Multibeam Sonar Theory of Operation

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Multibeam Sonar Theory of Operation Detection Processing and Range Calculations In Figure Chapter 4 - -4, a time t 1 has passed since the sonar system has transmitted a ping. As yet, the ping has not reached the bottom, so there are no bottom echoes produced at time t 1 . The time slice at time 2 × t 1 , which is when any echoes produced at time t 1 would be received (remember, any echoes must travel back to the hydrophone array, and to do so requires the same amount of time it took the ping to propagate outward) will contain no echoes from the sea floor. However, it will have measurable amplitudes, as pictured in Figure Chapter 4 - -5. These amplitudes are due to background noise (discussed in “The Principles of Sonar” in Chapter 2). Figure Chapter 4 - -4: Hydrophone Array at Time t1 Figure Chapter 4 - -5: Time Slice at Time 2 · t 1 Copyright © 2000 L-3 Communications SeaBeam Instruments Page 4-7 No portion of this document may be reproduced without the expressed written permission of L-3 Communications SeaBeam Instruments
Detection Processing and Range Calculations Multibeam Sonar Theory of Operation Figure Chapter 4 - -6 considers the same hydrophone array at a later time t 2 . The ping has propagated to the point where it is intersecting the bottom at a single point, at angle θ A to the hydrophone array. The time slice at time 2 × t 2 contains the echo from this point (see Figure Chapter 4 - -7). Note that θ A does not necessarily occur at one of the axes of the steered beams— in general it will occur at angles between two beams. The echo will cause high amplitudes in several surrounding beams— strongest in those closest, but measurable in others. This is because each steered beam has a beamwidth (as discussed in the section, “Projector Arrays and Beam Forming,” in Chapter 3). For instance, the beam with axis at θ 7 in Figure Chapter 4 - -7, receives the echo at θ A close to its axis— near the peak response of the beam— so it generates a strong amplitude. The beam with axis θ 9 receives the same echo farther away from its axis, generating a weaker amplitude. Far away beams, such as those at θ 2 and θ 12 , do not see the echo at all. Figure Chapter 4 - -6: Hydrophone Array at Time t2 Page 4-8 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
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Multibeam Sonar Theory of Operation

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