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Oceanic Engineering, IEEE Journal of

Issue 4 • Date Oct. 1993

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Displaying Results 1 - 20 of 20
  • Bit-serial CORDIC DFT computation with multidimensional systolic processor arrays

    Page(s): 508 - 519
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    It is shown how two square arrays, each comprising square root N* square root N CORDIC (Coordinate Rotation Digital Computer) processing elements (PEs), can be used to carry out an efficient two-dimensional (2-D) implementation of the N-point discrete Fourier transform (DFT), with O( square root N) time-complexity, producing N DFT coefficients every square root N time-steps, with fully systolic operation. Generalization to a multidimensional (m-D) solution is also discussed. The CORDIC PE is implemented in bit-serial form, being thus extremely efficient, in terms of speed/area product, and possessing simple interconnects. These characteristics facilitate the mapping of potentially thousands of such units, and hence of entire medium/large DFT modules, onto a single chip, when implemented with very-large-scale-integration (VLSI) or wafer-scale-integration (WSI) technologies.<> View full abstract»

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  • Acoustic model-based matched filter processing for fading time-dispersive ocean channels: theory and experiment

    Page(s): 447 - 465
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    It is shown that the performance of a conventional matched filter can be improved if the reference (replica) channel compensates for the distortion by the ocean medium. A model-based matched filter is generated by correlating the received signal with a reference channel that consists of the transmitted signal convolved with the impulse response of the medium. The channel impulse responses are predicted with a broadband propagation model using in situ sound speed measured data and archival bottom loss data. The relative performance of conventional and model-based matched filter processing is compared for large time-bandwidth-product linear-frequency-modulated signals propagating in a dispersive waveguide. From ducted propagation measurements conducted in an area west of Sardinia, the model-based matched filter localizes the depths of both the source and receiving array and the range between them. The peak signal-to-noise ratio for the model-based matched filter is always larger than that of the conventional filter View full abstract»

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  • Towed array shape estimation using Kalman filters-theoretical models

    Page(s): 543 - 556
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    The dynamical behavior of a thin flexible array towed through the water is described by the Paidoussis equation. By discretizing this equation in space and time a finite-dimensional state-space representation is obtained where the states are the transverse displacements of the array from linearity in either the horizontal or vertical plane. The form of the transition matrix in the state-space representation describes the propagation of transverse displacements down the array. The outputs of depth sensors and compasses located along the array are shown to be related in a simple, linear manner to the states. From this state-space representation a Kalman filter which recursively estimates the transverse displacements and hence the array shape is derived. It is shown how the properties of the Kalman filter reflect the physics of the propagation of motion down the array. Solutions of the Riccati equation are used to predict the mean square error of the Kalman filter estimates of the transverse displacements View full abstract»

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  • The estimation of the shape of an array using a hidden Markov model

    Page(s): 557 - 564
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    A hidden Markov model (HMM) technique for the estimation of the shape of a towed array is presented. It is assumed that there is a far-field source radiating sound containing possibly weak spectral lines. The technique uses either the Fourier coefficients at a given frequency computed from a single time block or the maximal eigenvector of a sample spectral covariance matrix. The technique is illustrated using several simulations. The results of these simulations indicate that the HMM technique yields shape and bearing estimates more accurate than those provided by a maximum-likelihood array shape estimation technique View full abstract»

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  • Real time time-frequency active sonar processing: a SIMD approach

    Page(s): 520 - 528
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    A paradigm for massively parallel processing of matched filters, replica correlators, ambiguity functions, and time-frequency distributions is presented, using a SIMD (single instruction stream, multiple data stream) programming methodology. It is shown that active sonar detection algorithms, as implemented by frequency domain processing, can be a natural match to a SIMD methodology, meeting the extensive computational needs of enhanced active sonar systems. The decomposition process is presented, and examples are given of the output of the computer program CMASP (Connection Machine Ambiguity Surface Processor). CMASP can provide real-time simultaneous multiple-beam, Doppler, and waveform replica correlations. Synthetic data are processed, and the corresponding CMASP outputs are displayed as three-dimensional ambiguity surfaces on networked graphic workstations. Because of efficient problem decomposition, other time-frequency processing can be exploited. Specifically, real-time instantaneous-like time-frequency distributions have been realized in which the data set is presented and processed as time-varying spectral representations View full abstract»

