Download or read book Examination of Time Reversal Acoustics in Shallow Water and Applications to Underwater Communications written by António Adolfo Mendes Abrantes and published by . This book was released on 1999-06-01 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: Time-varying multipath propagation is considered the most important difficulty in shallow underwater acoustic (UWA) communications. To compensate for the time variability of the channel, the receiver must use an adaptive algorithm for adjusting its parameters. At high symbol rates, intersymbol interference caused by multipath propagation requires large adaptive filters, increasing the computational complexity at the receiver end. This thesis presents a time-reversal acoustic technique (implemented with a phase-conjugated array of PCA) that generates a spatio-temporal focus of acoustic energy at the receiver location which reduces distortions introduced by channel propagation (including multipath), allowing the use of low-complexity receivers. Numerical analysis shows that for different PCA geometries (element spacing and aperture sizes), the PCA focus footprint does not appear to significantly change its dimensions. Furthermore, the aperture size plays a more significant role than the number of array elements in a PC array design. Specific examples of novel UWA communication systems utilizing time-reversal focusing are introduced. Current simulation results suggest the potential for high data transfer rates compared to existing noncoherent UWA communication systems.

Download or read book Experimental Studies of Applications of Time Reversal Acoustics to Non Coherent Underwater Communications written by Michael G. Heinemann and published by . This book was released on 2000-03 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: The most difficult problem in shallow underwater acoustic communications is considered to be the time-varying multipath propagation because it impacts negatively on data rates. Computationally intensive and complex signal processing algorithms are required to compensate for symbol overlapping. This thesis presents results of a tank scale experiment to test Time-Reversal Acoustics (TRA) approach for high data rate binary transmissions. TRA can environmentally adapt the acoustic propagation effects of a complex medium. Our results show the suitability of the TRA approach in underwater acoustic communications. The results also show good focusing properties at an intended target location. The focal region extends over a few wavelengths, outside of which scrambling of the message occurs, offering natural encryption. Range shifts of the focal region could be achieved by frequency shifting. We found that the time focusing is aperture-size independent, but the spatial focusing is aperture-size dependent. Overall, we showed that our algorithm can accomplish a fast, secure, and stable communication scheme with low computational complexity.

Download or read book Underwater Acoustic Modeling and Simulation written by Paul C. Etter and published by CRC Press. This book was released on 2017-12-19 with total page 557 pages. Available in PDF, EPUB and Kindle. Book excerpt: Underwater Acoustic Modeling and Simulation, Fourth Edition continues to provide the most authoritative overview of currently available propagation, noise, reverberation, and sonar-performance models. This fourth edition of a bestseller discusses the fundamental processes involved in simulating the performance of underwater acoustic systems and emphasizes the importance of applying the proper modeling resources to simulate the behavior of sound in virtual ocean environments. New to the Fourth Edition Extensive new material that addresses recent advances in inverse techniques and marine-mammal protection Problem sets in each chapter Updated and expanded inventories of available models Designed for readers with an understanding of underwater acoustics but who are unfamiliar with the various aspects of modeling, the book includes sufficient mathematical derivations to demonstrate model formulations and provides guidelines for selecting and using the models. Examples of each type of model illustrate model formulations, model assumptions, and algorithm efficiency. Simulation case studies are also included to demonstrate practical applications. Providing a thorough source of information on modeling resources, this book examines the translation of our physical understanding of sound in the sea into mathematical models that simulate acoustic propagation, noise, and reverberation in the ocean. The text shows how these models are used to predict and diagnose the performance of complex sonar systems operating in the undersea environment.

Download or read book Underwater Acoustic Modeling and Simulation Fifth Edition written by Paul C. Etter and published by CRC Press. This book was released on 2018-03-15 with total page 776 pages. Available in PDF, EPUB and Kindle. Book excerpt: This newest edition adds new material to all chapters, especially in mathematical propagation models and special applications and inverse techniques. It has updated environmental-acoustic data in companion tables and core summary tables with the latest underwater acoustic propagation, noise, reverberation, and sonar performance models. Additionally, the text discusses new applications including underwater acoustic networks and channel models, marine-hydrokinetic energy devices, and simulation of anthropogenic sound sources. It further includes instructive case studies to demonstrate applications in sonar simulation.

Download or read book Oceans 2001 MTS IEEE written by and published by . This book was released on 2001 with total page 748 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Underwater Acoustic Communications Using Time Reversal written by Geoffrey Fred Edelmann and published by . This book was released on 2003 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Inverse Problems and Imaging written by Luis L. Bonilla and published by Springer. This book was released on 2009-06-19 with total page 207 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nowadays we are facing numerous and important imaging problems: nondestructive testing of materials, monitoring of industrial processes, enhancement of oil production by efficient reservoir characterization, emerging developments in noninvasive imaging techniques for medical purposes - computerized tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), X-ray and ultrasound tomography, etc. In the CIME Summer School on Imaging (Martina Franca, Italy 2002), leading experts in mathematical techniques and applications presented broad and useful introductions for non-experts and practitioners alike to many aspects of this exciting field. The volume contains part of the above lectures completed and updated by additional contributions on other related topics.

