1,721,031 research outputs found
Generalized-Capon method for Diff-Tomo SAR analyses of decorrelating scatterers
Full text linkIn synthetic aperture radar (SAR) remote sensing, Differential Tomography (Diff-Tomo) is developing as a powerful crossing of the mature Differential SAR Interferometry and the emerged 3D SAR Tomography. Diff-Tomo produces advanced 4D (3D+Time) SAR imaging capabilities, extensively applied to urban deformation monitoring. More recently, it has been shown that, through Diff-Tomo, identifying temporal spectra of multiple height-distributed decorrelating scatterers, the important decorrelation-robust forest Tomography functionality is possible. To loosen application constraints of the related main experimented full model-based processing, and develop other functionalities, this work presents an adaptive, just semi-parametric, generalized-Capon Diff-Tomo method, first conceived at University of Pisa in 2013, for joint extraction of height and dynamical information of natural distributed (volumetric) scatterers, with its formalization and a series of insights. Particular reference is given to the important functionality of the separation of different decorrelation mechanisms in forest layers. Representative simulated and P-band forest data sample results are also shown. The new Diff-Tomo method is getting a flexible and rich decorrelation-robust Tomography functionality, and is able to profile height-varying temporal decorrelation, for significantly distributed scatterers
On the Issue of Short-Term Decorrelation in Forest Tomography with Companion SARS
No full textIn the framework of developments of 3D forest SAR Tomography (Tomo-SAR), the issue of extensive and detailed characterizations of temporal decorrelation phenomena has emerged, especially for the future spaceborne operations. However, investigation has not been covered by ESA campaigns of height-varying characteristics of decorrelation processes acting at the short-term (fractions of second) scale, for the common case of volumetric scatterers complexly moving in windblown forests.In this work, a methodology is reported for new analyses of 4D Differential Tomography type of forest temporal decorrelation phenomena, exploiting a ground-based miniradar array with very quick acquisition capabilities. Moreover, corresponding recent real data results are presented, developing characterizations of both height- and time-varying behaviours of the short-term decorrelation in a representative experiment for a stand of trees in Italy (PisaScat experiment), in two different wind conditions and seasons.Consequently, indications are obtained that short-term decorrelation processes can affect also advanced spaceborne Tomo-SAR systems based on tandem (i.e. formation-flying) configurations, depending on the satellite time-lag, and their related products.This still unprecedented characterization concept and the new findings can be useful for current Tomo-SAR and also Pol-InSAR analyses, and most importantly, for development of the advanced mission concepts and programs of SAOCOM-CS-like kind, including LuTan-1
Improved Coherent Processing of Synthetic Aperture Radar Data through Speckle Whitening of Single-Look Complex Images
No full textIn this study, we investigate the usefulness of the spectral whitening procedure, devised by one of the authors as a preprocessing stage of envelope-detected single-look synthetic aperture radar (SAR) images, in application contexts where phase information is relevant. In the first experiment, each of the raw datasets of an interferometric pair of COSMO-SkyMed images, representing industrial buildings amidst vegetated areas, was individually (1) synthesized by the SAR processor without Fourier-domain Hamming windowing; (2) synthesized with Hamming windowing, used to improve the focalization of targets, with the drawback of spatially correlating speckle; and (3) processed for the whitening of complex speckle, using the data obtained in (2). The interferograms were produced in the three cases, and interferometric coherence and phase maps were calculated through 3 × 3 boxcar filtering. In (1), coherence is low on vegetation; the presence of high sidelobes in the system’s point-spread function (PSF) causes the spread of areas featuring high backscattering. In (2), point targets and buildings are better defined, thanks to the sidelobe suppression achieved by the frequency windowing, but the background coherence is abnormally increased because of the spatial correlation introduced by the Hamming window. Case (3) is the most favorable because the whitening operation results in low coherence in vegetation and high coherence in buildings, where the effects of windowing are preserved. An analysis of the phase map reveals that (3) is likely to be facilitated also in terms of unwrapping. Results are presented on a TerraSAR-X/TanDEM-X (TSX-TDX) image pair by processing the interferograms of original and whitened data using a non-local filter. The main results are as follows: (1) with autocorrelated speckle, the estimation error of coherence may attain 16% and inversely depends on the heterogeneity of the scene; and (2) the cleanness and accuracy of the phase are increased by the preliminary whitening stage, as witnessed by the number of residues, reduced by 24%. Benefits are also expected not only for differential InSAR (DInSAR) but also for any coherent analysis and processing carried out performed on SLC data
Psoriatic arthritis with spinal involvement in a patient receiving alpha-interferon for chronic hepatitis C.
No full textA 26-year-old male patient being treated with alpha-interferon for chronic hepatitis C developed psoriasis, seronegative oligoarthritis and sacroiliitis after four months. The close temporal relationship between the alpha-interferon therapy and the onset of skin and articular lesions strongly suggests that the drug played a role in the induction of the disease despite the absence of HLA antigens related to psoriatic arthritis. We cannot exclude the possibility that immunological alterations associated with HCV infection could have constituted a predisposing factor in the onset of the disease
Reduction of the phase-unwrapping drawbacks by a three antenna interferometric SAR system
No full textOne of the most critical steps of SAR interferometry for elevation mapping is the phase-unwrapping procedure. This paper analyzes the reduction of the phase-unwrapping drawbacks obtainable by using a recently proposed three-antenna SAR interferometer and a statistically optimal processor to estimate directly the interferometric phase with reduced ambiguity. A simulation of realistic scenarios is carried out. The performance analysis shows that the new technique significantly outperforms the conventional one, especially for high-relief terrains
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
- …