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  • Shallow water reverberation: normal-mode model predictions compared with bistatic towed-array measurements

    Page(s): 474 - 482
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    A normal-mode model for calculating reverberation in shallow water is presented. Some illustrative calculations are given for the bistatic case and for vertical and horizontal line-array receivers. Emphasis is on comparison with measurements of bistatic reverberation obtained at a shallow-water area in the Mediterranean. The data are from explosive sources received by a towed array, analyzed in one-tenth-decade frequency bands at subkilohertz frequencies. Model calculations for a flat-bottomed environment indicate a strong dependence on propagation conditions and a weak dependence on beam steering direction. Preliminary comparisons give quite good agreement between measured reverberation and model predictions, but point to the need for extending modeling efforts to handle range-dependent environments View full abstract»

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  • Robust high-resolution direction-of-arrival estimation via signal eigenvector domain

    Page(s): 491 - 499
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    A robust high-resolution direction-of-arrival (DOA) estimation approach for coherent/noncoherent sources is presented. The approach is based on the fact that the signal eigenvectors of the covariance matrix are a linear combination of the direction vectors that contain the DOA information. By applying a high-resolution frequency estimation algorithm to an element sequence from a combination of the signal eigenvectors, the approach achieves better performance at low SNR than the conventional methods. It is shown that the improvement in performance increases with the number of snapshots. For example, the resolution improvement of the proposed signal eigenvector domain approach over spatial-smoothed minimum-norm is about 2.5 dB and 7 dB for 20 and 100 snapshots, respectively View full abstract»

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  • A computerized system for assessing towed array sonar functionality and detecting faults

    Page(s): 529 - 542
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    A computer-based system that processes hydrophone and beam noise data from a towed horizontal line array sonar has been developed. The system also produces various displays that can be used to help assess the functionality of the sonar and to identify faults that cause degraded performance. The system-and various statistics used for characterizing or quantifying a given aspect of the sonar's performance are discussed. The results are presented in visual formats to aid in rapid assessment and quantification of the sonar's performance. Examples obtained from the system during recent towed array ambient noise measurement exercises are given to illustrate its utility for real-time performance monitoring and its capability for providing clues to aid in fault localization View full abstract»

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  • An overview of matched field methods in ocean acoustics

    Page(s): 401 - 424
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    A short historical overview of matched-field processing (MFP) is followed by background material in both ocean acoustics and array processing needed for MFP. Specific algorithms involving both quadratic and adaptive methods are then introduced. The results of mismatch studies and several algorithms designed to be relatively robust against mismatch are discussed. The use of simulated MFP for range, depth and bearing location is examined, using data from a towed array that has been tilted to produce an effective vertical aperture. Several experiments using MFP are reviewed. One successfully demonstrated MFP at megameter ranges; this has important consequences for experiments in global tomography. Some unique applications of MFP, including how it can exploit ocean inhomogeneities and make tomographic measurements of environmental parameters, are considered View full abstract»

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  • Ocean effects on time delay estimation requiring adaptation

    Page(s): 367 - 378
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    In active sonar and in passive sonar localization, time delay is a fundamental parameter whose extraction is vital to the sonar function. The underlying time delay parameter (or parameter vector) contains information about the acoustic source (or reflector) as seen through the ocean at a receiver. The ocean effects require sonar adaptation. A tutorial review of ocean effects in time delay estimation is provided, with references to benchmark work. It covers coherence, time-delay estimation, localization, time-varying time delay estimation, the complexity of the ocean environment, and depth estimation using mode matching View full abstract»

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  • The localization accuracy of a horizontal array observing a narrowband target with partial coherence

