Underwater Acoustic Reflection from Surfaces and Shapes

Underwater Acoustic Reflection from Surfaces and Shapes
Author: Werner G. Neubauer
Publisher:
Total Pages: 408
Release: 1986
Genre: Science
ISBN: 9780932146328

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Acoustic Reflection from Surfaces and Shapes is a magnificent collection of mini-studies of underwater acoustic reflection and scattering, theoretical and experimental, from varied shapes and surfaces. These studies were carried out by the Acoustics Division at the Naval Research Laboratory during the period from 1958 through 1978 under the leadership of Dr. Werner G. Neubauer, with the assistance and guidance of Dr. Louis R Dragonette. The driving force for this research, of course, addressed the improvement of understanding of sound interacting with submarine targets with the ultimate goal being to improve detection of submarines by submarine and surface ship sonars. Accordingly, the varied shape and surface targets addressed in the studies were related to those of a submarine or sections thereof: cylinders, spheres, spheroids, ellipsoids and flat surfaces. The book has 23 chapters, each a different study. Depending on the purpose of an individual study, the shapes and surfaces addressed were made of various materials; possessed various degrees of elasticity and rigidity; and had various internal volumes, from completely solid to various degrees of internal space. Echo reduction effectiveness of reflection-reduction coatings and absorbing and non-absorbing surfaces was also measured. And the forecited surface and shape targets were "painted" by steady state or transient acoustic signals as determined by the purpose of each individual study. The seminal studies in this book can provide underwater acousticians and modelers with valuable qualitative and quantitative insights on the reflected signals, reverberation and noise returned from submarines that will eventually lead to feeding the sonar equation.

An Experiment on Acoustic Reflection from the Sea Surface

An Experiment on Acoustic Reflection from the Sea Surface
Author: Raymond H. Ferris
Publisher:
Total Pages: 18
Release: 1970
Genre:
ISBN:

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An experiment on underwater acoustic relfection from the ocean's surface was conducted in a water depth of 32 m by utilizing an omnidirectional, 3.5-kHz fixed source at a submerged depth of 16 m. Two-cycle pulses at a repetition rate of 10 pulses per second were received on a hydrophone suspended at a depth of 10.7 m from a small boat. Underwater grazing angles ranged from 15 to 40 degrees. Surface reflection loss was observed to vary over a range of approximately 20 dB with periods closely associated with the predominant water wave periods. Surface reflection gains of up to 5 dB occurred frequently. The average loss ranged from 1 dB at a grazing angle of 15 degrees to 4 dB at an angle of 40 degrees, with only a slight dependence on direction of propagation relative to the direction of the sea. Signals propagated via the surface-reflected path, when correlated with signals propagated via the direct path, exhibited an average peak value of normalized cross correlation of 0.95. (Author).

Acoustic Reflection from a Plane Boundary Having Variable Surface Parameters

Acoustic Reflection from a Plane Boundary Having Variable Surface Parameters
Author:
Publisher:
Total Pages: 19
Release: 1991
Genre:
ISBN:

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A possible technique for studying the acoustic reflection from continuous plane surfaces such as flat plates covered with thin anechoic coatings is discussed. It is particularly directed to complex coatings which include a regular array of non-homogeneous inclusions within their structures. The method involves the experimental determination of a position-dependent quantity which can be viewed as either a surface transfer admittance or a surface transfer mobility function. This function can then be used in a mathematical convolution procedure to determine the nature of the reflected wave from the surface when it is ensonified by an incident uniform plane wave arriving in a direction normal to the plate surface. The basic theory behind the proposed method is presented for a surface having a periodic, two-dimensional spatial variation. As a side issue, this approach raises a question as to the applicability of an 'average surface admittance' approach used previously to estimate reflection coefficients of Alberich coatings. The basic elements of an experimental system for measuring the surface admittance functions are discussed.