1,720,975 research outputs found
Ship detection and tracking from ocean-bottom seismometer observations
No full textDans le cadre de l'expérience RHUM-RUM (Réunion Hotspot and Upper Mantle - Unterer Mantel Meetings), 57 sismomètres ont été déployés autour de l'île de la Réunion. L'analyse des enregistrements montre que ces instruments ont enregistré de nombreux signaux identifiés comme étant dus aux passages des navires. A partir des archives des trajectoires des navires ayant croisé dans l'Océan Indien non loin de ces instruments, cette thèse développe des méthodes visant à détecter et localiser des sources acoustiques dans une gamme de fréquence frontière entre le domaine de la sismologie et de l'acoustique sous-marine (1-50 Hz). Un premier travail de calibration des sismomètres pour cette tâche est développé et se base sur la connaissance de la trajectoire des navires pour retrouver l'orientation et la localisation exacte des instruments au fond de l'océan. Cette tâche est par nature difficile lors du déploiement et nécessite souvent des méthodes chronophages. Une méthode de détection et de suivi applicable aux navires marchands passant à moins de 100 kilomètres est ensuite mise au point. Cette méthode est adaptable à d'autres sources acoustiques océaniques comme les baleines. Pour reconstituer les trajectoires de sources acoustiques, ce travail s'appuie sur : une étude détaillée de la propagation des ondes par trajets multiples de la surface des océans à leur fond ; l'utilisation combinée du sismomètre à trois composantes et de l'hydrophone comme capteur acoustique vectoriel ; des méthodes capables de traiter des signaux continus et intrinsèquement aléatoires tel le bruit émis par les navires. L'utilisation d'une approche Bayésienne permet la construction de détecteurs optimaux au regard des a priori physiques et statistiques disponibles. Cette thèse inaugure l'étude du bruit des navires par les sismomètres de fond de mer en deux manières. Le bruit des navires peut être utilisé comme une source d'opportunité et permet des inversions sur les paramètres d'intérêt. Les sismomètres de fond de mer peuvent être utilisés comme observateurs passifs des océans et servir d'outil de surveillance maritime.Within the framework of the RHUM-RUM (Réunion Hotspot and Upper Mantle - Unterer Mantel Meetings) experiment, 57 seismometers have been deployed around La Réunion Island. The analysis of the recordings shows that these instruments recorded many signals identified as being due to the passage of ships. Based on the archives of the trajectories of ships crossing in the Indian Ocean, this thesis develops methods aiming at detecting and locating acoustic sources in a frequency range located between the field of seismology and underwater acoustics (1-50 Hz). A first work of calibration of the seismometers for this task is developed and is based on the knowledge of the trajectory of ships to find the orientation and the exact localization of the devices on the bottom of the ocean. This task is by nature difficult when deploying this type of device and often requires time-consuming methods. A detection and tracking method applicable to merchant ships passing less than 100 kilometres away is then developed. This method is adaptable to other oceanic acoustic sources such as whales. To reconstruct the trajectories of acoustic sources, this work is based: on a detailed study of the multi-path propagation of waves from the surface of the oceans to their bottom; on the combined use of the three-component seismometer and the hydrophone as an acoustic vector-sensor; on methods capable of dealing with continuous and inherently random signals such as the noise emitted by ships. The use of a Bayesian approach allows the construction of optimal detectors with regard to the physical and statistical a priori available. This thesis inaugurates the study of ship noise by seafloor seismometers in two ways. Ship noise can be used as a source of opportunity and allows inversions on parameters of interest. Seafloor seismometers can be used as ocean passive observers and can serve as maritime surveillance tools
Détection et suivi de navires par des observations sismologiques et hydroacoustiques de fond de mer
No full textWithin the framework of the RHUM-RUM (Réunion Hotspot and Upper Mantle - Unterer Mantel Meetings) experiment, 57 seismometers have been deployed around La Réunion Island. The analysis of the recordings shows that these instruments recorded many signals identified as being due to the passage of ships. Based on the archives of the trajectories of ships crossing in the Indian Ocean, this thesis develops methods aiming at detecting and locating acoustic sources in a frequency range located between the field of seismology and underwater acoustics (1-50 Hz). A first work of calibration of the seismometers for this task is developed and is based on the knowledge of the trajectory of ships to find the orientation and the exact localization of the devices on the bottom of the ocean. This task is by nature difficult when deploying this type of device and often