    Page(s): 466 - 473
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    The Cramer-Rao lower bound is used to assess the potential localization accuracy of a horizontal array observing a narrowband moving target. The narrowband signal received by the array is assumed to have only partial temporal coherence, which is modeled by taking the signal to be completely coherent over a data block but with an unknown absolute phase from block to block. A numerical example for a linear array illustrates the improvement in localization accuracy caused by an increase in the signal coherence time. The effect of target/array geometry is also studied View full abstract»

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  • Performance comparison of high resolution bearing estimation algorithms using simulated and sea test data

    Page(s): 438 - 446
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    The performance of both the Capon and the MUSIC high resolution bearing estimation algorithms is investigated using both simulated data and sea test data collected with an experimental planar array. The major problem with these estimators is their sensitivity to both system errors and deviations from the assumed noise model. To alleviate this problem, two methods for preprocessing the data before they are input into the high-resolution algorithm are investigated: beam space and sector focused stability. The performance of both high-resolution estimators is examined, using both types of preprocessing, and the results are compared with those for the standard element-space (ES) techniques, assuming both finite cross-spectral-matrix (CSM) averaging errors and weakening target strengths. For the Capon estimator the performance is only superior to the standard element space technique when the CSM is calculated using a small number of averages. For the MUSIC estimator, both preprocessing techniques give clearly superior results over standard space techniques, with the SFS preprocessor performing the best View full abstract»

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  • Range and depth estimation using a vertical array in a correlated multipath environment

    Page(s): 500 - 507
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    The effects of correlation between time-difference-of-arrival (TDOA) estimates on the localization of an underwater source in a direct-surface reflected propagation environment is investigated for a two-element vertical array with omnidirectional sensors. Expressions for the covariance matrix of the noisy TDOAs are derived. The results show that the estimated TDOAs are correlated and that the degree of correlation depends on the relative location of the source. Expressions for variances of range and depth estimators are developed using a least-squares technique. The results show that the expressions for variances of the range and depth estimators can be in error by as much as a factor 3.3 if the correlation among the TDOAs is ignored. The expressions for the covariances of the TDOAs and the expressions for the variances of the range and depth, which incorporate the correlation in the TDOAs, are corroborated with Monte Carlo simulations View full abstract»

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  • Fuzzy technology implemented in sonar systems

    Page(s): 483 - 490
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    Applications of fuzzy algorithms in the domain of sonar systems that have been implemented in the latest generation of Atlas sonar equipment are introduced. The aim is to provide an insight into the solution of problems from an application-oriented point of view. Classification of DEMON spectra and automatic target tracking by means of fuzzy systems are introduced and demonstrated with examples. A short introduction to fuzzy technology is given to support the understanding of the algorithms presented View full abstract»

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  • Remedying the effects of array shape distortion on the spatial filtering of acoustic data from a line array of hydrophones

    Page(s): 565 - 571
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    The effects of both small perturbations and large deformations to the array's shape on both conventional and adaptive beamformers are shown for two frequencies: the spatial Nyquist frequency (or design frequency) of the array and a frequency about three times greater. Large shape deformations lead to a decrease in the conventional beamformer's output power for a beam steered in the direction of the signal source, together with an increase in the sidelobe levels (or secondary maxima), while small perturbations in the array shape have little effect. Signal suppression is observed to be far greater for the adaptive beamformer because it is very sensitive to system errors. The imposition of a weight norm constraint on the adaptive beamformer reduces the signal suppression only for small shape perturbations array shape estimation techniques are needed to reduce signal suppression for large shape deformations. The adverse effects of a nonlinear array shape on both conventional and adaptive beamforming are shown to be substantially reduced by applying techniques that estimate the coordinates of the hydrophones prior to beamforming View full abstract»

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  • Towed array shape estimation using frequency-wavenumber data

    Page(s): 582 - 590
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    Towed array beamforming algorithms require accurate array shape information in order to perform properly. Very often, these algorithms assume the array is linear. Unfortunately, the mechanical forces on the array due to ship motion and sea dynamics can change the shape of the array, which degrades the performance of the beamforming algorithm. A data-driven approach to estimating the relative shape of a nominally linear array is presented. The algorithm is robust in that it optimally combines information contained in a wide band of frequencies and source bearings. At the heart of the algorithm is a maximum-likelihood (ML) estimation scheme. The Cramer-Rao lower bound is derived and compared to the performance of the ML estimator. The utility of the algorithm is verified using both simulated and actual towed array data experiments View full abstract»

