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Oceanic Engineering, IEEE Journal of

Issue 3 • Date July 2008

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Displaying Results 1 - 15 of 15
  • Table of contents

    Publication Year: 2008 , Page(s): C1
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  • IEEE Journal of Oceanic Engineering publication information

    Publication Year: 2008 , Page(s): C2
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  • Estimation of Shear Wave Speed in Ocean-Bottom Sediment Using Electromagnetic Induction Source

    Publication Year: 2008 , Page(s): 233 - 239
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1807 KB) |  | HTML iconHTML  

    An experiment for studying the shear wave speed in ocean-bottom sediment using Scholte pulse waves was conducted on a shelf in the East China Sea. To generate Scholte pulse waves, we developed a new electromagnetic induction source, which was placed at 100-m depth on the seafloor and was remotely controlled on board through a 1000-m-long cable. A Scholte pulse propagating in sandy sediment was then measured using a couple of geophones placed on the seafloor at a distance of 100 m from the source. The dispersion property of the Scholte waves was obtained by applying a multiple filter technique (MFT) to the observed waves. We then obtained the shear wave speed structure, i.e., the depth dependency of the shear wave speed in the sediment, by applying an inversion method based on a genetic algorithm (GA). The estimated speed was about 100 m/s near the bottom and increased with depth. The power was a close match to the estimated depth-speed profile, as reported previously by Hamilton [E. L. Hamilton, Geophysics, vol. 41, pp. 985-996, 1976]. View full abstract»

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  • High-Resolution Geoacoustic Characterization of the Seafloor Using a Subbottom Profiler in the Gulf of Lion

    Publication Year: 2008 , Page(s): 240 - 254
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3375 KB) |  | HTML iconHTML  

    Subbottom profilers are commonly used to explore the first sediment layers below the seafloor. Recent narrowbeam profilers achieve improved performances in terms of signal-to-noise ratio (SNR) and resolution. Thus, the potential of these systems for near real-time geoacoustic characterization of sediments is high and is worth being specifically explored. This paper presents several methods to estimate geoacoustic parameters such as the absorption, the reflectivity, and the impedance contrast. These procedures are tested against real data collected with the SBP 120 subbottom profiler during the CALIbration MEthodology for Recognition of the Ocean bottom (CALIMERO) experiment. It is shown that the absorption and impedance contrast estimates are fully consistent with in situ measurements, which tends to confirm the possibility of near real-time characterization of sediment layers. View full abstract»

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  • Parameter Estimate Biases in Geoacoustic Inversion From Neglected Range Dependence

    Publication Year: 2008 , Page(s): 255 - 265
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (590 KB) |  | HTML iconHTML  

    This paper shows that neglecting environmental range dependence in matched-field inversion (MFI) results in biased theory errors that lead to biased geoacoustic parameter estimates using standard inversion methods. Two approaches are used to investigate this issue. The first considers the distribution of optimal parameter estimates obtained from a large number of range-independent inversions of synthetic data generated for random range-dependent environments. The second applies Bayesian inversion and computes marginal uncertainty distributions for geoacoustic parameters, neglecting environmental range dependence. Both hard- and soft-bottom environments are considered at a number of scales of lateral variability for water depth and seabed sound speed. While the use of multifrequency data reduces the variability of the parameter estimates, it does not generally reduce parameter biases and increases biases in some cases. The biases appear to result from additional losses in range-dependent propagation, which are compensated for in range-independent inversion by adjusting geoacoustic parameters to decrease the seabed reflection coefficient. The effects of range dependence differ for different environments, with the soft-bottom case sensitive to range-dependent sound speed and the hard-bottom case sensitive to range-dependent water depth. View full abstract»

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  • The Dependence of Fusion Gain on Signal-Amplitude Distributions and Position Errors

    Publication Year: 2008 , Page(s): 266 - 277
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (677 KB) |  | HTML iconHTML  

    This paper considers statistical detection theory for a system of two geographically distributed sensors. The performance of the two main fusion rules (OR and AND) is evaluated in the absence and presence of position errors in the observations, by means of receiver operating characteristics (ROC) curves. The analysis is restricted to three distributions that are representative of a Rician: Rayleigh, one-dominant-plus-Rayleigh (1D+R), and nonfluctuating signal amplitude. Rice's distribution is considered to be relevant for sonar and radar applications. In the absence of position errors, the performance is derived theoretically. It is shown that the best fusion rule depends on the assumed signal amplitude distribution and on the signal-to-noise ratio (SNR). Under operational conditions, position inaccuracies of the multiple observations are of main importance, raising association problems. In this case, the ROC curves are evaluated by means of simulations. It is found that position errors degrade detection performance by 3-6 dB if the AND fusion is used, whereas OR fusion is hardly affected. View full abstract»

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  • Localization in Airborne Multistatic Sonars

    Publication Year: 2008 , Page(s): 278 - 288
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1285 KB) |  | HTML iconHTML  

    Location of a target detected by an air-deployed multistatic sonar can be determined using various cross fixes based on signal/echo time-of-arrival data and bearings from the sonobuoys involved in the contact. The resultant multiple measurements of the target location generally differ from each other and are not precise due to the input errors such as the sonobuoy positioning, target bearing, and temporal errors. To combine these individual measurements into an estimate that has the minimal mean square error, we employ the Wiener filter. We examine how this estimation error depends on the input errors and assess the extent to which the reduction of sonobuoy positioning errors can improve contact localization. View full abstract»

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  • Optimal Range-Difference-Based Localization Considering Geometrical Constraints

    Publication Year: 2008 , Page(s): 289 - 301
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (755 KB) |  | HTML iconHTML  

    This paper proposes a new type of algorithm aimed at finding the traditional maximum-likelihood (TML) estimate of the position of a target given time-difference-of-arrival (TDOA) information, contaminated by noise. The novelty lies in the fact that a performance index, akin to but not identical with that in maximum likelihood (ML), is a minimized subject to a number of constraints, which flow from geometric constraints inherent in the underlying problem. The minimization is in a higher dimensional space than for TML, and has the advantage that the algorithm can be very straightforwardly and systematically initialized. Simulation evidence shows that failure to converge to a solution of the localization problem near the true value is less likely to occur with this new algorithm than with TML. This makes it attractive to use in adverse geometric situations. View full abstract»

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  • Bathymetric Sidescan Sonar Bottom Estimation Accuracy: Tilt Angles and Waveforms

    Publication Year: 2008 , Page(s): 302 - 320
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (662 KB) |  | HTML iconHTML  

    This paper presents a detailed analysis of bottom estimation performance of bathymetric sidescan sonar. Both general and closed-form expressions for the cross correlations of the received backscatter across a receive array are determined for a square pulse, match-filtered square pulse, and a chirp Gaussian pulse. The closed-form expressions clearly show the contributions that the various error mechanisms make to the correlation. Through geometry, simulation, and the Cramer-Rao lower bound (CRLB), it is demonstrated that when the array is tilted, a double-angle region results, which requires two angles to be estimated rather than just one, if the location of the bottom is to be determined correctly. