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ABSTRACT: To provide the data needed for testing sonar signal processing
schemes, it is desirable to simulate the sonar environment and the
received signals. The paper gives a description of a simulator developed
for this purpose. The simulator runs on a personal computer, which makes
it an attractive alternative to more expensive machines, both for system
evaluation and for training purposes. It consists of two parts, the
environmental part (consisting of the target, reverberation and
propagation models) and the system part (providing appropriate signal
processing functions). The simulator employs a novel target echo model
IEE Proceedings - Radar Sonar and Navigation 09/1997; · 0.55 Impact Factor
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ABSTRACT: The effects of a flat sea surface on the secondary wave field for
a parametric acoustic source with a piston type transmit transducer have
been assessed both theoretically and experimentally. When the virtual
array of a parametric source is truncated by the sea surface, the
amplitude of the secondary signal is reduced. In addition to the normal
cancellation between the direct and surface reflection paths, there are
two more mechanisms which cause the reduction of the signal level with a
rough sea surface. The first one is the destructive summation of the
secondary field before and after the intersection with the surface, the
second one is the loss of the coherence of the primary signals after
reflection. The Westervelt model is used to predict the secondary field.
Experiments in an indoor laboratory tank have been carried out to
measure the primary and secondary fields. It is found that, with a flat
water surface, the reduction in the signal level depends on the
characteristics of the parametric source and the geometry of the
problem. Both the theory and experiments show that there is a maximum
loss caused by the truncation. The experimental results indicate that
the maximum loss is almost 10 dB in signal level for the problem
concerned, while the theory predicts an even higher value
OCEANS '96. MTS/IEEE. 'Prospects for the 21st Century'. Conference Proceedings; 10/1996
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ABSTRACT: In target tracking with an active sonar, a major problem is the
association of new echoes with track data previously collected. This
paper reports work on a method for associating a sonar target's echoes
with an existing track by assigning a degree of association by means of
gates, the sizes of which are determined by a genetic algorithm using a
simulator. The resultant gates encapsulate the uncertainties and the
imperfections imposed by the system and the environment, and also are
able to take into account unexpected changes in the target's dynamic
behaviour. The results presented here illustrate the effective role of
the GA as a robust learner in this application
Genetic Algorithms in Engineering Systems: Innovations and Applications, 1995. GALESIA. First International Conference on (Conf. Publ. No. 414); 10/1995
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ABSTRACT: The paper addresses some reflection and scattering phenomena for a
model telemetry channel with a periodically fluctuating surface.
Limitations on the extent of surface fluctuations are derived from the
reflection and scattering area, Rayleigh parameter and shadow function.
These results are related to the observed pulsed response of the
surface. Finally the effect of the scattering process on communication
coherence is briefly discussed
OCEANS '94. 'Oceans Engineering for Today's Technology and Tomorrow's Preservation.' Proceedings; 10/1994
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ABSTRACT: Although a number of optical methods for bubble-sizing already
exist, e.g. photography and holography, they suffer from the
disadvantage that a number of time-consuming steps are involved between
taking the image and analysing it. Furthermore, exposure times and
shutter speeds are often a matter of trial and error, and the process of
analysing the results is tedious and therefore error-prone. The authors
propose a method which will allow in situ real-time measurements of the
spatial bubble size distribution of a bubble screen or cloud to be
performed. The method involves looking at fringes produced by laser
light scattered from individual bubbles. Although this technique has
been used before by Langley and Marston (l984), the present authors
propose employing spatial filters and an optical correlator to automate
the identification of bubble sizes. analysis shows that this method will
apply to bubbles with radii ranging from about 1O μm up to 1 mm or 2
mm, to an accuracy of a few per cent
Electronic Engineering in Oceanography, 1994., Sixth International Conference on; 08/1994
