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Oceanic Engineering, IEEE Journal of

Issue 1 • Date Jan. 2009

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Displaying Results 1 - 14 of 14
  • Table of contents

    Page(s): C1
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  • IEEE Journal of Oceanic Engineering publication information

    Page(s): C2
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  • LOAPEX: The Long-Range Ocean Acoustic Propagation EXperiment

    Page(s): 1 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1669 KB) |  | HTML iconHTML  

    This paper provides an overview of the experimental goals and methods of the Long-range Ocean Acoustic Propagation EXperiment (LOAPEX), which took place in the northeast Pacific Ocean between September 10, 2004 and October 10, 2004. This experiment was designed to address a number of unresolved issues in long-range, deep-water acoustic propagation including the effect of ocean fluctuations such as internal waves on acoustic signal coherence, and the scattering of low-frequency sound, in particular, scattering into the deep acoustic shadow zone. Broadband acoustic transmissions centered near 75 Hz were made from various depths to a pair of vertical hydrophone arrays covering 3500 m of the water column, and to several bottom-mounted horizontal line arrays distributed throughout the northeast Pacific Ocean Basin. Path lengths varied from 50 km to several megameters. Beamformed receptions on the horizontal arrays contained 10-20-ms tidal signals, in agreement with a tidal model. Fifteen consecutive receptions on one of the vertical line arrays with a source range of 3200 km showed the potential for incoherent averaging. Finally, shadow zone receptions were observed on an ocean bottom seismometer at a depth of 5000 m from a source at 3200-250-km range. View full abstract»

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  • The Influence of Emitter and Receiver Motion on Acoustic Coherence in Shallow Water

    Page(s): 12 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (430 KB) |  | HTML iconHTML  

    This paper is aimed at studying the source and receiver motion effects on the energy and correlation characteristics of the acoustic field in shallow water. The statistical analysis is based on the radiation transport equation for the mutual coherence function (MCF) of the multimodal Doppler-shifted field. A general computer program has been elaborated to implement this theory for rough surface scattering by fully developed wind seas. Calculations of the expected total average acoustic intensity and two-point coherence function are presented. View full abstract»

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  • Matching a Permanent Magnet Synchronous Generator to a Fixed Pitch Vertical Axis Turbine for Marine Current Energy Conversion

    Page(s): 24 - 31
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1716 KB) |  | HTML iconHTML  

    Extracting energy from a free-flow marine current using a vertical axis fixed pitch turbine requires a generator that can handle varying speeds and loads, since such a turbine gives maximum power capture for a fixed tip speed ratio. A prototype of such a generator has been designed and constructed. In this paper, its variable speed and load operation is evaluated, both in terms of how the constructed generator performs in relation to simulations, and in terms of how the generator could perform with three different fixed pitch turbines. Measurements of root mean square (RMS) voltage and current differ 10% from simulations. Performance analysis with example turbines shows that the generator can match fixed tip speed ratio operation of several turbines for current speeds between 0.5 and 2.5 m/s. View full abstract»

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  • Buried Underwater Object Classification Using a Collaborative Multiaspect Classifier

    Page(s): 32 - 44
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3358 KB) |  | HTML iconHTML  

    In this paper, a new collaborative multiaspect classification system (CMAC) is introduced, which utilizes a group of collaborative decision-making agents capable of producing a high-confidence final decision based on features obtained over multiple aspects. It is also shown how CMAC can be modified to perform multiaspect classification using a decision feedback (DF) strategy. The system is then applied to a buried underwater target classification problem. The results show that CMAC provides excellent multiple-ping classification of mine-like objects while reducing the number of false alarms compared to other multiple-ping classification fusion systems such as nonlinear decision-level fusion (DLF). View full abstract»

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  • Estimation of K -Distribution Shape Parameter From Sonar Data: Sample Size Limitations

    Page(s): 45 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (225 KB) |  | HTML iconHTML  

    The K-distribution has been found to provide a good description of the probability density function (pdf) of the matched filter envelope of sonar signals backscattered from the seafloor. Furthermore, the scale and shape parameters that specify the K-distribution, under certain assumptions, have been related to physical descriptors of the seafloor. Specifically, the shape parameter has been related to the number of contributing scatterers and the scale parameter has been related to the average scatterer size. There exists, therefore, the possibility of estimating seafloor scattering properties by determining the shape and scale parameters of the K-distribution that best fits the signal returned from the seafloor. This paper investigates the relationship between data sample size and the accuracy to which K-distribution shape parameter can be determined. Computer-generated random data are considered and two types of test are used to study the ease with which the data distribution can be described. The Kolmogorov-Smirnov (KS) test and a parameter estimation technique based on the method of moments are used and it is shown that, for these tests, the sample size necessary to distinguish reliably between Rayleigh- and K-distributed data is proportional to the square of the shape parameter of the K-distribution. It is also shown that the sample size necessary to determine the shape parameter to the nearest integer value is proportional to the shape parameter raised to the fourth power. This proportionality is shown to be consistent with consideration of Cramer-Rao lower bound (CRLB). The implications for practical sonar scenarios are discussed. View full abstract»

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  • Combined Geoacoustic Inversion of Propagation and Reverberation Data

    Page(s): 51 - 62
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2104 KB) |  | HTML iconHTML  

