Browsing by Author "Griffiths, Hugh D."

Now showing 1 - 12 of 12
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    Biomimetic echolocation with application to radar and sonar sensing
    (IEEE , 2014-03-25T00:00:00Z) Baker, Chris J.; Smith, Graeme E.; Balleri, Alessio; Holderied, Marc W.; Griffiths, Hugh D.
    Nature provides a number of examples where acoustic echolocation is the primary sensing modality, the most well-known of these being the bat, whale and dolphin. All demonstrate a remarkable ability to "see with sound". Using echolocation they navigate, locate and capture prey. As species, they have not only survived but have thrived in all their individual environments, often solely reliant on echolocation. All of these creatures are inherently cognitive. They all maintain a perception of their environment through the nervous system that allows them to take actions. In this paper we focus on the bat as an example of a cognitive system exploiting a memory-driven perception-action cycle, enabling it to navigate and interact with its environment. The key conceptual components of cognition and how it could be applied to man-made echoic sensors is introduced. This is followed by a description of how echoic flow fields, a bio-inspired technique that bats have been shown to use, fit guidance and control problems. We then go on to explain how bats are able to reliably distinguish between different targets. A combination of the theory and examples is used to demonstrate the vast potential for advancing the capability of made in man-made systems by adopting aspects of natural echolocating cognitive dynamic systems.
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    Bistatic radar signature of buried landmines
    (Institution of Engineering and Technology (IET), 2017-10) Lombardi, Federico; Griffiths, Hugh D.; Balleri, Alessio
    With 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.
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    Characterization of the internal structure of landmines using ground penetrating radar
    (IEEE, 2020-02-13) Lombardi, Federico; Griffiths, Hugh D.; Lualdi, Maurizio; Balleri, Alessio
    One 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.
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    Dependence of landmine radar signature on aspect angle
    (Institution of Engineering and Technology (IET), 2017-02-06) Lombardi, Federico; Griffiths, Hugh D.; Wright, Lauren; Balleri, Alessio
    Antipersonnel landmines have been indiscriminately used since World War II, and their longterm persistence in the ground creates a barrier to development in a large number of countries, forcing people to live in constant fear. Therefore, there is a growing demand for reliable landmine inspection systems that could achieve an exhaustive detection to and return the land to its normal use. Due to its ability of detecting both metallic and non-metallic objects, Ground Penetrating Radar (GPR) has successfully been demonstrated to be a meaningful method for detecting landmines, allowing faster and safer operations. Most landmines may be considered as multiple layered dielectric cylinders, which each interface causes a reflection, properties that are hardly expected in other commonly encountered clutter objects. Considering that these features have their own angular pattern and will respond differently to different illumination, landmines are expected to produce signatures that present some discriminant features that could be used for reducing the false alarm rate of GPR equipment. In this paper, a set of measurements of three inert landmines has been acquired to study and characterise landmine signatures as a function of the antenna orientation relative to the landmine and target aspect angle.
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    Experimental analysis of multistatic multiband radar signatures of wind turbines
    (Institution of Engineering and Technology (IET), 2016-05-23) Balleri, Alessio; Fioranelli, Francesco; Ritchie, Matthew; Griffiths, Hugh D.
    This study presents the analysis of recent experimental data acquired using two radar systems at S-band and X-band to measure simultaneous monostatic and bistatic signatures of operational wind turbines near Shrivenham, UK. Bistatic and multistatic radars are a potential approach to mitigate the adverse effects of wind farm clutter on the performance of radar systems, which is a well-known problem for air traffic control and air defence radar. This analysis compares the simultaneous monostatic and bistatic micro-Doppler signatures of two operational turbines and investigates the key differences at bistatic angles up to 23°. The variations of the signature with different polarisations, namely vertical transmitted and vertical received and horizontal transmitted and horizontal received, are also discussed.
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    Experimental analysis of multistatic wind turbine radar clutter statistics
    (Institution of Engineering and Technology (IET), 2023-02-01) Fioranelli, Francesco; Ritchie, Matthew; Balleri, Alessio; Griffiths, Hugh D.
    This Letter presents preliminary results of the analysis of amplitude statistics of wind turbine clutter as extracted from multistatic radar data. It is shown that the T-location-scale distribution provides good fitting of the experimental data, and that there are combinations of bistatic angle and polarisations where the bistatic clutter has more favourable statistics for target detection than the simultaneous monostatic clutter.
