Download e-book for kindle: Fisheries Acoustics: Theory and Practice (Fish and Aquatic by John Simmonds, David MacLennan

By John Simmonds, David MacLennan

Dwelling assets of the ocean and clean water have lengthy been an enormous resource of foodstuff and monetary job. With fish shares carrying on with to be over-exploited, there's a transparent specialise in fisheries administration, to which acoustic tools can and do make a major contribution. the second one variation of this standard ebook covers the numerous technological advancements that have happened because the first version; hugely subtle sonar and laptop processing apparatus provide nice new possibilities and Fisheries Acoustic, 2e offers the reader with a greater figuring out of ways to interpret acoustic observations and placed them to sensible use. popular and revered authorsEmphasis on sensible acoustic methodsDetailed insurance of a commercially and environmentally vital topic an essential software for fisheries scientists, fisheries oceanographers, environmental biologists, ecologists, inhabitants biologists, fish biologists, and marine biologists. All these concerned with layout and use of acoustic gear. Libraries in examine institutions, govt stations and universities the place fisheries technology is studied or taught will locate this a welcome boost to their cabinets.

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Sample text

There are other ways of describing the beam pattern by one parameter, such as the Directivity Index (Urick 1983) which expresses Underwater Sound 33 the difference between the actual beam pattern of the transducer and that of an omni-directional receiver. However, for most fisheries applications, we consider the EBA to be the most useful measure of transducer directivity. 2 Controlling the beam shape We have already described how a number of similar elements may be combined to determine the beam pattern of the complete transducer.

The limited experimental work published confirms that when using source levels of more than 222 dB//1 μPa at 1 m, and frequencies at or above 200 kHz, non-linear effects can be important. When echointegrating at high frequencies and power levels, it is preferable to calibrate with the sphere at greater ranges than those determined on near-field criteria alone (see below and Chapter 3). 8 provides guidance on the frequency/power limits above which non-linear distortions might be expected. Further details of the physics and applications of non-linear acoustics are given in Hamilton and Blackstock (1997).

This has several advantages compared to the conventional uniform type of piezo-electric material used in sonar transducers. Composites have a higher acoustic efficiency and a wider bandwidth. They also reduce the cross-talk (interference) between the elements, thus the beam patterns of composite transducers can be more accurately predicted. The transducers described by Foote (1998a) typically have between 5 and 10 dB change in sensitivity over the octave bandwidth. A transducer that is used to listen to underwater sound, like a microphone in air, is called a hydrophone.

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Fisheries Acoustics: Theory and Practice (Fish and Aquatic Resources) by John Simmonds, David MacLennan

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