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This paper investigated methods for passive estimation of the bearing to a slowly moving acoustically radiating source. The mathematics for the solution to such a problem is analogous to estimating the time delay (or group delay) between two time series. Since the estimation of time delay is intimately related to the coherence between two time series, a summary of the properties of coherence is presented. (Author).
The summer school held in Portovenere followed a tutorial format with the purpose of familiarizing postdoctoral or postgraduate students in the basic theories and up-to-date applications of present knowledge. Although, from a teaching point of view, a certain areount of overlapping is always useful, in order to avoid excessive duplication direct contact between lecturers expert in the same subject was encouraged during the preparation phase. In recent years computer facilities and theoretical implementa tion have considerably increased the possibility of solving problems relating to signal detection in noise. Any type of communication may take advantage of signal processing principles, including any type of physical measurement that can be considered as a non-semantic and/or quasi-semantic communication. Since signal processing techniques are common to many branches of science (telecommunications, radar, sonar, seismology, geophysics, nuclear research, space research and others), the advanced and sophisticated levels reached singularly in anyone of them could be used to the advantage of the others. In particular, underwater acoustics is a discipline which, to some extent, represents a practical general model that has permitted the development of signal processing techniques suitable to meet data reduction and interpretation needs of other branches of science. This ASI consequently underlined the inter-disciplinarity of signal proces sing in order that the principles of outstanding methods developed in one field may be adapted to others.
Sections 1-2. Keyword Index.--Section 3. Personal author index.--Section 4. Corporate author index.-- Section 5. Contract/grant number index, NTIS order/report number index 1-E.--Section 6. NTIS order/report number index F-Z.
This study investigates methodologies for passive estimation of the bearing to a slowly moving acoustically radiating source. The mathematics for the solution to such a problem is analogous to estimating the time delay (or group delay) between two time series. The estimation of time delay is intimately related to the coherence between two time series. New results on using coherence to provide information about linear and nonlinear systems are presented. The maximum likelihood (ML) estimate of time delay is derived; the explicit dependence of the estimate on coherence is evident in the realization in which the two time series are prefiltered (to accentuate frequency bands of high coherence) and subsequently crosscorrelated. Also included are statistics of the estimates of the magnitude-squared coherence (MSC), including the probability density function, the cumulative distribution function, and the m-th moment of the MSC estimate. A complete discussion of the bias and the variance of the MSC estimates is presented. The receiver operating characteristics of a linearly thresholded coherence estimation detector are also presented. A general FORTRAN 4 computer program using the fast Fourier transform to estimate time delay is given.
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.
Passive acoustic monitoring is increasingly used by the scientific community to study, survey and census marine mammals, especially cetaceans, many of which are easier to hear than to see. PAM is also used to support efforts to mitigate potential negative effects of human activities such as ship traffic, military and civilian sonar and offshore exploration. Walter Zimmer provides an integrated approach to PAM, combining physical principles, discussion of technical tools and application-oriented concepts of operations. Additionally, relevant information and tools necessary to assess existing and future PAM systems are presented, with Matlab code used to generate figures and results so readers can reproduce data and modify code to analyse the impact of changes. This allows the principles to be studied whilst discovering potential difficulties and side effects. Aimed at graduate students and researchers, the book provides all information and tools necessary to gain a comprehensive understanding of this interdisciplinary subject.