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Author: Derek Olson Publisher: ISBN: Category : Languages : en Pages :
Book Description
This research is concerned with acoustic scattering from rough, elastic interfaces. The primary results of this dissertation consist of acoustic scattering measurements coupled with environmental characterization. Acoustic data from a sea trial in April 2011 that took place in the Oslofjord, Norway near Larvik were used to estimate the scattering cross section, and probability of false alarm. The data were obtained from high-frequency, high-resolution interferometric synthetic aperture sonar system. Since the acoustic system has not been calibrated, an effective calibration of this sonar was performed based on a natural feature with estimated roughness and a valid scattering model. The seafloor around Larvik, Norway consists of glacially-eroded outcrops of rock, which possesses both very rough and very smooth roughness characteristics. These outcrops have been characterized in terms of their elastic properties based on previously measured mineral composition. Their roughness characteristics were measured during the a field experiment conducted in May 2013. A stereo photogrammetry system was designed and built for the purpose of obtaining high resolution roughness measurements. These height field measurements are used to form power spectrum estimates, which were used calibrate the acoustic system. Statistical characterization of facet sizes and orientations were used to motivate numerical modeling.For the very rough areas on the rock outcrops, no analytic approximate scattering model is valid. Connections between surface parameters, and trends in the scattering cross section and probability of false alarm were made using the boundary element method. Surface roughness measurements were used to motivate several surface generation methods that approximate a glacially quarried rough surface. Through numerical parametric studies, hypotheses for the relationship between the scattered field and rough interface were established.
Author: Derek Olson Publisher: ISBN: Category : Languages : en Pages :
Book Description
This research is concerned with acoustic scattering from rough, elastic interfaces. The primary results of this dissertation consist of acoustic scattering measurements coupled with environmental characterization. Acoustic data from a sea trial in April 2011 that took place in the Oslofjord, Norway near Larvik were used to estimate the scattering cross section, and probability of false alarm. The data were obtained from high-frequency, high-resolution interferometric synthetic aperture sonar system. Since the acoustic system has not been calibrated, an effective calibration of this sonar was performed based on a natural feature with estimated roughness and a valid scattering model. The seafloor around Larvik, Norway consists of glacially-eroded outcrops of rock, which possesses both very rough and very smooth roughness characteristics. These outcrops have been characterized in terms of their elastic properties based on previously measured mineral composition. Their roughness characteristics were measured during the a field experiment conducted in May 2013. A stereo photogrammetry system was designed and built for the purpose of obtaining high resolution roughness measurements. These height field measurements are used to form power spectrum estimates, which were used calibrate the acoustic system. Statistical characterization of facet sizes and orientations were used to motivate numerical modeling.For the very rough areas on the rock outcrops, no analytic approximate scattering model is valid. Connections between surface parameters, and trends in the scattering cross section and probability of false alarm were made using the boundary element method. Surface roughness measurements were used to motivate several surface generation methods that approximate a glacially quarried rough surface. Through numerical parametric studies, hypotheses for the relationship between the scattered field and rough interface were established.
Author: Allan D. Pierce Publisher: Academic Press ISBN: 1483257703 Category : Science Languages : en Pages : 340
Book Description
High Frequency and Pulse Scattering investigates high frequency and pulse scattering, with emphasis on the phenomenon of echoes from objects. Geometrical and catastrophe optics methods in scattering are discussed, along with the scattering of sound pulses and the ringing of target resonances. Caustics and associated diffraction catastrophes are also examined. Comprised of two chapters, this volume begins with a detailed account of geometrically based approximation methods in scattering theory, focusing on waves transmitted through fluid and elastic scatterers and glory scattering; surface ray representations of scattering by shells and other smooth objects; and caustics and associated diffraction catastrophes. The second chapter deals with the relation between sound pulses and the vibrational spectra of elastic submerged objects. The theory of the scattering of sound pulses from elastic and impenetrable objects is described, together with the theory of surface wave pulses. Target resonances and the singularity expansion method are also analyzed. This book will be of interest to physicists.
Author: Susan K. Numrich Publisher: ISBN: Category : Languages : en Pages : 21
Book Description
Measurements have been made of sound scattered in the specular direction by fixed rough surfaces. The surfaces used were physical realizations of computer generated topographies which corresponded to Gaussian distributions in height to within specified limits. Measurements were made in water using 0.5-, 1.0-, and 2.25-MHz transducers. Transient pulse analysis techniques were used to provide information about the scattered pulse over a wide range of frequencies. Comparisons are made with several theoretical models including a multiple scattering model. The scattered field is also illustrated by means of schlieren visualization. (Author).
