incorrect depth measurements (artifacts) if not further processed. Note that refraction errors can be expected due to the lack of proper SVP. The data are stored at the British Oceanographic Data Centre (BODC) and have been submitted to PANGAEA database for data curation and publication
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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