    Sonar performance predictions in shallow water are strongly dependent on good knowledge of the geoacoustic and scattering properties of the seabed. One technique to extract information about the bottom is to use a towed source and a towed horizontal array. This towed system has been shown to be applicable for characterizing the bottom properties locally by inversion of the acoustic signals received directly on the towed array at short ranges. The same towed system has also been applied to extract bottom properties from long-range reverberation data providing effective bottom properties over a large area. However, independent geoacoustic inversion of the short-range propagation and long-range reverberation data can introduce low sensitivity and uncertainty in the extracted bottom properties. An attempt to resolve this low sensitivity and ambiguity is made by a simultaneous geoacoustic inversion of short-range propagation and long-range reverberation data with the intention of constraining the possible solutions of the bottom properties. View full abstract»

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  • Efficient Wideband Parameter Estimation Using Arbitrary Enveloped LFM Signals via Hermite Decompositions

    Page(s): 63 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (637 KB) |  | HTML iconHTML  

    Signals with finite time support are frequently used in active sonar and radar processing. In these applications, for efficient computations, it is necessary to have a compact description of the signals' shape and time evolution. For this purpose, the Hermite series expansions are used in this paper to approximate an arbitrary enveloped linear frequency modulated signal. The Hermite basis functions are based on the product of Hermite polynomials and a Gaussian function. The analytical expressions for the Fourier transform of linear frequency modulated (LFM) Hermite functions are presented. It is proposed to use the Fourier transform of LFM Hermite functions for efficient computation of the wideband cross-ambiguity function (WCAF) for target parameter estimation in active sonar processing. Efficient 2-D search methods are also proposed to obtain parameters from the WCAF. View full abstract»

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  • Acoustic Detection and Localization of a Turboprop Aircraft by an Array of Hydrophones Towed Below the Sea Surface

    Page(s): 75 - 82
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1632 KB) |  | HTML iconHTML  

    The acoustic spectrum of a propeller-driven aircraft is dominated by a series of spectral lines that are harmonically related to the blade rate (which is equal to the product of the propeller rotation rate and the number of blades on the propeller). We show that an array of acoustic sensors towed below the sea surface can be used for the passive detection and localization of such an aircraft. The acoustic energy from an aircraft is found to reach the subsurface sensors via two propagation paths: a bottom reflection path that enables the aircraft to be detected at long ranges, and a direct path that is present only when the aircraft passes overhead. For each of these paths, the observed variation with horizontal range of the Doppler shift in the blade rate closely matches the variation predicted by the simple model presented in this paper. Good agreement between theory and experiment is also obtained for the variation with horizontal range of the aircraft's apparent bearing. Thus, by using the observed Doppler shift and apparent bearing information, we were able to estimate the aircraft's horizontal range, speed, direction, and altitude. View full abstract»

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  • Attenuation Measurements Across Surface-Ship Wakes and Computed Bubble Distributions and Void Fractions

    Page(s): 83 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1328 KB) |  | HTML iconHTML  

    A surface ship's wake is composed of several hydrodynamic phenomena. A large part of that wake contains a mixture of air bubbles of various sizes in turbulent water. Eventually, as the wake ages, the turbulence subsides and bubbles begin to rise at rates that are determined by their sizes. These bubbles of various sizes and concentrations control the propagation of acoustic signals inside and across a wake. To further our understanding of these phenomena, a series of three continuous-wave (CW)-pulsed signals were transmitted across a wake as the wake aged. Each transmission contained a set of four 0.5-ms-long pulses. The 12 pulses ranged over frequencies from 30 to 140 kHz in 10-kHz steps. The acoustic attenuations across wakes that were due to varying bubble-size densities within the wakes were determined experimentally. From those data, estimates of the bubble densities as functions of the speed of the wake-generating ship, the wake's age, and acoustic frequency were calculated. From the bubble-density results, power-law fits and void fractions are calculated. The attenuation measurements were taken at 7.5-m intervals behind the wake-generating ship and continued for about 2 km. The experiment was run for wakes generated at ship speeds of 12- and 15-kn wakes, and the 15-kn run was repeated for consistence determination. The bubble densities were observed to have power-law forms with varying parameters with the strongest, for early ages, having an exponent of -3.6 and a void fraction of 4 x 10-7 , and with both diminishing for older wakes, as might be expected. View full abstract»

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  • Fluid-Filled Passive Sonar Calibration Spheres: Design, Modeling, and Measurement

    Page(s): 93 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (562 KB) |  | HTML iconHTML  

    Hollow spheres have long been used as simple underwater targets for testing acoustic projector systems. While spheres offer a mathematically simple shape with a resolvable scattering strength, their usage as a passive target has been less successful due to the complicated manner in which a hollow sphere scatters energy from its exterior and interior as a function of frequency and temperature. Furthermore, a sphere's aspect independent scattering requires a surface area that is physically much greater than a wavelength which in turn requires mechanical support systems that are also large, often with target strengths that rival that of the test target itself. This paper discusses the development of several thin-walled spheres, ranging in diameters from 0.1524 to 0.4953 m, filled with a high-density fluid, to be used collectively as calibrated underwater sonar targets in the 5-50-kHz frequency range and an additional 0.4953-m diameter sphere tested over the range of 5-120 kHz. The combination of the spherical shape and focusing effects of the fluid enhances the acoustic scattering strength of the sphere and produces a significantly greater backscattered response than a rigid sphere. A simple theoretical model is presented to compare several fill fluid possibilities and is then used to compare the chosen fluid, fluorolube, against measured data for each sphere. View full abstract»

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  • IEEE Oceanic Engineering Society Information

    Page(s): C3
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  • Blank page [back cover]

    Page(s): C4
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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.

Full Aims & Scope

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