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ABSTRACT: The application of expert system principles as part of the signal processing chain for target detection in an active sonar system is being researched at the University of Birmingham. In order to establish the rules by which the expert system is to operate it is necessary to evaluate the characteristics of the sonar environment and the received signals. A convenient method of generating these is by using a software simulator. This paper reports on the progress made in the development of such a real-time simulator in which the problems to be tackled by the expert system are those of tracking the returns from a moving target against a background of reverberation and of producing a constant false alarm rate
Simulation Techniques Applied to Sonar, IEE Colloquium on; 06/1988
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ABSTRACT: Describes a real-time passive-sonar simulator. Most of the processing involved in the simulator is carried out in the frequency domain; the arguments for doing this are presented. The spectrum of noise radiated by a target vessel can be modelled as a frequency spectrum in which the spectral components are generated stochastically. Propagation effects are also modelled in the frequency domain. While it is possible to produce a model containing multiple paths where differential time delays and transmission losses are incorporated, it is more efficient to generate the propagation model stochastically. Similarly, the spectrum of the ambient noise is also generated stochastically. This noise spectrum is added in the frequency domain to the received signal spectrum and then an inverse Fourier transformation is made to generate a time waveform which models the output from a single hydrophone
Simulation Techniques Applied to Sonar, IEE Colloquium on; 06/1988
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ABSTRACT: A tunable sandwich transducer is reported which has its
fundamental resonant frequency controlled by varying a passive reactive
load. The structure consists of four PZT-4 rings sandwiched between an
aluminium head-mass and a brass tail-mass. The electromechanical
coupling coefficient and the radiation efficiency into water of the
transducer are given over the frequency range 25 to 75 kHz. A
theoretical analysis based on an electromechanical equivalent circuit
shows good agreement with the experimental results
Electronics Letters 04/1988; · 0.96 Impact Factor
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ABSTRACT: Details are given of an underwater transducer which is tunable over the frequency range 250 kHz to 700 kHz. The structure comprises a pair of 50 mm-diameter lead zirconate titanate ceramic plates suitably mounted. The resonant frequency of the structure is electronically controlled by varying in a predetermined manner the amplitude and phase of the voltage applied to one of the ceramics.
Electronics Letters 02/1986; · 0.96 Impact Factor
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ABSTRACT: The paper is a review of current design and constructional practice of conventional high-frequency transducers which make use of piezoelectric plates and discs. The main design technique is based on the concept of the equivalent circuit, and to emphasise the design techniques three contemporary designs of increasing sophistication are detailed. The problems likely to be encountered are discussed. Electrical data on these designs are included to illustrate the measurement techniques usually employed.
Communications, Radar and Signal Processing, IEE Proceedings F. 07/1984;
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ABSTRACT: The equivalent circuits for high-frequency transducers with quarter-wave matching layers, such as are used in sonar and ultrasonic applications, are discussed in terms of simple lumped bandpass filter circuits. Expressions for the matching criteria are given for half-section and full-section filters.
Electronics Letters 02/1979; · 0.96 Impact Factor
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ABSTRACT: The possibility of applying some random-signal radar proposals made by Poirier to a random-signal sonar is discussed A proposal for obtaining bearing information is presented, together with some experimental results. It appears that the limitations inherent in this type of random-signal system severely restrict the useful operation of a practical sonar.
Electronics Letters 02/1970; · 0.96 Impact Factor
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ABSTRACT: An experimental study of the interaction between cylindrically spreading acoustic waves in water is described, and experimental results are given. The experimental results are compared with theoretical work separately published by one of the authors.
Electronics Letters 10/1965; · 0.96 Impact Factor
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ABSTRACT: Westervelt and Bellin and Beyer have studied the scattering of intermodulation frequency sound waves arising from the nonlinear interaction of two collimated and coincident plane waves of sound of different frequencies. This work is extended to account for the finite aperture formed by the cross-section of the column; experimental results are compared with those obtained theoretically and with Bellin and Beyer's results.
Electronics Letters 04/1965; · 0.96 Impact Factor
