1,720,961 research outputs found
A robust change detection feature for Cosmo-SkyMed detected SAR images
No full textAutomated change analysis of multi-temporal SAR images is a challenging task due to the inherent noisiness of SAR imagery and the variability of the backscattering coefficient to the acquisition angle. Several methods have been proposed in the literature to improve the change detection performances with respect to the classical method based on the Log-Ratio operator. In this paper a pixel change feature is proposed and tested on true Cosmo-SkyMed detected images for damage assessment applications. The method does not require any despeckling pre-processing and is robust both to the acquisition noise and to possible variation of the acquisition angle in the two observations
Non-parametric change detection in multitemporal SAR images based on mean-shift clustering
No full textA nonparametric method for unsupervised change detection in multipass synthetic aperture radar (SAR) imagery is described. The method relies on a novel feature capturing the structural change between two SAR images and is robust to the statistical change that may be originated by speckle and coregistration inaccuracies. The proposed method starts from the scatterplot of the amplitude levels in the two images and applies the mean-shift (MS) algorithm to find the modes of the underlying bivariate distribution. If we assume that the two images are preliminarily coregistered and calibrated on one another, then all the modes lying outside the main diagonal correspond to the structural changes across the two observations. The value of the probability density function (PDF) in any of the off- diagonal modes found by the MS algorithm is translated into a value of conditional information. This value is assigned to all image pixels generating the corresponding cluster in the scatterplot. Thus, a feature is obtained on a per-pixel basis. Experimental results on simulated changes and true SAR images acquired by the COSMO-SkyMed satellite constellation show that the proposed feature exhibits significantly better discrimination capability than the classical log-ratio (LR). Advantages over a preliminary version of the method without MS regularization and over another nonparametric method based on Kullback-Leibler divergence are also demonstrated. The method is robust when it is applied to SAR images with different acquisition angles, whose effects are deemphasized compared to the actual scene changes
Performance of pansharpening methods varying with input data formats
No full textIn this work, we investigate on how the performance of pansharpening methods depends of their input data format, either floating-point, e.g. spectral radiance, or digital numbers (DN) in a packed fixed-point representation. It is theoretically proven and experimentally demonstrated that methods based on multiresolution analysis are unaffected by the data format, which instead is crucial for methods based on component-substitution (CS), unless the intensity component is calculated by means of a multivariate linear regression between the upsampled bands and the lowpass-filtered Pan, as it occurs for the most advanced CS methods. In an experimental setup, WorldView-2 data are either fused in their original 11-bits DN format, or converted to spectral radiance before fusion, by applying the gains and off sets provided in the file header. In the former case, fusion results are converted to spectral radiance before quality is measured. Nine fusion methods have been considered: results exactly match the theoretical investigations. For the majority of CS fusion methods, which do not feature a regression-based intensity calculation, results are better whenever they are obtained from floating-point calibrated data
Screening of Spotlight CSK images for large area monitoring and detection of infrastructures
No full textThis paper presents an automatic pre-screening algorithm of SAR images of huge size (more than 20;000x20;000 pixels), which is capable to identifying extended infrastructures in an effective and computationally efficient way. The algorithm is tested on true one-look Cosmo-SkyMed SAR image data for target detection purposes on an airport scenario. Both visual and objective results are presented to show the potentials of the proposed method
Robust unsupervised nonparametric change detection of SAR images
No full textThis paper presents an unsupervised nonparametric method for change detection in multitemporal synthetic aperture radar (SAR) imagery. The proposed method relies on a novel feature capable of capturing the structural changes between the two images and discarding almost completely the statistical changes due to speckle patterns or co-registration inaccuracies. This feature utilizes the scatterplots of the amplitude levels in the two SAR images and applies a fast version of the mean-shift (MS) algorithm to find the modes of the underlying bivariate distribution. The value of the probability density function (PDF) is translated to a value of conditional information and given to all image pixels originating such modes. Experimental results have been carried out with simulated changes and true SAR images acquired by the COSMO-SkyMed satellite constellation. The proposed feature exhibits significantly better discrimination capability than both the classical log-ratio (LR) and is particularly robust if applied to SAR images having different processing and/or acquisition angles
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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