Page 401 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

394 CHAPTER 15 Sonar
FIGURE 15.6
Directional beam
30 dB
20 10
Omnidirectional beam
Directivity index for a circular as well as a directional sound beam.
FIGURE 15.7
Target 2
Actual beam
As depicted on sonar screen
Target 1
Target in the side lobe of this beam will produce an echo at the receiver.
a by-product of this main lobe, side lobes, develop that are also subject to backscatter off secondary tar- gets. An analogy to this concept is the simple push of the hand on the surface of a swimming pool, direct- ing a wave pulse in a specific direction. As the hand is pushed in one direction, it can be noticed that the main pulse pushes in the direction of the wave but side waves emanate on either side of the main wave.
15.1.7 Active sonar
The majority of civilian sonar systems falls under the classification of active sonar. Active sonar systems make use of beam forming, frequency shifting, and backscatter analysis to characterize