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The NATO Advanced Study Institute on Adaptive Methods in Underwater Acoustics was held on 30 July - 10 August 1984 in LLineburg, Germany. The Institute was primarily concerned with signal processing for underwater appl ica tions. The majority of the presentations, when taken together, yield a definite picture of the present status of understanding of adaptive and high resolution processing, setting out the progress achieved over the past four years together with the major problem areas remaining. Major effort was made to obtain a commensurate contribution of tutorial and advanced research papers. It is my hope that the material in this volume may be equally well suited for students getting an introduction to some of the basic problems in underwater signal processing and for the professionals who may obtain an up-to-date overview of the present state of the art. This might be especially useful in view of the controversy and lack of adequate interrelationships which have marked this rapidly expanding field in the past. Practical reinforcement of this picture is provided by the material concerning digital and optical processing technology, giving some guidance to achievable adaptive and high resolution techniques with current processing devices. The formal programme was extended and detailed by a series of six evening work shops on specific topics, during which informal discussions took place among the participants. Summaries of these workshops are also included in these Proceedings.
This book contains the papers that were accepted for presentation at the 1988 NATO Advanced Study Institute on Underwater Acoustic Data Processing, held at the Royal Military College of Canada from 18 to 29 July, 1988. Approximately 110 participants from various NATO countries were in attendance during this two week period. Their research interests range from underwater acoustics to signal processing and computer science; some are renowned scientists and some are recent Ph.D. graduates. The purpose of the ASI was to provide an authoritative summing up of the various research activities related to sonar technology. The exposition on each subject began with one or two tutorials prepared by invited lecturers, followed by research papers which provided indications of the state of development in that specific area. I have broadly classified the papers into three sections under the titles of I. Propagation and Noise, II. Signal Processing and III. Post Processing. The reader will find in Section I papers on low frequency acoustic sources and effects of the medium on underwater acoustic propagation. Problems such as coherence loss due to boundary interaction, wavefront distortion and multipath transmission were addressed. Besides the medium, corrupting noise sources also have a strong influence on the performance of a sonar system and several researchers described methods of modeling these sources.
This series of volumes constitutes an outstanding collection of contributions by the most active research workers in the area of acoustics and mechanics. It brings the reader up to date on the status of the various aspects of research in this field. The volumes should preserve their value for a long time, as they represent a monument to the achievements of human research capabilities in the underwater-acoustics aspects of the environment.
Describes the ideas and associated mathematical concepts behind signal to noise ratio and target detectability.
In its relentless pursuit of further knowledge, science tends to compartmentalize. Over the years the pursuit of What might be called geophysical acoustics of the sea-surface has languished. This has occured even through there are well-developed and active research programs in underwater acoustics, ocean hydrodynamics, cloud and precipitation physics, and ice mechanics - to name a few - as well as a history of engineering expertise built on these scientific fields. It remained to create a convergence, a dialogue across disciplines, of mutual benefit. The central theme of the Lerici workshop, perhaps overly simplified, was 'What are the mechanisms causing ambient noise at the upper surface of the ocean?' What could hydrodynamicists contribute to a better understanding of breaking wave dynamics, bubble production, ocean wave dynamics, or near-surface turbulence for the benefit of the underwater acoustics community? What further insights could fluid dynamicists gain by including acoustic measurements in their repertoire of instrumentation? While every attendee will have his or her percep tions of details, it was universally agreed that a valuable step had been taken to bring together two mature disciplines and that significant co-operative studies would undoubtedly follow. The scope of the workshop was enlarged beyond its original intent to also include the question of ice-noise generation. The success of this decision can be seen in high quality of the presentations. the contribution of its disciples in the other workshop discussions and the heightened awareness and interest of we other novices.

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United States. National Environmental Satellite, Data, and Information Service. Library and Information Services Division

Published: 1983

Total Pages: 606


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This paper describes the results of current research at DREA in which techniques of optimum array processing are being applied to active sonar. We are presenting these results at the Advanced Study Institute in order to illustrate some actual applications for such processing and to point out some of the practical considerations which arise in real systems. In particular, the paper concerns the problems which arise when the individual sensor elements have a complicated directivity pattern themselves. This is a common phenomenon in active systems where the receiving sensors are complex resonant structures and are housed in a dome or towed body presenting various baffling and diffraction effects. Most treatments of array processing consider ideal elements which have well behaved directivity properties and are transparent to the field. The results of this paper show that where these properties are not met, careful in situ array measurements are required, and even with such measurements practical array gains may not be as good as predictions based on ideal sensors.