1,720,973 research outputs found
ISAR Imaging via Compressive Sensing
No full textThis paper aims at giving an overall view of the use of Compressive Sensing (CS) for some applications of Inverse Synthetic Aperture Radar (ISAR) imaging, especially for those where conventional Fourier based approaches typically fail. A number of case studies have been investigated in this paper and CS algorithm’s performances have been numerically evaluated via the definition of image contrast
Propagation Effects on HF Skywave MIMO Radar
No full textMIMO technology has been suggested as an eective tool to overcome some of the
issues typical of conventional OTH skywave radars. The advantages of the application
of MIMO technology to HF Skywave radars is based on the transmission
of multiple linearly independent waveforms and their separation at the receiver.
Notwithstanding, the high instability of the ionosphere is responsible for severe
signal fading and degradation that can prevent the separation with consequences
on the radar performance. The present thesis is concerned with the problem of
the eects of ionospheric propagation, which are analyzed from a theoretical point
of view at rst, through the description of the ionosphere morphology and the
disturbances that aect the ionospheric electron density structure. The relation
between structural variations in the ionosphere and the transmitted signal parameters
has been then derived. A radar signal simulator has been realized accordingly
to the signal model proposed in the thesis. The results of the thesis concern three
dierent aspects of propagation in HF MIMO radars. The orthogonality of the
transmitted waveforms after ionospheric propagation is analyzed rst, while the
eects of ionospheric propagation on the results of conventional beamforming is
studied secondly. The performance of the radar receiver are evaluated in terms of
ROCs in case of multipath propagation and compared to the single path case
Super resolution ISAR imaging via Compressive Sensing
No full textDeveloping compressed sensing (CS) theory has been applied in radar imaging by exploiting the inherent sparsity of radar signal. In this paper, we develop a super resolution (SR) algorithm for formatting inverse synthetic aperture radar (ISAR) image with limited pulses. Assuming that the target scattering field follows an identical Laplace probability distribution, the approach converts the SR imaging into a sparsity-driven optimization in Bayesian statistics sense. We also show that improved performance is achieved by taking advantage of the meaningful spatial structure of the scattering field. To well discriminate scattering centers from noise, we use the non-identical Laplace distribution with small scale on signal components and large on noise. A local maximum likelihood estimator combining with bandwidth extrapolation technique is developed to estimate the statistical parameters. Experimental results present advantages of the proposal over conventional imaging methods
Super resolution ISAR imaging via Compressing Sensing
No full textInverse Synthetic Aperture Radar (ISAR) is a well known technique which provides high-resolution radar images of moving targets. To obtain effective ISAR images, spatial resolutions should be small enough with respect to the target size. However, due to the bandwidth and Coherent Processing Interval (CPI) limitation achieving high enough spatial resolutions is a challenging task for existing radar imaging systems. This motivates the need for Super Resolution (SR) techniques. In this paper, a two-dimensional Compressive Sensing (CS) algorithm is investigated for the reconstruction of an ISAR image with enhanced spatial resolutions and tested on real data
Compressive sensing-based inverse synthetic radar imaging imaging from incomplete data
No full textThe applicability of compressive sensing (CS) to radar imaging has been recently proven and its capability to construct reliable radar images from a limited set of measurements demonstrated. In this study, a common framework for inverse synthetic aperture radar (ISAR) imaging via CS is provided and a CS-based ISAR imaging method is proposed. The proposed method is tested for application such as image reconstruction from compressed data, resolution enhancement and image reconstruction from gapped data. The effectiveness of the proposed method is demonstrated on real datasets and the performance evaluated by means of image contrast
Propagation effects on high frequency skywave multiple-input--multiple-output radar
No full textAbstract:
Multiple-input–multiple-output (MIMO) technology has been suggested as an effective tool in overcoming some
of the issues that are typically relate to conventional over the horizon radars. Notwithstanding, effects, such as fading and multipath propagations are ever present and cannot be avoided even when using a MIMO configuration. For this reason, a study on the impact of such effects on high frequency (HF) skywave MIMO radars is fundamental for an effective design of such systems. This study aims to study the effects of ionos pheric propagation on the performance of the HF MIMO skywave radar. In particular, the relationship between the transmitted signal parameters and the ionospheric variations because of perturbations is highlighted in a suitable signal model. The performance analysis is performed in terms of estimated direction of arrival and loss of virtual array elements
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
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