1,720,962 research outputs found
Building profile reconstruction using TerraSAR-X data time-series and tomographic techniques
Get PDFThis work aims to show the potentialities of SAR Tomography (TomoSAR) techniques for the 3-D characterization (height, reflectivity, time stability) of built-up areas using data acquired by the satellite sensor TerraSAR-X. For this purpose 19 TerraSAR-X single-polarimetric multibaseline images acquired over Paris urban area have been processed applying classical nonparametric (Beamforming and Capon) and parametric (MUSIC) spectral estimation techniques
Fast terrain modelling for hydrogeological risk mapping and emergency management: the contribution of high-resolution satellite SAR imagery
No full textGeomatic tools fast terrain modelling play a relevant role in hydrogeological risk mapping and emergency management. Given their complete independence from logistic constraints on the ground (as for airborne data collection), illumination (daylight), and weather (clouds) conditions, synthetic aperture radar (SAR) satellite systems may provide important contributions in terms of digital surface models (DSMs) and digital elevation models (DEMs).For this work we focused on the potential of high-resolution SAR satellite imagery for DSM generation using an interferometric (InSAR) technique and using a revitalized radargrammetric stereomapping approach. The goal of this work was just methodological. Our goal was to illustrate both the fundamental advantages and drawbacks of the radargrammetric approach with respect to the InSAR technique for DSM generation, and to outline their possible joint role in hydrogeological risk mapping and emergency management. Here, it is worth mentioning that radargrammetry procedures are independent of image coherence (unlike the interferometric approach) and phase unwrapping, as well as of parsimony (only a few images are necessary). Therefore, a short time is required for image collection (from tens of minutes to a few hours), thanks to the independence from illumination and weather. The most relevant obstacles of the technique are speckle and the lack of texture impact on image matching, as well as the well-known deformations of SAR imagery (layover and foreshortening), which may produce remarkable difficulties with complex morphologies and that must be accounted for during acquisition planning.Here, we discuss results obtained with InSAR and radargrammetry applied to a COSMO-SkyMed SpotLight triplet (two stereopairs suited for radargrammetry and InSAR, sharing one common image) acquired over suburbs of San Francisco (United States), which are characterized by mixed morphology and land cover. We mainly focused on urban areas and zones covered by bare soil and rocks. Image processing was performed using the well-known commercial software SARscape® for InSAR, and the radargrammetric suite implemented in SISAR, software developed at the Geodesy and Geomatic Division of the University of Rome "La Sapienza".Global accuracies were approximately 5 m using both approaches. However, several differences in terrain morphology reconstruction were determined and are underlined and evaluated here, as well as a possible way to further enhance the results using the integration of InSAR and radargrammetry. © 2014 © 2014 Taylor & Francis
Evaluation and comparison of different radargrammetric approaches for Digital Surface Models generation from COSMO-SkyMed, TerraSAR-X, RADARSAT-2 imagery: Analysis of Beauport (Canada) test site
No full textIn this manuscript we analyze the potentialities of the radargrammetric DSMs generation using high resolution SAR imagery acquired by three different platforms (COSMO-SkyMed, TerraSAR-X and RADARSAT-2), with particular attention to geometric orientation models. Two orientation models are considered and compared: Toutin's model (Canada Center for Remote Sensing), implemented in the commercial software package PCI-Geomatica and based on Ground Control Points (GCPs), and the radargrammetric model implemented in the scientific software SISAR (University of Rome La Sapienza), based on images metadata orbital information only. Moreover, a comparison between the DSMs following the image matching approaches implemented in PCI-Geomatica and SISAR has been performed. The analysis has been carried out over Beauport test site (Quebec, Canada), where three overlapping stereopairs, one for each of the mentioned platform, were acquired and a LiDAR ground truth and a dense set of GNSS Check points (CPs) are available. The presented results appear promising: DSMs accuracy are within 4 and 5 m for all sensors, independently from orientation model (with or without GCP) and image matching approach, provided good relative orientation is guaranteed, what mainly attains to the quality of metadata orbital information. (C) 2014 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS)
Fast terrain modeling for hydrogeological risk mapping and emergency management: the contribution of high resolution satellite SAR imagery
No full textGeomatic tools for fast terrain modelling play a relevant role both for hydrogeological risk mapping and for hydrogeological emergency management. Among these tools, Synthetic Aperture Radar (SAR) satellite systems may give important contributions in terms of Digital Surface Models (DSMs) and Digital Elevation Models (DEMs), considering their complete independence from logistic constraints on the ground (as for airborne data collection), illumination (daylight) and weather (clouds) conditions. Here we focus on the present potentialities of high resolution SAR satellite imagery for DSMs generation with the radargrammetric stereo-mapping approach and with the well-known interferometric technique. Therefore, the goal of this paper is just methodological, devoted to illustrate both the fundamental advantages of radargrammetric approach and also its drawbacks respect to the InSAR technique. As regards the pros, it is worth to mention the independence from image coherence (unlike interferometric approach), the parsimony (it can work with just a couple of images), and therefore the short time required for imagery collection (from tens of minutes to few hours) also thanks to the mentioned independence from illumination and weather. Concerning the cons, the well known deformations of SAR imagery (layover and foreshortening) may cause remarkable difficulties with complex morphologies and have to be duly accounted for the acquisition planning. A suite for the DSMs generation through the radargrammetric approach has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at the Geodesy and Geomatic Division of the University of Rome La Sapienza. In order to demonstrate the radargrammetric mapping potentialities of high resolution SAR satellite imagery, several tests were carried out using data with different features (SpotLight, StripMap) coming from different platforms (COSMO-SkyMed, TerraSAR-X). Here we discuss the results obtained with a COSMO-SkyMed SpotLight stereo-pairs related to the San Francisco area, which is characterized by mixed morphology and land cover; we mainly focused on urban areas and zones covered by bare soil and rocks. Overall, accuracies range from 3 m over bare soil to about 4 m over more complex morphology, whereas they decrease in presence of remarkable image deformations
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
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