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Author: Publisher: ISBN: Category : Languages : en Pages : 35
Book Description
The goal of this project was to complete a study of Bahar's full-wave approach to rough surface scattering that was begun under ONR support. The two proposed items of technical work have been fully completed. In the ONR-supported work, a study was begun for a simplified scattering problem: Scattering from a one-dimensional (1-D) surface with the Dirichlet (zero field) boundary condition using a Gaussian roughness spectrum. The full-wave method was implemented numerically and used in Monte Carlo calculations of the scattering cross section. Comparisons were then made with exact integral equation results, and with the Kirchholl and perturbation approximations. It was found that the full- wave prediction did not reduce to the lowest order perturbation prediction when the perturbation result was known to be accurate, as shown by exact calculations. This is contrary to conclusions reached by Bahar and is an important finding, showing that the full-wave approach is not as general as previously thought. The full-wave prediction did reduce to the Kirchhoff prediction when the Kirchhoff approximation is known to be accurate, as shown by exact calculations. In fact, the full-wave result was found to agree closely with the Kirchhoff result for all cases studied, whether or not the Kirchhoff result was accurate. (rrh).
Author: Publisher: ISBN: Category : Languages : en Pages : 35
Book Description
The goal of this project was to complete a study of Bahar's full-wave approach to rough surface scattering that was begun under ONR support. The two proposed items of technical work have been fully completed. In the ONR-supported work, a study was begun for a simplified scattering problem: Scattering from a one-dimensional (1-D) surface with the Dirichlet (zero field) boundary condition using a Gaussian roughness spectrum. The full-wave method was implemented numerically and used in Monte Carlo calculations of the scattering cross section. Comparisons were then made with exact integral equation results, and with the Kirchholl and perturbation approximations. It was found that the full- wave prediction did not reduce to the lowest order perturbation prediction when the perturbation result was known to be accurate, as shown by exact calculations. This is contrary to conclusions reached by Bahar and is an important finding, showing that the full-wave approach is not as general as previously thought. The full-wave prediction did reduce to the Kirchhoff prediction when the Kirchhoff approximation is known to be accurate, as shown by exact calculations. In fact, the full-wave result was found to agree closely with the Kirchhoff result for all cases studied, whether or not the Kirchhoff result was accurate. (rrh).
Author: Anthony A. Triolo Publisher: ISBN: Category : Scattering (Physics) Languages : en Pages : 222
Book Description
Rough surface scattering is a current topic of interest in many diverse fields. But, despite its importance, the two most widely used solution methods, the Kirchhoff and first order perturbation methods, are valid only for a restricted range of surface types. There is a large range of surface statistics for which neither of these theories is valid. There are purely numerical solutions to the problem, i.e., the integral equation technique and FDTD method, but these methods require a prohibitively large amount of computer time and storage space for use in practical applications. A full wave method has been introduced by E. Bahar which agrees with the Kirchhoff method in its range of validity, but does not bridge the gap between the later two standard theories and does not provide understanding of the physical processes involved in rough surface scattering. Consequently, it has been a center of controversy since modifications made to improve the method seem arbitrary and are without mathematical or physical justification. The method presented here is a new full wave method which uses equivalent currents to provide insight into the physical scattering processes. This full wave method analytically reduces to the two standard theories in their respective regions of validity and bridges the gap between the two, which was shown by comparison to the integral equation method. The results presented here are for statistically rough surfaces with Gaussian distributed heights and slopes. A Monte Carlo procedure is used to generate the radar cross section data for this new full wave method.
Author: F. G. Bass Publisher: Elsevier ISBN: 1483187756 Category : Science Languages : en Pages : 541
Book Description
Wave Scattering from Statistically Rough Surfaces discusses the complications in radio physics and hydro-acoustics in relation to wave transmission under settings seen in nature. Some of the topics that are covered include radar and sonar, the effect of variations in topographic relief or ocean waves on the transmission of radio and sound waves, the reproduction of radio waves from the lower layers of the ionosphere, and the oscillations of signals within the earth-ionosphere waveguide. The book begins with some fundamental idea of wave transmission theory and the theory of random processes as used to rough surfaces and to wave fields. This discussion is followed by an analysis of the average fields of sound and electromagnetic waves. A section on spatial correlation characteristics in the approximation of small perturbations is then given. Another chapter of the text explains the Kirchhoff method. The book will provide useful information to physicists, mechanical engineer, students, and researchers in the field of acoustics.
