1,721,011 research outputs found
Autochthon vs. blended wines: Do objective and sensory characteristics matter?
No full textWorking Paper Series, Università Piemonte Oriental
Sea surface slicks measured by SAR
Full text linkThe Synthetic Aperture Radar (SAR) system capability to detect and characterise marine surface slicks was tested during the SAR-580 experiment in the northern Adriatic Sea, offshore the Venice coast, in October 1990. Two small artificial slicks of oleyl alcohol were produced in an area around the oceanographic platform of the Italian National Research Council (CNR). The oleyl alcohol produces a damping of the sea centimetric waves, which has been measured by an airborne two band (C and X) SAR, by a tower based 3 band (L, S and C) scatterometer and by a wave gauge, installed on board the platform, which measures the instantaneous sea surface elevation in the range from gravity up to capillary waves. The good agreement among measures proves that multi-frequency SAR is able to detect and characterise sea surface films. Slicks in SAR images taken during SIR-C/X-SAR mission in 1994 have been analysed on the basis of these results and L-band measurements of spatial attenuation near the borders of the slicks have been done, in order to test the slicks detectability using single-band SAR images
SAR detection and characterization of sea surface slicks
No full textIn this paper we demonstrate SAR system capability for detecting and characterizing marine surface slicks. During an aircraft measurement campaign over the Gulf of Genoa (Italy), a multi-frequency SAR system, operating in P-, L- and C-bands, explored a sea area heavily covered by slicks. At the same time in situ measurements were performed with an interferential microwave probe, installed on board a small boat, capable of measuring high resolution sea spectra up to frequencies of capillary waves. By plotting SAR pixel intensity versus sea wave Bragg frequency we obtained wide portions of the sea spectrum region affected by the surface film damping. Spectra derived from SAR imagery and from gauge data present comparable slopes and furthermore the ratio between clean to slicked water spectrum obtained with the two techniques were surprisingly similar. This demonstrates the multi-frequency SAR systems ability to detect and characterize sea surface films assuming the Bragg mechanism in the radar back-scatter. The outlined analysis suggests a simple methodology to monitor coastal water quality by using airborne SAR
Wind stress structure in the unstable marine surface layer detected by SAR
No full textThe wind stress in the marine surface layer under unstable conditions and low wind speed has been studied using a Synthetic Aperture Radar (SAR) image of the sea surface and time series of the horizontal and vertical wind velocities and of the wind stress recorded on board the C.N.R. research platform, in the northern Adriatic Sea, during a SAR overflight. A conditional sampling technique has been used on the wind stress time series and on the SAR image to detect downward (sweep) and upward (ejection) bursts of the momentum flux, as well as the two-dimensional structure of the radar backscatter. From the ensemble average of both the wind stress and the backscatter structures, it has been possible to estimate the mean duration of the upward (≈11 s) and the downward (≈15 s) wind stress bursts and the mean size of the bright patches of the SAR image (≈120 m). The front of the mean backscatter structure, associated with the downward wind stress bursts, has been related to the time length of the mean sweep stress structure to get, after accounting for a threshold of the wind stress for the generation of the sea surface wavelets, the translation velocity Ut of the mean wind stress of sweep, very close to the mean wind speed. The vertical coherence of the wind stress structures has permitted to refer the translation velocity to a level very close to the sea surface, but above the viscous sublayer. The variability of Ut with height has been studied through comparison with the mean wind speed at different heights z calculated by a boundary-layer model. Accounting for the results reported in the literature, there is an indication that Ut is constant with height in the range 0.5 m ≤ z ≤ 15 m. The two-dimensional pattern of the wind stress structures has been derived from the SAR image. The structures appear elongated crosswind, as with microfronts, with an average cross- to down-wind ratio of ≈ 4. The area covered by the downward wind stress structures represents 13% of the total area
Oil spill detection using marine SAR images
No full textA probabilistic approach to distinguish oil spills from other similar oceanic features in marine Synthetic Aperture Radar (SAR) images has been developed and tested. The method uses statistical information obtained from previous measurements of physical and geometrical characteristics for both oil spill and natural features. A sample image is evaluated using two different procedures to determine the probability that it is an oil spill, the results of the two procedures are then compared. The classification-algorithm performance was evaluated using a test dataset containing 80 examples that were oil spills and 43 that were natural features exhibiting characteristics similar to oil spills: more than 80% of the samples were classified correctly. The reliability of the method was then determined using a new dataset and similar results were obtained.
A probabilistic approach to distinguish oil spills from other similar oceanic features in marine Synthetic Aperture Radar (SAR) images has been developed and tested. The method uses statistical information obtained from previous measurements of physical and geometrical characteristics for both oil spill and natural features. A sample image is evaluated using two different procedures to determine the probability that it is an oil spill, the results of the two procedures are then compared. The classification-algorithm performance was evaluated using a test dataset containing 80 examples that were oil spills and 43 that were natural features exhibiting characteristics similar to oil spills: more than 80% of the samples were classified correctly. The reliability of the method was then determined using a new dataset and similar results were obtained
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
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