Download or read book The Journal of the Acoustical Society of America written by Acoustical Society of America and published by . This book was released on 2006 with total page 1222 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A History of the Acoustics Division of the Naval Research Laboratory written by Fred Tudor Erskine and published by . This book was released on 2013 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Acoustic Sensing Techniques for the Shallow Water Environment written by Andrea Caiti and published by Springer. This book was released on 2017-04-30 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thisvolume contains thecollection of papers from the second workshop on Expe- mental Acoustic Inversion Techniques for Exploration of theShallow Water Environment. Theworkshopthemefollowedtheoriginalconceptofthe rstworkshop, heldinCarvoeiro, Portugal, in 1999, i.e., to focus on experiments and experimental techniques for acoustic sensing in the shallow ocean. More than forty leading international scientists were invited to meet in the picturesque town of St. Angelo on the island of Ischia, in June 2004, to discuss progress in the application of new experimental techniques for exploration and assessment of shallowwater environments. Acoustic techniques provide the most effective means for remote sensing of ocean and sea oor processes, and for probing the structure beneath the sea oor. No other energy propagates as ef ciently in the ocean: radio waves and visible light are severely limited in range because the ocean is a highly conductive medium. However, sound from bre- ing waves and coastal shipping can be heard throughout the ocean, and marine mammals communicate acoustically over basin scale distances.

Download or read book Springer Handbook of Acoustics written by Thomas Rossing and published by Springer Science & Business Media. This book was released on 2007-06-21 with total page 1179 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is an unparalleled modern handbook reflecting the richly interdisciplinary nature of acoustics edited by an acknowledged master in the field. The handbook reviews the most important areas of the subject, with emphasis on current research. The authors of the various chapters are all experts in their fields. Each chapter is richly illustrated with figures and tables. The latest research and applications are incorporated throughout, including computer recognition and synthesis of speech, physiological acoustics, diagnostic imaging and therapeutic applications and acoustical oceanography. An accompanying CD-ROM contains audio and video files.

Download or read book Underwater Sound Propagation and Acoustic Communication in a Time varying Shallow Estuarine Environment written by Zheguang Zou and published by . This book was released on 2018 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: Estuaries are water regions that connect rivers and oceans, which are very important due to heavy traffic, fishery and other coastal engineering activities. Underwater acoustic technology offers a series of effective applications and technical supports for real-time monitoring and long-term preservation of the nature environment and ecosystem in these regions. However, estuaries are shallow waters with complicated temporal and spatial environmental variability, involving a variety of physical oceanographic processes, such as tidal water mixing and ocean winds/waves, which can significantly influence the underwater sound propagation and moreover, underwater acoustic communications. In order to perform reliably and effectively in such complex time-varying shallow-water ocean environments, next-generation underwater acoustic communication systems need an all new design based on the environmental variability of the physical ocean, which takes the environmental physics and time-varying variability into account and is able to adapt and switch to the optimal mode as the environment evolves. Therefore, a deep, comprehensive and thorough understanding of the link between the time-varying ocean environment, underwater acoustic channel, and underwater acoustic communication systems is highly required. ☐ This dissertation investigated the relationship between the shallow-water, time-varying environment of estuaries, the underwater sound propagation and underwater acoustic communications, which can help the design of underwater acoustic systems so that they can adapt the time-varying environment with wiser parameter configurations. In this dissertation, field data analysis, joint numerical modeling, together with a controllable laboratory experiment were used to study acoustic channel variability of a shallow estuary and its influence on the performance of underwater acoustic communications. This dissertation included four aspects: (a) Effect of water-column variation due to the tidal dynamics in an estuary on the underwater acoustic direct path; (b) Effect of time-varying surface roughness due to the wind-driven waves on underwater acoustic surface paths; (c) Numerically modeling the effect of time-varying wind-driven shallow-water waves on coherent underwater acoustic communications using a combined model; (d) Conducting a controllable laboratory experiment to investigate the time-varying wind-driven water waves on the performance of coherent and non-coherent underwater acoustic communications. ☐ The first two aspects focused on the link between the time-varying environment of an estuary and the underwater acoustic wave propagation. With field data analysis and joint numerical modeling, the time-varying variability of acoustic direct paths and surface-bounced paths from a high-frequency acoustic experiment conducted in the Delaware Bay estuary was explored. On one hand, periodical acoustic direct path fading was found in the tidal-straining Delaware Bay estuary, with the fading period as same as the semi-diurnal tide. Based on physical oceanography and ocean acoustics, the mechanism that causes the direct path fading and its link to the water dynamics of an estuary was investigated. On the other hand, the relationship between the acoustic surface paths and the surface wind speed was investigated, and the wind-influenced shallow-water time-varying channel was studied using field data analysis and a joint model combining physical oceanography and ocean acoustics. The joint numerical model, including a wind-wave model, a surface generation algorithm and a parabolic equation acoustic model, reproduced the relationship between the wind speed and surface reflection signals. ☐ The last two aspects applied the knowledge of underwater sound propagation in shallow estuaries into analyzing the performance of underwater acoustic communication systems, i.e., investigating how the fast fluctuation of a shallow-water environment (wind-driven waves) influences different fundamental modulation schemes for underwater acoustic communications. To better analyze the effect of environmental variability of the physical ocean on underwater acoustic communications, the surface condition was set as the only variation in the numerical modeling and the controllable laboratory experiment. On one hand, a combined model including physical oceanography, ocean acoustics, and underwater acoustic communication was used to study the time-varying underwater acoustic channel under different wind speeds, and the performance of the coherent acoustic communication (QPSK) system. On the other hand, a controllable laboratory experiment was conducted to investigate bit-error-rate (BER) performance of the MFSK (representing the non-coherent acoustic communication) and the QPSK (representing the coherent acoustic communication) acoustic modulations. ☐ The main conclusions of the dissertation are as follows. For the time-varying variability of underwater acoustic channel: (a) Due to the tidal-straining water dynamics of an estuary, periodical water column exchange between the seawater and the freshwater, up-refracting sound speed profile is more likely to form by the end of ebb tide, which redirects sound signal away from the deep receivers and creates shadow zone for the sound direct path; (b) In an open estuary, the acoustic pressure of surface-bounced paths decreases with increased wind speed, as a result of increased acoustic scattering due to the wind-driven surface roughness. For underwater acoustic communications: (c) Coherent acoustic communications are sensitive to the fast time-varying variability, and performance decrease significantly with increased wind speed, as a result of increased channel variability and decreased temporal coherence; (d) Non-coherent acoustic communications are less sensitive to the channel variability, and the reduced multipath signals due to wind-wave surface may improve the system performance. ☐ The key novelties of this dissertation include: (a) Using a joint model involving physical oceanography and ocean acoustics to study the effect of time-varying estuarine environment (water-column variations and wind-driven surface waves) on underwater sound propagation and the underwater acoustic channels. (b) Using an integrated model involving physical oceanography, ocean acoustics, and underwater acoustic communications to study the effect of time-varying estuarine environment (wind-driven surface waves) on underwater acoustic communications. (c) Using field experimental data, numerical modeling and controllable laboratory experiment to study the underwater sound propagation and underwater acoustic communications in a time-varying ocean environment.

