Under the subject grant titled "Numerical Study of Rough Surface Scattering" research was conducted on rough surface scattering using an exact numerical method based on solving an integral equation. Boundary conditions appropriate to both sea surface and sea bottom scattering were employed. Numerical studies were used to examine the accuracy of approximations used with scattering theory, and various scattering phenomena were examined directly with numerical simulations and modeling. One important highlight from this work is that numerical simulations were used to show that roughness at the water/sediment interface could lead to significant acoustic penetration into sediment at incident grazing angles below the critical angle. This work played an important part in the development of the High Frequency Sediment Acoustics DRI which began in FY98. As part of the preparation for the DRI program, I chaired an ONR DRI Workshop in Monterosso, Italy, in July 1997.

This final technical report summarizes the results of work performed between 1 Sep 89 and 31 Mar 97 or accomplishments achieved as a result of this work. Finite-Difference Time-Domain code was developed for rough surface scattering. The phase perturbation, small slope approximation, local parabolic approximation, and nonlocal small slope approximation models for rough surface scattering were developed and examined for a number of different spectra and surface types.

The goal of this project was to improve our understanding of electromagnetic scattering from conducting rough surfaces when the roughness is small in comparison with the radiation wavelength. Research was conducted in two related areas for p-polarized scattering from conducting surfaces: the generation of surface waves, and the development of renormalized perturbation theory for scattering from perfectly conducting surfaces. To understand the excitation of surface waves better, a numerical method was developed for displaying the field near the surface; surface waves can then be shown explicitly. The method is based on integral equation solutions, and no fundamental approximations are required. The existence of surface waves for p-polarized scattering leads to difficulties in theoretical treatments of scattering from conductors. This work is specialized to the case of scattering from perfect conductors, for which the theoretical problems are most evident. A renormalized perturbation theory is implemented that is free from the deficiencies inherent in standard perturbation theory. The renormalized perturbation theory is extended beyond lowest order, and comparisons with exact integral equation results show that this approach yields predictions for the bistatic scattering cross section that are accurate over a broad range of surface parameters. (AN).

Electromagnetic wave scattering from randomly rough surfaces in the presence of scatterers is an active, interdisciplinary area of research with myriad practical applications in fields such as optics, acoustics, geoscience and remote sensing. In this book, the Method of Moments (MoM) is applied to compute the field scattered by scatterers such as canonical objects (cylinder or plate) or a randomly rough surface, and also by an object above or below a random rough surface. Since the problem is considered to be 2D, the integral equations (IEs) are scalar and only the TE (transverse electric) and TM (transverse magnetic) polarizations are addressed (no cross-polarizations occur). In Chapter 1, the MoM is applied to convert the IEs into a linear system, while Chapter 2 compares the MoM with the exact solution of the field scattered by a cylinder in free space, and with the Physical Optics (PO) approximation for the scattering from a plate in free space. Chapter 3 presents numerical results, obtained from the MoM, of the coherent and incoherent intensities scattered by a random rough surface and an object below a random rough surface. The final chapter presents the same results as in Chapter 3, but for an object above a random rough surface. In these last two chapters, the coupling between the two scatterers is also studied in detail by inverting the impedance matrix by blocks. Contents 1. Integral Equations for a Single Scatterer: Method of Moments and Rough Surfaces. 2. Validation of the Method of Moments for a Single Scatterer. 3. Scattering from Two Illuminated Scatterers. 4. Scattering from Two Scatterers Where Only One is Illuminated. Appendix. Matlab Codes. About the Authors Christophe Bourlier works at the IETR (Institut d’Electronique et de Télécommunications de Rennes) laboratory at Polytech Nantes (University of Nantes, France) as well as being a Researcher at the French National Center for Scientific Research (CNRS) on electromagnetic wave scattering from rough surfaces and objects for remote sensing applications and radar signatures. He is the author of more than 160 journal articles and conference papers. Nicolas Pinel is currently working as a Research Engineer at the IETR laboratory at Polytech Nantes and is about to join Alyotech Technologies in Rennes, France. His research interests are in the areas of radar and optical remote sensing, scattering and propagation. In particular, he works on asymptotic methods of electromagnetic wave scattering from random rough surfaces and layers. Gildas Kubické is in charge of the “Expertise in electroMagnetism and Computation” (EMC) laboratory at the DGA (Direction Générale de l’Armement), French Ministry of Defense, where he works in the field of radar signatures and electromagnetic stealth. His research interests include electromagnetic scattering and radar cross-section modeling.

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.