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  • Acoustic models and sonar systems

    Page(s): 425 - 437
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    The basic types of acoustic models are reviewed. These include ray models, spectral integral models, normal mode models, parabolic equation modeling, and 3-D acoustic modeling. Their application to conventional sonar simulation problems is demonstrated. Examples of their use in more advanced signal processing applications are presented View full abstract»

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  • Fast maximum likelihood estimation of signal parameters using the shape of the compressed likelihood function

    Page(s): 388 - 400
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    A computationally efficient fast maximum-likelihood (FML) estimation scheme, which makes use of the shape of the surface of the compressed likelihood function (CLF), is proposed. The scheme uses only multiple one-dimensional searches oriented along appropriate ridges on the surface of the CLF. Simulations indicate that the performances of the proposed estimators match those of the corresponding maximum-likelihood estimators with very high probability. The approach is demonstrated by applying it to two different problems. The first problem involves the estimation of time of arrival and Doppler compression of a wideband hyperbolic frequency modulated (HFM) active sonar signal buried in reverberation. The second problem deals with estimating the frequencies of sinusoids. A threshold analysis of the proposed scheme is carried out to predict the signal-to-noise ratio (SNR) at which large estimation errors begin to occur, i.e., the threshold SNR, and its computational complexity is discussed View full abstract»

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  • Depth measurement of remote sources using multipath propagation

    Page(s): 379 - 386
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    A submerged acoustic source radiates narrowband Gaussian noise. Its signal propagates to a remote, large aperture vertical array over a multipath channel whose characteristics may or may not be fully known. The primary concern of this study is the accuracy of source depth estimates obtainable from the array output. Cramer-Rao bounds for the depth estimate are calculated. When the velocity profile is known exactly, the value of the bound is quite insensitive to the precise form of the velocity profile. A bound calculated from a constant velocity profile yields an excellent approximation for many situations likely to be encountered in practice. Introduction of an unknown parameter into the velocity profile has little effect on the Cramer-Rao bound for depth. However, a maximum likelihood estimator of depth working with an inaccurate value of the unknown parameter performs poorly. To obtain satisfactory performance, one must estimate the unknown parameters along with the source depth. Simulations demonstrate the success of this approach View full abstract»

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  • Towed array shape estimation using Kalman filters-experimental investigations

    Page(s): 572 - 581
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    The problem of estimating the shape of a towed array instrumented with either depth sensors, compasses, or both in a discrete-time state-space formulation is treated in a companion paper by D. A. Gray et al. (to appear), in which the state-space representation is derived from a dynamical model of the propagation of tow-point-induced motion down the array. A Kalman filter is derived to recursively estimate the shape of this towed array, and solutions to the Riccati equation are used to predict the mean square error of the Kalman filter array shape estimates. The present study investigates the performance of this Kalman filter approach as an array shape estimator using both simulated examples and sea trial data. Fundamental to the Kalman filter approach is the model that describes the dynamical behavior of the towed array. The results of an experimental program that was undertaken to validate this model are also presented View full abstract»

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Aims & Scope

The IEEE Journal of Oceanic Engineering (ISSN 0364-9059) is published quarterly by the IEEE Oceanic Engineering Society (IEEE OES). The scope of the Journal is the field of interest of the IEEE OES, which encompasses all aspects of science, engineering, and technology that address research, development, and operations pertaining to all bodies of water. This includes the creation of new capabilities and technologies from concept design through prototypes, testing, and operational systems to sense, explore, understand, develop, use, and responsibly manage natural resources.

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Meet Our Editors

Editor-in-Chief
N. Ross Chapman
School of Earth & Ocean Sciences
University of Victoria
3800 Finnerty Road
Victoria, BC V8P 5C2 Canada
chapman@uvic.ca