Download or read book Ocean Time reversal Acoustics and Application to Reverberation Reduction written by Seongil Kim and published by . This book was released on 2002 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Japanese Journal of Applied Physics written by and published by . This book was released on 2005 with total page 1194 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Underwater Acoustic Modelling and Simulation Third Edition written by P.C. Etter and published by CRC Press. This book was released on 2003-12-08 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: Underwater Acoustic Modeling and Simulation examines the translation of our physical understanding of sound in the sea into mathematical models that can simulate acoustic propagation, noise and reverberation in the ocean. These models are used in a variety of research and operational applications to predict and diagnose the performance of complex sonar systems operating in the undersea environment. Previous editions of the book have provided invaluable guidance to sonar technologists, acoustical oceanographers and applied mathematicians in the selection and application of underwater acoustic models. Now that simulation is fast becoming an accurate, efficient and economical alternative to field-testing and at-sea training, this new edition will also provide useful guidance to systems engineers and operations analysts interested in simulating sonar performance. Guidelines for selecting and using available propagation, noise and reverberation models are highlighted. Specific examples of each type of model are discussed to illustrate model formulations, assumptions and algorithm efficiency. Instructive case studies demonstrate applications in sonar simulation.

Download or read book Digital Underwater Acoustic Communications written by Lufen Xu and published by Academic Press. This book was released on 2016-09-16 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: Digital Underwater Acoustic Communications focuses on describing the differences between underwater acoustic communication channels and radio channels, discusses loss of transmitted sound in underwater acoustic channels, describes digital underwater acoustic communication signal processing, and provides a comprehensive reference to digital underwater acoustic communication equipment. This book is designed to serve as a reference for postgraduate students and practicing engineers involved in the design and analysis of underwater acoustic communications systems as well as for engineers involved in underwater acoustic engineering. Introduces the basics of underwater acoustics, along with the advanced functionalities needed to achieve reliable communications in underwater environment Identifies challenges in underwater acoustic channels relative to radio channels, underwater acoustic propagation, and solutions Shows how multi-path structures can be thought of as time diversity signals Presents a new, robust signal processing system, and an advanced FH-SS system for multimedia underwater acoustic communications with moderate communication ranges (above 20km) and rates (above 600bps) Describes the APNFM system for underwater acoustic communication equipment (including both civil and military applications), to be employed in active sonar to improve its performance

Download or read book Acoustics Today written by and published by . This book was released on 2008 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt: