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David S. Burnett
Postal:
Naval Surface Warfare Center, Panama City, FL 32407 USA
Email:
david.s.burnett@navy.mil
Computer Simulation for Predicting Acoustic Scattering from Objects at the Bottom
of the Ocean
Applying the modern discipline of computational mechanics to solving complex mathematical problems in acoustics.
Introduction
Since the early 20th century, SONAR (SOund Navigation And Ranging) has been used in military, commercial and scientific applications to help find objects sub- merged in the oceans, either by listening passively with underwater hydrophones to the sounds that noisy objects emit (passive sonar) or by actively projecting sound into the water and listening to the echoes reflected from quiet objects (active so-
Figure 1 An underwater scenario depicting a sonar wave (red arrow) insonifying various objects on or near the sedimentary ocean bottom – rock, mine, concrete pipe, fish school – and the resulting sound waves scattered back from the objects (pink arrows).
nar, Figure 1). Sonar has been used successfully for detection (is there something out there?), localization (where is it?), some degree of classification (what type of object is it, e.g., man-made or marine organism?) and some degree of iden- tification (what is the object?). In order to more precisely identify the nature of a detected object, an active sonar technique has recently emerged that produces additional information about the object, including not only its size and shape but also its internal composition. The resulting body of information is referred to as the “acoustic scattering signature” (Burnett, 2015), or just acoustic signature, of the object.
28 | Acoustics Today | Winter 2015, volume 11, issue 1 ©2015 Acoustical Society of America. All rights reserved.