1,721,007 research outputs found
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
Resolution enhancement of polarimetric images using a high resolution mono-channel image
No full textInternational audiencePolarimetric SAR images provide information about the scattering mechanisms that increases the capacity of urban areas analysis. However, due to technological constraint, their resolution is often coarser than the resolution of single channel SAR images. To overcome this, we propose a resolution enhancement algorithm for polarimetric images using a mono-channel SAR image acquired in interferometric condition. This algorithm is based on the spectral properties of point-like scatterers. It is tested on airborne and spaceborne data. The point-like scatterers are well focused and their polarimetric and interferometric behaviours are preserved
Traitements cohérents d’images RSO multi-modes multi-resolutions pour la caractérisation du milieu urbain
No full textThe refinement of Synthetic Aperture Radar (SAR) imagery makes the monitoring of urban areas possible. Different acquisition modes of multivariate SAR images are available, such as the polarimetric mode that gives information about the nature or the geometry of imaged objects, or the interferometric mode that enables the measure of their height or the displa- cement between two acquisitions. However, all the acquisition modes do not reach the same spatial resolution. The major goal of this work was to combine polarimetric images and a mono-channel high-resolution image to create high resolution polarimetric images with the same properties as the initial polarimetric image.This work started with the study of covariance matrices estimation from which meaningful parameters linkable to physical infor- mation, such as the phase, can be extracted. We first showed that the variance is not adapted to describe the fluctuations of the estimated phase. We proposed a directional statistics indicator to describe the estimated phase fluctuations, whichever the definition interval of the phase. This indicator can be used to separate two populations of pixels with different phase fluctuations or to compare the measured phase to a modeled phase. We also showed that the resolution has an impact on the covariance matrix estimation, because it restrains the size of the sample of pixels which values can be considered as independent and identically distributed for the covariance matrix estimation.We chose to model the urban scatterers as a combination of randomly responding scatterers and deterministic bright point-like scatterers. The values of the pixels representing the random scatterers are modeled following the fully developed speckle ; the point-like scatterers are supposed to be white and isotropic. The Pol-Sharpening algorithms that we developed are based on the point-like scatterers spectral properties. One of the key issue is to have a sufficient sample size in order to limit the fluctuation of the polarimetric information estimation without introducing mixing. The chosen spectral method enables to focalize the point- like scatterers, i.e. to refine the resolution, while preserving their polarimetric and interferometric properties. If the developed algorithms keep the value of intensity and phase of the pixels included in homogeneous speckle areas, they modify their statistical parameters.Finally, we studied the measure of the height and the deformation of the Eiffel Tower and three other towers on the Front de Seine in Paris using a temporal stack of 98 TerraSAR-X images acquired between 2008 and 2012. We showed that neglecting the deformation during the height measurement could result in outliers. Even though these outliers can be removed during the study of a temporal stack, it is still a limitation of the interferometry techniques on buildings. By measuring a monoscopic height, we could measure deformations up to four centimeters for the Eiffel Tower. These deformations do not present any seasonal trend contrary to the deformations measured on the Mirabeau Tower, which are minimal in winter and maximal in summer. Nevertheless, we neglected the impact of the atmosphere on the deformation measurement and this work hypothesis limits our measurement accuracy to the centimeter.Nous nous sommes intéressés à l’étude du milieu urbain par l’imagerie Radar à Synthèse d’Ouverture (RSO), rendue possible par l’amélioration des résolutions des images. Différents modes d’acquisition d’images RSO multi-variées sont possibles, comme la polarimétrie qui apporte des informations sur la nature et la géométrie des objets présents sur la scène et l’interférométrie qui permet d’en mesurer la hauteur ou le déplacement entre différentes acquisitions. Cependant, tous ces modes n’ont pas la même résolution. L’objectif de ce travail a été de combiner des images polarimétriques et des images mono-canales de résolution plus fine pour former des images de résolution fine conservant les propriétés polarimétriques et interférométriques des images originales.Nous avons commencé par étudier l’estimation des matrices de covariance des images qui permet l’extraction de paramètres tels que la