Author: E. R. Pike Publisher: Elsevier ISBN: 0080540732 Category : Science Languages : en Pages : 1831
Book Description
Scattering is the collision of two objects that results in a change of trajectory and energy. For example, in particle physics, such as electrons, photons, or neutrons are "scattered off" of a target specimen, resulting in a different energy and direction. In the field of electromagnetism, scattering is the random diffusion of electromagnetic radiation from air masses is an aid in the long-range sending of radio signals over geographic obstacles such as mountains. This type of scattering, applied to the field of acoustics, is the spreading of sound in many directions due to irregularities in the transmission medium. Volume I of Scattering will be devoted to basic theoretical ideas, approximation methods, numerical techniques and mathematical modeling. Volume II will be concerned with basic experimental techniques, technological practices, and comparisons with relevant theoretical work including seismology, medical applications, meteorological phenomena and astronomy. This reference will be used by researchers and graduate students in physics, applied physics, biophysics, chemical physics, medical physics, acoustics, geosciences, optics, mathematics, and engineering. This is the first encyclopedic-range work on the topic of scattering theory in quantum mechanics, elastodynamics, acoustics, and electromagnetics. It serves as a comprehensive interdisciplinary presentation of scattering and inverse scattering theory and applications in a wide range of scientific fields, with an emphasis, and details, up-to-date developments. Scattering also places an emphasis on the problems that are still in active current research. The first interdisciplinary reference source on scattering to gather all world expertise in this technique Covers the major aspects of scattering in a common language, helping to widening the knowledge of researchers across disciplines The list of editors, associate editors and contributors reads like an international Who's Who in the interdisciplinary field of scattering
Author: J. A. Ogilvy Publisher: CRC Press ISBN: Category : Art Languages : en Pages : 300
Book Description
A review of theories developed for the study of acoustic, elastic and electromagnetic wave scattering from randomly rough surfaces, and a comprehensive summary of the latest techniques. Different theories are illustrated by experimental data.With applications in radar, sonar, ultrasonics and optics this book will be invaluable to graduate students, researchers and engineers.
Author: Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
This report summarizes the principal results in three areas of investigation. The first is a new full wave method that takes two dimensional surface roughness into account and does not use the telegraphist's equations. The second study concerns scattering from a rough surface when the incident field is a gaussian beam. The third is a summary of the difficulties inherent in Bahar's extended full wave theory on which the prediction of enhanced backscatter was based. It was found that enhanced backscatter occurred only because of the invalid assumption that the heights and slopes were uncorrelated.
Author: Leung Tsang Publisher: John Wiley & Sons ISBN: 0471463795 Category : Technology & Engineering Languages : en Pages : 432
Book Description
A timely and authoritative guide to the state of the art of wave scattering Scattering of Electromagnetic Waves offers in three volumes a complete and up-to-date treatment of wave scattering by random discrete scatterers and rough surfaces. Written by leading scientists who have made important contributions to wave scattering over three decades, this new work explains the principles, methods, and applications of this rapidly expanding, interdisciplinary field. It covers both introductory and advanced material and provides students and researchers in remote sensing as well as imaging, optics, and electromagnetic theory with a one-stop reference to a wealth of current research results. Plus, Scattering of Electromagnetic Waves contains detailed discussions of both analytical and numerical methods, including cutting-edge techniques for the recovery of earth/land parametric information. The three volumes are entitled respectively Theories and Applications, Numerical Simulation, and Advanced Topics. In the third volume, Advanced Topics, Leung Tsang (University of Washington) and Jin Au Kong (MIT), cover: * Two-dimensional random rough surface scattering * Kirchhoff and related methods for rough surface scattering * Analytic theory of volume scattering based on cascading of layers * Analytic wave theory for medium with permittivity fluctuations * Multiple scattering theory for discrete scatterers * Quasicrystalline approximation in dense media scattering * Dense media scattering * Backscattering enhancement
Author: Publisher: ISBN: Category : Languages : en Pages : 13
Book Description
This final report summarizes work done under Grant DAAHO4-94- g-0035. The objective of the investigation was to develop a more rigorous full wave approach to rough surface scattering than that used by Bahar in his full wave method Instead of relying on the use of telegraphists equations a local spectral expansion method was found that is applicable to general rough surface scattering, not just surfaces with roughness in one dimension only. The local spectral expansion method can be formulated so as to involve the tangential fields at the surface as the only unknowns. This is in contrast with Bahar's full wave method which involves coupling integrals between the modes used in expanding the field and is more difficult to use in an iterative procedure. The new method turns out, in the lowest approximation involving the Kirchhoff approximation for the surface tangential fields, to yield significantly more accurate results for most scattering angles. The new approach also covers a wider range of surface parameters that extend from the small perturbation regime to the standard Kirchhoff regime.
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Author: Anthony A. Triolo
Author: F. G. Bass
Author: E. R. Pike
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Author: J. A. Ogilvy
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Author: Leung Tsang
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