Multibeam Sonar Theory of Operation

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Sonar Concepts Multibeam Sonar Theory of Operation Clearly, this is highly advantageous. Multibeam sonars can map complete swaths of the bottom in roughly the time it takes for the echo to return from the farthest angle. For a 120°-swath system, this time is twice the ping cycle time of a single-beam sounder, but such a system typically provides over 100 soundings as opposed to only one. Because they are far more complex, the cost of a multibeam sonar can be many times that of a single-beam sonar. However, this cost is more than compensated by the savings associated with reduced ship operating time. As a consequence, multibeam sonars are the survey instrument of choice in most mapping applications, particularly in deep ocean environments where ship operating time is expensive. The SEA BEAM 2100 is a multibeam sonar system. It maps up to 151 sounding points at 1° intervals with each ping, and can cover areas tens of kilometers wide in depths of a few kilometers. How this is accomplished is the subject of the rest of this document. Page 2-14 Copyright © 2000 L-3 Communications SeaBeam Instruments No portion of this document may be reproduced without the expressed written permission of L-3 Communications SeaBeam Instruments
Introduction to Multibeam Sonar: Multibeam Sonar Theory of Operation Projector and Hydrophone Systems Chapter 3 - Introduction to Multibeam Sonar: Projector and Hydrophone Systems The previous chapter examined how multibeam sonar can be used to make up for many of the short comings of single-beam sonar. It introduced the concept of directivity and narrow projector beams. This chapter describes how • groups of projectors, called projector arrays, and groups of hydrophones, called hydrophone arrays, can be used to produce narrow transmit and receive beams, a process called beam forming • these narrow beams can be targeted at specific angles using beam steering processes • a hydrophone array can be used to simultaneously record sound from many steered beams • projector and hydrophone arrays are combined in a Mills Cross arrangement • all of these techniques are employed in the SEA BEAM 2100 system Projector Arrays and Beam Forming Recall from the section, “A Single-Beam Depth Sounder,” in Chapter 2, that a ping from a simple single-beam echo sounder expands spherically with uniform amplitude as it propagates through water, spreading its acoustic energy equally in all directions. This symmetric spreading is called an isotropic expansion, and the projector that produces it is called an isotropic source. A good example of a wave with isotropic expansion is the circular pattern produced when a small stone is dropped in a quiet pond (see Figure Chapter 3 - -1). Copyright © 2000 L-3 Communications SeaBeam Instruments Page 3-1 No portion of this document may be reproduced without the expressed written permission of L-3 Communications SeaBeam Instruments
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