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    Landmine internal structure detection from ground penetrating radar images
    (IEEE, 2018-06-11) Lombardi, Federico; Griffiths, Hugh D.; Balleri, Alessio
    Reliable landmine detection is still an unresolved problem. Demining operations are complex activities because of the large variety of existing landmine types, many different possible soil and terrain conditions, and environmental circumstances. Due to its ability of detecting both metallic and non-metallic objects, ground penetrating radar (GPR) is a promising method for detecting landmines that may allow faster and safer operations. As the performance of GPR is mainly governed by the target signature, the potential of discriminating target based on the presence of internal reflections could be a valuable advantage for identification and recognition process. This study demonstrates that from a set of high resolution GPR slices the internal design of the landmine can be properly imaged and characterised, confirming the applicability of the methodology and the validity of such an approach.
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    Practical investigation of multiband mono- and bistatic radar signatures of wind turbines
    (Institution of Engineering and Technology (IET), 2017-03-17) Fioranelli, Francesco; Ritchie, Matthew; Balleri, Alessio; Griffiths, Hugh D.
    The negative effects wind farm clutter has on the performance of radar systems for Air Traffic Control and Air Surveillance is well-known in the radar research community and several mitigation techniques have been proposed to address this problem. These include bistatic and multistatic radar systems providing multiple views of the area under surveillance, and hence potential additional information that can be used to improve the receiver performance. This paper presents the analysis of a set of experimental data collected simultaneously by two radar systems, one operating at S-band and one at X-band, of echoes from an operational wind farm in the UK near Oxford. This analysis presents several parameters extracted from the time domain data and the Doppler spectra, such as Doppler centroid and bandwidth of the micro-Doppler signature as well as amplitude statistics of the time domain returns. These parameters are characterised using data recorded at monostatic and bistatic nodes, as well as at different polarisation combinations.
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    Preliminary results on multi offset GPR for imaging of landmines
    (IEEE, 2017-07-31) Lombardi, Federico; Griffiths, Hugh D.; Balleri, Alessio; Lualdi, Maurizio
    Ground Penetrating Radar (GPR) is widely recognised as an operationally useful sensor for mine detection as it can offer better detection performance than the ubiquitous metal detector in the presence of low-metal content mines. However, GPR has to overcome many potential sources of false alarm due to clutter and battlefield debris, which lower the efficiency of the sensor. This paper analyses a set of experimental data collected in a recent multi-offset GPR measurement campaign with inert landmines composed of different assemblies buried in sandy soil. The aim of the work is to evaluate the key differences observed by a radar system when the transmitter and the receiver are moved apart, as a function of their distance and hence when the illuminated section of the target is diversified. The results of the comparison between the collected multi-offset profiles show that using a bistatic geometry could represent a strategy to reconstruct composite objects with finer and better details.
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    The radar signature of the Wind Lens: a less disruptive wind turbine?
    (2013-08-25T00:00:00Z) Balleri, Alessio; Al-Armaghany, A.; Griffiths, Hugh D.; Tong, Kenneth; Matsuura, Takashi
    We study the radar signature of a new type of wind turbine, named the Wind Lens. This design includes a flanged shroud around the turbine which concentrates the wind flow past the turbine blades and hence improves the efficiency. The design also offers improved safety, and reduces acoustic noise. Furthermore, it may offer a significantly lower radar signature, which may make the design much more attractive for use in situations where conventional wind turbine designs may disturb the operation of radars. We present the results of an experimental trial, carried out in the UK, to measure the Radar Cross Section (RCS) of a 5 kW Wind Lens turbine prototype and we provide a reference database that can be used for comparing the Wind Lens RCS with that of conventional turbines. We investigate methods to further reduce the Wind Lens RCS and present the results of a time-varying Doppler analysis. Results show that the addition of a metallic mesh around the shroud obscures the rotating blades, and hence mitigates the RCS by 15 dBm2, at angles where the radar interference is highest.
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    RSN editorial 2024
    (Institution of Engineering and Technology (IET), 2024-01-05) Griffiths, Hugh D.; Balleri, Alessio
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    Sensing, cognition, and engineering application [Further Thoughts]
    (IEEE , 2014-03-25T00:00:00Z) Baker, Chris J.; Smith, Graeme E.; Balleri, Alessio; Holderied, Marc W.; Griffiths, Hugh D.
    Definitions of cognition almost always use the term “knowing.” Sensors probe the environment producing stimuli that are interpreted to form a perception, but “knowing” is something that takes place within the brain of a human after being presented with sensed data or some form of image. Consider radar and air traffic control. A radar sensor scans the airspace and, using the principles of echolocation, is able to detect, locate, and display aircraft on a screen. An air traffic controller views the screen and continually repositions the aircraft using strict protocols that comply with safety of life requirements. In other words, it is the air traffic controller who supplies the cognitive component necessary to achieve air safety.