Multibeam Sonar Theory of Operation
Multibeam Sonar Theory of Operation
Multibeam Sonar Theory of Operation
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Introduction to <strong>Multibeam</strong> <strong>Sonar</strong>:<br />
<strong>Multibeam</strong> <strong>Sonar</strong> <strong>Theory</strong> <strong>of</strong> <strong>Operation</strong> Projector and Hydrophone Systems<br />
Hydrophone Arrays<br />
The previous section described how arrays <strong>of</strong> projectors can be used to generate narrow beams<br />
<strong>of</strong> sound that will ensonify small patches <strong>of</strong> the sea floor. Hydrophones as well as projectors can<br />
be formed into arrays. Where projector arrays transmit sound into narrow beams, hydrophones<br />
arrays are used to receive sound from narrow beams.<br />
It is easy to see how this works. In Figure Chapter 3 - -9 through Figure Chapter 3 - -14, a line<br />
array <strong>of</strong> hydrophones is examined in two situations. In Figure Chapter 3 - -9, a source<br />
perpendicular to the axis <strong>of</strong> the line array is producing sound waves. The source <strong>of</strong> these sound<br />
waves is in the far field, such that the wave fronts striking the hydrophone array are a series <strong>of</strong><br />
parallel lines. Each hydrophone in the array is making an independent measurement <strong>of</strong> the wave.<br />
The signal measured by each hydrophone as a function <strong>of</strong> time can be plotted in what is called a<br />
signal trace. Figure Chapter 3 - -10 shows signal traces for three <strong>of</strong> the hydrophones. Because<br />
the parallel waves are striking these hydrophones at exactly the same time, these three plots are<br />
identical— measured peaks and troughs occur at the same times. The three measurements are<br />
said to be in phase. Summing the three hydrophone traces results in a trace with the same<br />
frequency but three times the amplitude (pictured in Figure Chapter 3 - -11)— the measurements<br />
<strong>of</strong> the three hydrophones add constructively. Collectively, the hydrophone array is highly sensitive<br />
to sounds from this direction.<br />
Figure Chapter 3 - -9: Hydrophone Array with a Perpendicular Source<br />
Copyright © 2000 L-3 Communications SeaBeam Instruments Page 3-11<br />
No portion <strong>of</strong> this document may be reproduced without the expressed written permission <strong>of</strong> L-3 Communications SeaBeam Instruments