1,720,984 research outputs found
A retrospective analysis of the Shinmoedake (Japan) eruption of 26–27 January 2011 by means of Japanese geostationary satellite data
Full text linkDuring the sub-plinian eruptions of Mt. Shinmoedake (Japan) on 26–27 January 2011 a significant amount of ash
was emitted into the atmosphere, destroying thousands of hectares of farm land, causing air traffic disruption,
and forcing the closure of four railroad lines located around the volcano. In this work, a retrospective analysis
of these eruptive events is presented, exploiting the high temporal resolution of the Japanese Multi-functional
Transport Satellites (MTSAT) data to study thermal volcanic activity, to identify and track volcanic ash, and to determine
the cloud-top height, inferring information about eruption features and space-time evolution. We show
that a strong and sudden increase in the thermal signal occurred at Mt. Shinmoedake as a consequence of above
mentioned eruptive events, generating hot spots timely detected by the RSTVOLC algorithm for the first time implemented
here on data provided by geostationary satellites. This study also shows that the emitted ash plume,
identified by means of the RSTASH algorithm, strongly fluctuated in altitude, reaching a maximum height around
7.4 km above sea level, in agreement with information provided by the Tokyo VAAC. The plume heights derived
in this work, by implementing the widely accepted cloud-top temperature method, appear also compatible with
the values provided by independent weather radar measurements, with the main differences characterizing the
third sub-plinian event that occurred in the afternoon of 27 January. The estimates of discharge rate, the temporal
trend of ash affected areas, and the results of thermal monitoring reported in this work seem to indicate that the
third sub-plinian event was the least intense. In spite of some limitations, this study confirms the potential of
Japanese geostationary satellites in effectively monitoring volcanoes located in the West Pacific region, providing
continuous information also about such critical parameters of ash clouds as the plume height. Such information is
useful not only for driving numerical models, forecasting ash dispersion into the atmosphere, but also for characterizing
eruption features and dynamics
Implementation of a Robust Satellite Technique (RST ASH) On Msg-Seviri Data for timely detection and near real- time monitoring of volcanic ash clouds from space
No full textThe RSTASH algorithm is a specific configuration of the Robust Satellite Techniques (RST) multitemporal approach developed for detecting and tracking ash clouds from space. This algorithm was originally proposed and tested with success on AVHRR (Advanced Very High Resolution Radiometer) and MODIS (Moderate Resolution Imaging Spectroradiometer) data, and has been recently implemented on data provided by Japanese geostationary satellites (MTSAT). In this work, the preliminary results achieved exporting RSTASH on MSG-SEVIRI (Meteosat Second Generation - Spinning Enhanced Visible and Infrared Imager) data to study the Eyjafjallajökull eruptions of April- May 2010, which caused an unprecedented air traffic disruption in Northern and central Europe, are reported. This study was carried testing RSTASH in critical observational conditions (e.g. high view angles, cold background, frequent and diffuse cloud coverage), using for the first time an optimized configuration of this algorithm for daytime conditions, and assessing its potential in monitoring ash clouds in real time, exploiting the high temporal resolution of SEVIRI (15 minutes). Outcomes of this work show that RSTASH may be profitably used for an automated and accurate identification of ashaffected areas also at high latitude regions. Accurate detection, in fact, is a mandatory step before to characterize ash clouds from a quantitative point of view by means of retrieval analyses. These results encourage a full implementation of this algorithm on SEVIRI data, in view of a its possible usage in operational contexts
Investigating Volcanic Plumes from Mt. Etna Eruptions of December 2015 by Means of AVHRR and SEVIRI Data
Full text linkIn early December 2015, a rapid sequence of strong paroxysmal events took place at the Mt. Etna crater area (Sicily, Italy). Intense paroxysms from the Voragine crater (VOR) generated an eruptive column extending up to an altitude of about 15 km above sea level. In the following days, other minor ash emissions occurred from summit craters. In this study, we present results achieved by monitoring Mt. Etna plumes by means of RSTASH (Robust Satellite Techniques-Ash) algorithm, running operationally at the Institute of Methodologies for Environmental Analysis (IMAA) on Advanced Very High Resolution Radiometer (AVHRR) data. Results showed that RSTASH detected an ash plume dispersing from Mt. Etna towards Ionian Sea starting from 3 December at 08:40 UTC, whereas it did not identify ash pixels on satellite data of same day at 04:20 UTC and 04:40 UTC (acquired soon after the end of first paroxysm from VOR), due to a mixed cloud containing SO2 and ice. During 8−10 December, the continuity of RSTASH detections allowed us to estimate the mass eruption rate (an average value of about 1.5 × 103 kg/s was retrieved here), quantitatively characterizing the eruptive activity from North East Crater (NEC). The work, exploiting information provided also by Spinning Enhanced Visible and Infrared Imager (SEVIRI) data, confirms the important contribution offered by RSTASH in identifying and tracking ash plumes emitted from Mt. Etna, despite some operational limitations (e.g., cloud coverage). Moreover, it shows that an experimental RST product, tailored to SEVIRI data, for the first time used and preliminarily assessed here, may complement RSTASH detections providing information about areas mostly affected by volcanic SO2
Thermal Monitoring of Eyjafjöll Volcano Eruptions by Means of Infrared MODIS Data
No full textIn the evening of 20 March 2010, after about two centuries of quiescence, an effusive eruption took place at Eyjafjöll (Iceland) volcano, from a small vent localized on the northeast flank (Fimmvörduháls Pass) of the volcano edifice. On 31 March, a new eruptive fissure opened on the same region emitting lava. About 2 weeks later, on 14 April, a strong explosive eruption took place under the Eyjafjallajökull glacier, injecting copious amounts of ash in the atmosphere and causing an unprecedented air traffic disruption in Northern and Central Europe. In this paper, the changes in thermal signals occurring at Eyjafjöll volcano during 1 March-20 April 2010 are investigated, testing the RSTVOLC algorithm for the first time in a subpolar environment. Outcomes of this retrospective study, performed by means of infrared Moderate Resolution Imaging Spectroradiometer (MODIS) data, show that both effusive and explosive eruptions of the Eyjafjöll volcano could be identified in a timely manner and well monitored from space. Moreover, in spite of a lack of pre-eruptive hot spots detection, this paper reveals a general increasing trend of the middle infrared signal at crater area, beginning 2 weeks before the explosion, stimulating and suggesting further investigations devoted to better characterize the thermal behavior of the monitored volcano
Implementation of the RST (Robust Satellite Techniques) approach on MSG-SEVIRI data: applications for volcanic activity monitoring
No full textThe Robust Satellite Techniques (RST) is a multitemporal approach of satellite data analysis proposed to study different natural/environmental hazards, including high risk volcanic phenomena. In particular, both thermal features and ash emissions may be investigated by RST, by using two specific configurations of such an approach. These algorithms have been tested on different volcanic areas exploiting data provided by polar satellite sensors, such as the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), showing a high trade-off between reliability and sensitivity of detection. In this work, the RST exportability on data provided by the Spinning Enhanced Visible Infrared Imager (SEVIRI), onboard Meteosat Second Generation (MSG) satellites, is assessed, by studying some recent eruptive events of Etna (Italy) and Grimsvotn (Iceland) volcanoes. Outcomes of this work confirm that the RST-based algorithms may give an important contribution for mitigating volcanic hazards during major eruptions, especially in the framework of integrated and automated early warning systems
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
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