phase, qui peuvent être reliés à des informations physiques. Nous avons tout d’abord montré que la variance n’est pas un indicateur statistique adapté pour décrire les fluctuations de la phase estimée. Nous avons alors proposé un indicateur basé sur la théorie des statistiques directionnelles qui permet de séparer deux populations de pixels dont les fluctuations de la phase sont différentes ou de comparer des phases mesurées à des phases simulées, quel que soit l’intervalle de définition de la phase. Nous avons aussi montré que la résolution impacte l’estimation des statistiques des images du milieu urbain en imposant des contraintes sur la taille de l’échantillon de pixels dont les valeurs peuvent être considérées comme indépendantes et identiquement distribuées pour l’estimation de la matrice de covariance.Nous avons modélisé les diffuseurs présents en milieu urbain en une combinaison de diffuseurs ayant un comportement aléatoire et des diffuseurs déterministes, ponctuels et très énergétiques appelés points-brillants. Les valeurs des pixels qui représentent les diffuseurs aléatoires sont modé- lisées selon le modèle de speckle pleinement développé ; les points-brillants sont supposés blancs et isotropes. Les algorithmes de raffinement de la résolution des images polarimétriques que nous avons développés sont fondés sur les propriétés spectrales de ces points-brillants. L’un des enjeux majeurs est d’utiliser un échantillon de taille suffisamment grande pour limiter la fluctuation de l’estimation des informations polari- métriques, sans introduire de mélange, tout en gardant les propriétés aléatoires du speckle. La méthode spectrale choisie permet d’assurer la focalisation des points-brillants et donc le raffinement de la résolution tout en préservant leurs informations polarimétriques et interférométriques. Si les algorithmes développés conservent bien les valeurs d’intensité et de phase des pixels des zones homogènes de speckle, ils en diminuent le degré d’aléatoire.Enfin, nous nous sommes intéressés à la mesure de la hauteur et de la déformation de la Tour Eiffel et de trois autres tours situées sur le Front de Seine, en utilisant une pile temporelle de 98 images TerraSAR-X acquises entre 2008 et 2012. Nous avons montré que négliger les déformations lors de la mesure de la hauteur peut résulter en des hauteurs aberrantes. Si ces hauteurs aberrantes peuvent être supprimées dans le cadre de l’étude d’une pile temporelle, elles sont néanmoins une limitation de la technique d’interférométrie sur des bâtiments. En mesurant une hauteur monoscopique, nous avons pu mesurer des déformations allant jusqu’à quatre centimètres pour la Tour Eiffel. Ces déformations ne présentent pas de tendance saisonnière contrairement aux déformations mesurées sur la Tour Mirabeau, qui sont minimale en hiver et maximale en été. Par contre, nous avons négligé l’impact de l’atmosphère dans la mesure de la déformation ce qui limite la précision de la mesure de la déformation au centimètre
Dense building deformation monitoring from InSAR based on LiDAR height measurement
No full textInternational audienceCreating digital twins of cities is essential to detect urban heat islands, or assess the risk of flooding. Incorporating the temporal axis, changes like urban spreading or urban renovation, can be encapsulated in the digital twins. At smaller scales, digital twins can also be used to follow the deformations of buildings that can be engendered by terrain movement due to subsidence or underground works. These deformation measurements can be extracted from InSAR temporal stack together with the building height [Weissgerber2017]. Moreover, InSAR acquisitions allow monitoring large areas with a bi-monthly update. However, the interpretation of the InSAR phase may be hindered by geometrical effects, such as layovers and shadows that are very present in dense urban environments. On the other hand, 3D description of buildings can be extracted from LiDAR point clouds with their fine height resolution and the large density of measured points. However, LiDAR acquisitions have a small footprint, requiring a large number of flights to monitor an entire city, leading to infrequent updates. In this work, our goal is to use LiDAR cloud points as a reference that can help disentangle the InSAR information, in order to extract information about building deformation. To do so, two steps are needed: 1. The geometrical alignment between the LiDAR point clouds and the SAR image to get a LiDAR reference height for each pixel of the studied buildings. This includes the selection of LiDAR points that corresponds to scatterers visible in the sar image. 