Novel, accurate and computationally efficient methods for wave-based subsurface imaging in acoustic and elastic media are developed. The methods are based on Arbitrarily Wide-Angle Wave Equations (AWWE), which are highly-accurate space-domain one-way wave equations, formulated in terms of displacement components. Main contributions of this research are as follows. (I) Acoustic-AWWE Imaging, a new time-domain migration technique that is highly accurate for imaging steep dips in heterogeneous media. Similar in form to conventional 15 & deg; equation, the acoustic AWWE is implemented using an efficient double-marching explicit finite-difference scheme. Its accuracy and efficiency is studied both analytically and through numerical experiments. The method is able to achieve highly accurate images with only a few times the computational cost of the conventional low-order methods. (II) A new class of highly-accurate Absorbing Boundary Conditions (ABCs) for modeling and imaging with high-order one-way wave equations and parabolic equations. These ABCs, are developed using special imaginary-length finite elements. They effectively absorb the incident wave front and generate artifact-free images with as few as three absorbing layers. They are essential tools in imaging in truncated domains and underwater acoustics. (III) Elastic-AWWE imaging: The first high-order space-domain displacement-based elastic imaging method is developed in this research. The method, which is applicable to complex elastic media, is implemented using a unique downward continuation technique. At each depth step, a half-space is attached to the physical layer to simulate one-way propagation. The half-space is effectively approximated using special imaginary-length finite elements. The method is eventually implemented in frequency-space domain using a finite difference method. Numerical instabilities due to improper mapping of complex wave modes are suppressed by rotating the AWWE parameters in complex wav.

Wave-equation-based parameter estimation techniques can retrieve accurate and high-resolution subsurface physical properties from seismic data acquired close to the surface of the Earth. In fact, multiple acoustic full-waveform inversion methods have been proposed over the years to retrieve the P-wave velocity of the subsurface. Moreover, researchers have extended full-waveform inversion approaches to estimate anisotropic and absorption parameters as well. Nowadays, some applications of elastic full-waveform inversion can also be found. However, given its prohibitive computational cost compared to the acoustic counterpart, elastic wave-equation inversion workflows still have limited applicability within seismic exploration datasets. To tackle this challenge, I propose a novel wave-equation-based elastic parameter estimation workflow based on wave-equation operators. I refer to the entire approach as target-oriented elastic full-waveform inversion. The method is composed of two steps. In the first one, I apply an extended linearized waveform inversion to the surface data. The obtained subsurface image is then employed to synthesize data as if they were acquired close to a target area. Finally, this dataset is inverted using an elastic full-waveform inversion workflow to estimate the subsurface elastic parameters. I demonstrate its efficacy on a 2D synthetic test and an ocean-bottom-node dataset acquired in the Gulf of Mexico, showing its ability to retrieve the elastic parameters of potential subsurface prospects. Compared to the elastic inversion of the surface dataset, the proposed method has a computational cost lower by two orders of magnitude.

Novel physical solutions, including new results in the field of adaptive methods and inventive approaches to inverse problems, original concepts based on high harmonic imaging algorithms, intriguing vibro-acoustic imaging and vibro-modulation technique, etc. were successfully introduced and verified in numerous studies of industrial materials and biomaterials in the last few years. Together with the above mentioned traditional academic and practical avenues in ultrasonic imaging research, intriguing scientific discussions have recently surfaced and will hopefully continue to bear fruits in the future. The goal of this book is to provide an overview of the recent advances in high-resolution ultrasonic imaging techniques and their applications to biomaterials evaluation and industrial materials. The result is a unique collection of papers presenting novel results and techniques that were developed by leading research groups worldwide. This book offers a number of new results from well-known authors who are engaged in aspects of the development of novel physical principles, new methods, or implementation of modern technological solutions into current imaging devices and new applications of high-resolution imaging systems. The ultimate purpose of this book is to encourage more research and development in the field to realize the great potential of high resolution acoustic imaging and its various industrial and biomedical applications.

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

Describing and evaluating the basic principles and methods of subsurface sensing and imaging, Introduction to Subsurface Imaging is a clear and comprehensive treatment that links theory to a wide range of real-world applications in medicine, biology, security and geophysical/environmental exploration. It integrates the different sensing techniques (acoustic, electric, electromagnetic, optical, x-ray or particle beams) by unifying the underlying physical and mathematical similarities, and computational and algorithmic methods. Time-domain, spectral and multisensor methods are also covered, whilst all the necessary mathematical, statistical and linear systems tools are given in useful appendices to make the book self-contained. Featuring a logical blend of theory and applications, a wealth of color illustrations, homework problems and numerous case studies, this is suitable for use as both a course text and as a professional reference.

The Special Issue is focused on recent and upcoming advances in the combined application of remote sensing and applied geophysics. Applied geophysics analyzes the distribution of physical properties in the subsurface for a wide range of geological, engineering, and environmental applications at different scales. Seismic, electrical, magnetic, and electromagnetic methods are among the most applied and well-established geophysical techniques. These methods share the advantages of being non-invasive and exploring wide areas of investigation with respect to conventional methods (e.g., drilling). Geophysical surveys are usually carried out deploying or moving the appropriate instrumentation directly on the ground surface. However, recent technological advances have resulting in the development of innovative acquisition systems becoming more typical of the remote sensing community (e.g., airborne surveys). While applied geophysics mainly focuses on the subsurface, typical remote sensing techniques have the ability to accurately image the Earth’s surface with high-resolution investigations carried out by means of terrestrial, airborne, or satellite-based platforms. The integration of surface and subsurface information is often crucial for several purposes, including the processing of geophysical data, the characterization and time-lapse monitoring of surface and near-surface targets, and the reconstruction of highly detailed and comprehensive 3D models of the investigated areas. Recent contributions showing the added value of surface reconstruction and/or monitoring in the processing, interpretation, and cross-comparison of geophysical techniques for archaeological, environmental, and engineering studies are collected in this book. Pioneering geophysical acquisitions by means of innovative remote systems are also presented.