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Editorial. Biologically-inspired radar and sonar systems
No full textIn the last century both radar and sonar active technology developed from inception to the point where high resolution images can be obtained from long ranges. The available technology can exploit Doppler effects, structural resonances, nonlinear scattering, synthetic aperture platforms, and sediment-penetrating modalities. Active sonar and radar share many common approaches, in part because of the similarities of the problems they address, both in the military and commercial research areas. Moreover, in the last two decades, research into both radar and sonar has explored biomimetic and bioinspired solutions, in recognition of the fact that whilst man-made systems have access to power and bandwidth far beyond that available to any living organism, some biological solutions have benefitted from millions of years of natural optimisation to evolve sensing capabilities and strategies and meet the challenges of survival (finding food and mates, avoiding predators, sensing and navigating to and within appropriate habitats, etc.). Problem solving for survival goes beyond the particular radiation used in sensing, covering also signal processing, detection and classification of targets, use of platforms, and strategies for deploying sensors and interpreting data. Bio-inspired approaches follow logically when the problems facing manufactured technology resemble those addressed in nature. For example, in the last 15 years the arena for sonar challenge has changed from the passive detection of large quiet nuclear submarines in the deep, relatively quiet and uncluttered waters, to minehunting by active sonar in shallow coastal waters, a problem far closer to that faced by dolphins and bats in their natural environments
Passive radar detection of drones with staring illuminators of opportunity
No full textPassive Bistatic Radars (PBRs) use non-cooperative illuminators of opportunity to
detect, localise and track targets. They have attracted considerable research interest
in recent years because they can be operated and deployed at a relatively low cost,
are difficult to detect and hence allow covert operations in hostile environments
and do not require the allocation of an increasingly more congested frequency
spectrum. Various analogue and digital communication systems (such as television
(TV) and radio broadcast systems) have been studied and exploited as illuminators
of opportunity. However, despite the extensive work carried out on PBRs that
exploit random communication signals, there has been limited research investigating
the use of existing non-cooperative radar systems as illuminators of opportunity.
The exploitation of radar signals to achieve passive bistatic detection is
attracting attention as it may offer significant advantages. Because common radar
waveforms are deterministic, a reference channel is essentially not required to
detect a target. Prior intelligence or live estimations of the deterministic waveform
design parameters allow the passive receiver to be matched with the illuminator of
opportunity and thus generate a range–Doppler map. Radar signals are also
designed for detection and provide Doppler tolerance, large bandwidths (which
provide good range resolutions) and good compression ratios.
This chapter presents a PBR solution that exploits non-random signals transmitted
by a non-cooperative staring radar system to detect drones. Staring radars
offer a constant illumination of the volume under surveillance and, unlike radar
systems that deploy a rotating antenna, offers a continuous signal of opportunity.
They are very attractive illuminators in particular for short-range applications to
detect low Radar Cross Section (RCS) and slow moving targets
Bistatic radar signature of buried landmines
Get PDFWith the proliferation of low-intensity conflict, landmines have proven to be one of the weapons of choice for both government and guerrilla forces around the world. Recent improvements to mine technology pose increasingly significant problems for demining operations, requiring the constant upgrading of countermine technologies. Ground Penetrating Radar (GPR) is one of the most exhaustively researched topics in the detection of buried mines as it can be used to detect non-metallic and plastic mines. However, identification and recognition are still unsolved problems, due to the scattering similarity between mines and clutter objects. This study provides an experimental evaluation of the improvements that a bistatic approach could yield and what can be gained from investigating the angular dependencies of the landmine radar signature
Characterization of the internal structure of landmines using ground penetrating radar
Get PDFOne of the principal limitations of employing Ground Penetrating Radar (GPR) for landmine detection is the presence of clutter, i.e. reflections from the surrounding environment which might interfere with the landmine echoes. Clutter presents similar scattering characteristics of typical targets and may significantly raise the detection threshold of the system. A capability to characterise the internal structure of a buried target might provide key unique information to develop advanced landmine-clutter discrimination algorithms, considering that the presence of internal scattering components can be univocally associated to man-made targets. In this paper, the possibility of identifying and characterising these contributions from the GPR signature of a landmine is numerically assessed and experimentally validated. The simulated response from a landmine-like target shows that the presence of the internal structure generates additional reflection peaks, as a consequence of the layered structure of the object, and the field trials corroborate that it is possible to identify these scattering components and delineate their spatial distribution
Exploitation of deterministic signals for passive single-channel detection
No full textPassive Bistatic Radar (PBR) systems use noncooperative illuminators of opportunity to detect, localise and track targets. The aim of this paper is to investigate the potential of PBR target detection in the presence of non-random signals emitted by non-cooperative transmitters of opportunity, such as radar systems, and without the use of a reference channel. An experiment to detect a moving target was carried out at the Defence Academy of the United Kingdom to demonstrate target detection capabilities using a low cost off-the-shelf receiver. Results show that moving targets can be successfully detected although care must be taken in correcting for frequency offset effects deriving from the non-coherency and non-stability of the receiver local oscillator
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
Passive detection using a staring radar illuminator of opportunity
No full textThis paper presents results of an experimental trial aimed at detecting a car and a flying drone, passively, by exploiting transmissions of opportunity from a staring Holographic radar. Results show that targets could be successfully detected using a low-cost passive receiver prototype. This may be considered a first step towards a radar network that could provide more comprehensive coverage, over a wider area, against a broader set of target types and without requiring additional spectral resources
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