1,720,957 research outputs found
On the incidence angle dependence of synthetic aperture radar co-polarisation sea surface signature
No full textIn this study, the behaviour of co-polarisation sea surface signature is analysed with respect to L-band airborne synthetic aperture radar incidence angle under low-to-moderate sea state. The sensitivity of polarised and unpolarised backscat-tering component to changes in incidence angles is investigated. When dealing with the polarised part, the scattering behaviour of horizontal, vertical and circular polarisations are considered while the normalised pedestal height is evaluated as estimator of the amount of unpolarised power scattered off sea surface.Experimental results suggest that: 1) deviation from Bragg scattering occurs at lower and higher incidence angles; 2) backscattering at vertical polarisation keeps constant while backscattering at horizontal (circular) polarisation decreases (increases) with incidence angle; 3) the pedestal height of the co-polarisation sea surface signature remarkably increases when the incidence angle increases, with the largest variation observed at lower angles of incidence
Multi-Frequency and Multi-Polarisation Analysis of the Scattering From Offshore Wind Turbines
No full textIn this study, a scattering analysis of wind turbines is performed using a multi-frequency and multi-polarisation synthetic aperture radar dataset. The latter includes L-, C- and X-band synthetic aperture radar imagery collected by Alos PalSAR-2, Sentinel-1 and PAZ, respectively. Multi-polarization normalized radar cross sections and reflecion symmetry are considered to characterize the backscattering properties of the Robin Rigg offshore wind farm (Solway Firth, UK) turbines, whose features are evaluated with reference to a target-free surrounding sea surface. The experimental results show that the detectability of the wind turbines is severely influenced by the incident wavelength, with the reflection symmetry being a robust and effective parameter to characterize wind turbines. Co-polarized backscattering is always larger than the corresponding cross-polarized one at that HH-polarized backscattering is larger at L-band rather than at X-band, while the C-band VV-polarized backscattering is the lowest. Considering cross-polarized channel, wind turbines call for the largest (lowest) backscattering at X-band (C-band). Results also show that wind turbines are characterized by a correlation between co- and cross-polarized channels much larger than the surrounding sea surface, which satisfies reflection symmetry. In particular, the HH-HV correlation is, on average, larger at X-rather than L-band, while the C-band VV-VH correlation is much lower
Multi-band scattering analysis of offshore wind turbines using dual-polarized SAR measurements
No full textThis study investigates the scattering properties of wind turbines, utilizing synthetic aperture radar datasets collected by ALOS PALSAR-2, RADARSAT-2, and PAZ satellite missions. The radar imagery spans L-, C- and X-band frequencies keeping almost the same incidence angle and pixel spacing. Focused on the Robin Rigg offshore wind farm in Solway Firth, UK, the analysis deals with assessing backscattering properties through multi-polarization, i. e., co- and cross-polarized, normalized radar cross-sections and reflection symmetry. The study evaluates the features of the turbines in relation to a target-free surrounding sea surface. The experimental results indicate that the incident wavelength and the relative orientationsignificantly impacts the detectability of wind turbines. Additionally, reflection symmetry is identified as a reliable and effective parameter for characterizing wind turbines backscattering. The results also suggest that increasing (decreasing) the incident wavelength increases (reduces) the co-polarized backscattering and the co-/cross-polarized correlation of wind turbines
SAR beyond the spatial resolution limit
No full textIn this paper, the Synthetic Aperture Radar (SAR) image speckle over marine scenes is modelled and tested over Sentinel-1 single-look complex dual-polarimetric measurements at variance of wind speed. The aim of the study is to demonstrate that SAR speckle is informative once a proper physical/statistical speckle model is developed. The first-order statistical distribution of the speckle is analyzed by means of the Normalized Intensity Moments (NIMs) under three different cases: low, moderate and high wind conditions.Experimental results show that over VV-polarized images the K-distribution model works very well under low-to-moderate wind regime, while at increasing wind speed a new speckle model has to be developed and considered since a very different scattering mechanism applies over sea surface
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
Spatio-temporal variability coastline analysis using C-band dual-polarimetric synthetic aperture radar measurements
No full textThis study demonstrates the effectiveness of C-band synthetic aperture radar satellite data in coastline extraction and coastal erosion monitoring. The research is based on a significant dataset collected along the Ionian coast of the Basilicata region in southern Italy. Preliminary results highlight the enhanced value of integrating spaceborne radar sensor technologies in the context of coastal area observation and management
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
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