Author: Publisher: ISBN: Category : Languages : en Pages : 47
Book Description
Research in the following areas is reported: (A) Scattering of high- frequency sound by elastic objects in water--Experiments and theory are examined mostly for problems not describable by thin shell theory including: backwards- wave high-frequency enhancement of backscattering by shells; coincidence frequency enhancement for chirped bursts and impulses; a novel impulse generator and the effect of the mass-per-area of the shell on the specular return; and the application of time-frequency analysis. Some leaky wave scattering properties are examined including the Fresnel width of the coupling region, a convolution formulation, and a variable phase coupling coefficient. Retro-reflective backscattering of sound due to Rayleigh waves on objects with corners is demonstrated. (B) Radiation mechanisms for fluid-loaded plates--A flexural wavepacket is launched to propagate down a plate that has only its bottom half submerged. When the packet crosses the free surface of the water, there is a burst of acoustic radiation into the water due to the jump in fluid loading. This transition radiation is measured and modeled. (C) Caustic wavefields and diffraction catastrophes--Echo fluctuations associated with caustics in wavefields produced by reflection from rough surfaces and optical observations of E6 diffraction catastrophes. (D) Interaction of sound with sound mediated by a suspension.
Author: Allan D. Pierce Publisher: Academic Press ISBN: 1483257762 Category : Technology & Engineering Languages : en Pages : 395
Book Description
Underwater Scattering and Radiation describes the relevant theoretical foundations of underwater scattering and radiation. Acoustic scattering from elastic solids is discussed, and variational formulations in acoustic radiation and scattering are presented. Surface waves and quasi-cylindrical modes are also explored, along with the Helmholtz-Kirchhoff integral corollaries. Comprised of two chapters, this volume begins with a comprehensive account of scattering by elastic objects, focusing on the classic idealized shapes of spheres and infinite cylinders. The reader is introduced to important concepts such as normal modes, the S-matrix, and the T-matrix as well as resonances, whispering gallery modes, Franz modes, and Stoneley waves. Subsequent sections describe methods for treating scattering by elastic bodies of more general shapes. The T-matrix formalism is discussed and then applied to spheroidal scatterers and finite cylinders. The second chapter analyzes how variational principles can be used in acoustics, with the choice of topics directed toward applications to underwater acoustic radiation and scattering. This book will be of interest to physicists.
Author: Darrell Jackson Publisher: Springer Science & Business Media ISBN: 0387369457 Category : Science Languages : en Pages : 634
Book Description
This book is a research monograph on high-Frequency Seafloor Acoustics. It is the first book in a new series sponsored by the Office of Naval Research on the latest research in underwater acoustics. It provides a critical evaluation of the data and models pertaining to high-frequency acoustic interaction with the seafloor, which will be of interest to researchers in underwater acoustics and to developers of sonars. Models and data are presented so as to be readily usable, backed up by extensive explanation. Much of the data is new, and the discussion in on two levels: concise descriptions in the main text backed up by extensive technical appendices.
Author: Dieter Guicking Publisher: World Scientific ISBN: 9814497819 Category : Science Languages : en Pages : 443
Book Description
The interaction of acoustic fields with submerged elastic structures, both by propagation and scattering, is being investigated at various institutions and laboratories world-wide with ever-increasing sophistication of experiments and analysis. This book offers a collection of contributions from these research centers that represent the present state-of-the-art in the study of acoustic elastic interaction, being on the cutting edge of these investigations. This includes the description of acoustic scattering from submerged elastic objects and shells by the Resonance Scattering Theory of Flax, Dragonette and Überall, and the interaction of these phenomena in terms of interface waves. It also includes the use of this theory for the purpose of inverse scattering, i.e. the determination of the scattered objects properties from the received acoustic backscattered signals. The problem of acoustically excited waves in inhomogeneous and anisotropic materials, and of inhomogeneous propagating waves is considered. Vibrations and resonances of elastic shells, including shells with various kinds of internal attachments, are analyzed. Acoustic scattering experiments are described in the time domain, and on the basis of the Wigner-Ville distribution. Acoustic propagation in the water column over elastic boundaries is studied experimentally both in laboratory tanks, and in the field, and is analyzed theoretically. Ultrasonic nondestructive testing, including such aspects like probe modelling, scattering by various types of cracks, receiving probes and calibration by a side-drilled hole is also studied in details.A comprehensive picture of these complex phenomena and other aspects is presented in the book by researchers that are experts in each of these domains, giving up-to-date accounts of the field in all these aspects.
Author: Derek Olson
Author: Derek Olson
Author: Raymond Harvey Owen
Author: Allan D. Pierce
Author: Robert Peter Banaugh
Author: Susan K. Numrich
Author: 
Author: Allan D. Pierce
Author: Vijay K. Varadan
Author: Darrell Jackson
Author: Dieter Guicking