requires time-consuming methods. A detection and tracking method applicable to merchant ships passing less than 100 kilometres away is then developed. This method is adaptable to other oceanic acoustic sources such as whales. To reconstruct the trajectories of acoustic sources, this work is based: on a detailed study of the multi-path propagation of waves from the surface of the oceans to their bottom; on the combined use of the three-component seismometer and the hydrophone as an acoustic vector-sensor; on methods capable of dealing with continuous and inherently random signals such as the noise emitted by ships. The use of a Bayesian approach allows the construction of optimal detectors with regard to the physical and statistical a priori available. This thesis inaugurates the study of ship noise by seafloor seismometers in two ways. Ship noise can be used as a source of opportunity and allows inversions on parameters of interest. Seafloor seismometers can be used as ocean passive observers and can serve as maritime surveillance tools.Dans le cadre de l'expérience RHUM-RUM (Réunion Hotspot and Upper Mantle - Unterer Mantel Meetings), 57 sismomètres ont été déployés autour de l'île de la Réunion. L'analyse des enregistrements montre que ces instruments ont enregistré de nombreux signaux identifiés comme étant dus aux passages des navires. A partir des archives des trajectoires des navires ayant croisé dans l'Océan Indien non loin de ces instruments, cette thèse développe des méthodes visant à détecter et localiser des sources acoustiques dans une gamme de fréquence frontière entre le domaine de la sismologie et de l'acoustique sous-marine (1-50 Hz). Un premier travail de calibration des sismomètres pour cette tâche est développé et se base sur la connaissance de la trajectoire des navires pour retrouver l'orientation et la localisation exacte des instruments au fond de l'océan. Cette tâche est par nature difficile lors du déploiement et nécessite souvent des méthodes chronophages. Une méthode de détection et de suivi applicable aux navires marchands passant à moins de 100 kilomètres est ensuite mise au point. Cette méthode est adaptable à d'autres sources acoustiques océaniques comme les baleines. Pour reconstituer les trajectoires de sources acoustiques, ce travail s'appuie sur : une étude détaillée de la propagation des ondes par trajets multiples de la surface des océans à leur fond ; l'utilisation combinée du sismomètre à trois composantes et de l'hydrophone comme capteur acoustique vectoriel ; des méthodes capables de traiter des signaux continus et intrinsèquement aléatoires tel le bruit émis par les navires. L'utilisation d'une approche Bayésienne permet la construction de détecteurs optimaux au regard des a priori physiques et statistiques disponibles. Cette thèse inaugure l'étude du bruit des navires par les sismomètres de fond de mer en deux manières. Le bruit des navires peut être utilisé comme une source d'opportunité et permet des inversions sur les paramètres d'intérêt. Les sismomètres de fond de mer peuvent être utilisés comme observateurs passifs des océans et servir d'outil de surveillance maritime
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
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
Sensing Optical Fibers for Earthquake Source Characterization Using Raw DAS Records
No full textInternational audienceAbstract Distributed Acoustic Sensing (DAS) is becoming a powerful tool for earthquake monitoring, providing continuous strain‐rate records of seismic events along fiber optic cables. However, the use of standard seismological techniques for earthquake source characterization requires the conversion of data in ground motion quantities. In this study we provide a new formulation for far‐field strain radiation emitted by a seismic rupture, which allows to directly analyze DAS data in their native physical quantity. This formulation naturally accounts for the complex directional sensitivity of the fiber to body waves and to the shallow layering beneath the cable. In this domain, we show that the spectral amplitude of the strain integral is related to the Fourier transform of the source time function, and its modeling allows to determine the source parameters. We demonstrate the validity of the technique on two case‐studies, where source parameters are consistent with estimates from standard seismic instruments in magnitude range 2.0–4.3. When analyzing events from a 1‐month DAS survey in Chile, moment‐corner frequency distribution shows scale invariant stress drop estimates, with an average of Δ σ = (0.8 ± 0.6) MPa. Analysis of DAS data acquired in the Southern Apennines shows a dominance of the local attenuation that masks the effective corner frequency of the events. After estimating the local attenuation coefficient, we were able to retrieve the corner frequencies for the largest magnitude events in the catalog. Overall, this approach shows the capability of DAS technology to depict the characteristic scales of seismic sources and the released moment
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