摘要:

The paper starts with a review of sidescan imagery and the history of sidescan sonar and continues with the acoustic and technical factors affecting the sonar design for any specified application. There follows a description of present-day applications in the civilian field, and the paper ends with discussion of possible future developments.

DOI:10.1049/ip-f-1.1984.0041

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A brief introduction is given to the functions of detection and classification of underwater objects by sonars which scan large volumes of water. For classification purposes the system must have high angular resolution in at least one plane, and this, coupled with high-speed scanning to cover the width of a sector within the time duration of the transmit pulse, typifies what is called ‘within-pulse scanning’. A brief description of the general theory of high-speed scanning by electronic means leads to practical methods for their implementation followed by some details of systems developed and used for various purposes. In addition to the scanning receivers, this includes other parts essential to the systems, such as transmitters, transducers, stabilisation and display. Some limitations of the water medium are mentioned before the various applications of within-pulse sector-scanning sonar to fisheries research are described.

DOI:10.1049/ip-f-1.1984.0042

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Despite the advantage of high average power output, traditional continuous transmission FM (CTFM) sonars suffer from two major defects: separate transmit and receive transducers are required, and the demodulated signal is unavailable for a proportion of the sweep period. The paper shows how, by using a dual-demodulation system, the demodulated signal can be made continuous, resulting in the complete elimination of the blind time and in a range resolution as good as two wavelengths of the mean frequency. Experimental results using a CTFM air sonar justify both these claims.

DOI:10.1049/ip-f-1.1984.0043

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The paper discusses the finite-element modelling and performance of ring-shell projectors, a particular type of flextensional projector. A ring-shell projector can be used near its resonance frequency as a high-power source, or as a moderate-power broadband source. The most recent design of ring-shell projector has a resonance frequency of 349 Hz, a mechanicalQ-factor of 10.6 and a source level of 205 dB relative to 1 μPa at 1 m. Finite-element predictions of the transmitting response and admittance show good agreement with the measured values. Ring-shell projectors that are passively pressure compensated have a maximum operating depth in excess of 300 m and a safe immersion depth of at least 450 m.

DOI:10.1049/ip-f-1.1984.0044

出版商:IEE    

年代:1984

数据来源: IET

摘要:

This paper describes the evolution of a 10.5 kHz sandwich element, developed to suit a cylindrical transducer array. It is essentially a guide to the practical problems encountered in designing sandwich elements, and the equations used are very much simplified. The approach is somewhat empirical, the eventual design being reached after differing prototype elements had been constructed; however, even with a more exact analysis it is unlikely that the need for prototype elements can be dispensed with.

DOI:10.1049/ip-f-1.1984.0045

出版商:IEE    

年代:1984

数据来源: IET

摘要:

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.

DOI:10.1049/ip-f-1.1984.0046

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A theoretical treatment of the response of a towed array to the acoustic field from a point source in isovelocity shallow water is presented. The analysis, which is based on a wave-theoretical representation of the field, reveals several interesting effects when the source is endfire-on to the array. Beam broadening or beam splitting may occur due to the distribution of the modal energy in elevation, a feature which also leads to signal rejection by the array. The latter phenomenon is characterised by a signal gain which, in general is less than the directivity index of the array. Other aspects of performance which are addressed include the effects of range averaging, the dependence of the output on the source-depth/receiver-depth combination, and the noise gain of the system when the limit to the signal/noise ratio is set by wind-generated ambient noise.

DOI:10.1049/ip-f-1.1984.0047

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The problem of echo fading and the inherent time- and frequency-diversity reception provided by coherent processing is discussed, leading to a description of an experimental investigation into the shallow-water performance of a coherent processor. A statistical analysis of the results clearly demonstrates the benefits of coherent processing in reducing the effects of echo fading and providing a significant improvement in the probability of detection of a target sphere compared with that provided by a simple energy detector system of equivalent bandwidth and, hence, nominally equivalent reverberation-limited performance.

DOI:10.1049/ip-f-1.1984.0048

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Traditional speed measuring devices have been largely replaced by the acoustic Doppler log. This can make measurements of velocity relative to the sea bed, but only in modest operating depths. Greater depths can be attained using the correlation log. This is not yet an established technique, and the principles of the design parameters for a satisfactory system are discussed.

DOI:10.1049/ip-f-1.1984.0049

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The input/output relationship describing a given signal-processing application in its entirety can be partitioned into a set of primitive operations which may be represented using signal-processing graph notation (SPGN) as a network of interconnected processes. A set of alternate low-level primitive structures (ALPS) can be defined to implement the operations underpinning each node in this network. This SPGN/ALPS processor network is queue driven and message based, each queue consisting of a message header and an array of data. Current systems developments have demonstrated that a small, finite set of low-level primitives is sufficient for the synthesis of the majority of acoustic-processing problems, and the paper outlines the design approach for some of these. In particular, a prime-radix DFT algorithm, FIR and IIR filter structures using constrained filter coefficients and a general purpose array address mapping element are described. In addition, system architectures based on these SPGN/ALPS networks are developed.

DOI:10.1049/ip-f-1.1984.0050

出版商:IEE    

年代:1984

数据来源: IET