2. The analysis of the InSAR phase temporal stack to detect deformation. The first step is to separate the contribution of the elevation in the InSAR phase and the contribution of the deformation. This is done by converting the reference altitude of each pixel found in step one to a reference phase for each InSAR acquisition. However, a phase difference that is due to the discrepancy between the phase scattering center height and the LiDAR geometry can be detecting since it is stable through time which the deformation pattern that changes with the acquisition. Then for InSAR pairs where deformation has been detected, the dense deformation pattern can be analyzed to detect non-uniform deformation across the building façade. This study is based on a temporal stack of 96 images acquired by TerraSAR-X/TanDEM-X between 2007 and 2012, with the reference image being chosen as the 24/01/2009. The LiDAR reference is the LiDAR HD acquired by IGN in 2023. Given the large time gap between the TerraSAR-X/TanDEM-X acquisition and the LiDAR HD one, we selected buildings with no structural changes between the two sources of data. Mainly, we focus on three buildings previously studied in [Weissgerber2017]: The Mirabeau Tower, The Cristal Tower and the Keller Tower. The footprint of the building is also supposed to be known. It is collected from the BD TOPO also produced by IGN. To align geometrically the LiDAR reference and the SAR images, we use the co-registration algorithm described in [Weissgerber2022] that enables to project each LiDAR point in the reference SAR image. Given the size of the LiDAR point cloud, we project only the LiDAR points that are classified as buildings in the building footprint. This enables removing the ground, vegetation points or artifacts that are labeled as such in the LiDAR point cloud. To select the LiDAR points that correspond to visible scatterers in the SAR image, the points are projected in the azimuth/range plane, without considering their height difference. Then, the visibility criteria are computed separately for each azimuth by assuming that the building façades are opaque. If the roof is visible, the points are considered as visible if their height is above the shadow cast by the points with a smaller range than theirs. If the roof is not visible, only the points having the smallest range are considered as visible. After having selected the LiDAR point visible in the SAR acquisition, all the SAR pixels may not have a height reference due to the scarcity of the LiDAR point cloud. To fill the gap in the façade, the height of the LiDAR points is linearly regressed between the ground and the top of the building. To increase the robustness of the linear regression, we use all the points that are on the same side of the building, a side being defined by a segment in the shapefile of the building footprint. Once this reference height is computed, it is converted into the reference phase using the InSAR acquisition metadata. Then, it can be subtracted from the measure InSAR phase to analyze the phase residue. The phase residue can either be due to deformation or from a discrepancy between this reference phase and the scatterers phase center. To compensate the latest, the reference height is updated by estimating the height offset from the conversion of the InSAR phase residue to height for acquisition close to the reference image, and acquisition in the same month but different years. This choice is motivated by the results of [Weissgerber2017] that showed that in this dataset, the deformations were mainly due to thermal expansion and thus were very small between acquisitions one year apart, for which temperatures are close. Having compensated the reference height for the difference between LiDAR height and the phase center height, the observed deformation patterns are mostly linear with the façade elevation, aligned with deformation due to thermal expansion. A more in-depth analysis has to be carried out to detect small phase anomalies that could indicate non-homogenous thermal deformation or deformation from another origin. Moreover, the difference between the height and the phase center height could also be analyzed either to understand the scattering mechanism of these buildings façades or to update the 3D representation of buildings by details captured only in the InSAR phase. References [Weissgerber2017] Flora Weissgerber, Elise Colin-Koeniguer, Jean-Marie Nicolas et Nicolas Trouvé, “3D Monitoring of Buildings Using TerraSAR-X InSAR, DInSAR and PolSAR Capacities”, Remote Sens. 2017, 9(10), 1010; doi:10.3390/rs9101010 [Weissgerber2022] Flora Weissgerber, Laurane Charrier, Cyril Thomas , Jean-Marie Nicolas and Emmanuel Trouvé (2022) LabSAR, a one-GCP coregistration tool for SAR–InSAR local analysis in high-mountain regions. Front. Remote Sens. 3:935137. doi: 10.3389/frsen.2022.93513
Resolution enhancement of polarimetric images using a high resolution mono-channel image
No full textInternational audiencePolarimetric SAR images provide information about the scattering mechanisms that increases the capacity of urban areas analysis. However, due to technological constraint, their resolution is often coarser than the resolution of single channel SAR images. To overcome this, we propose a resolution enhancement algorithm for polarimetric images using a mono-channel SAR image acquired in interferometric condition. This algorithm is based on the spectral properties of point-like scatterers. It is tested on airborne and spaceborne data. The point-like scatterers are well focused and their polarimetric and interferometric behaviours are preserved
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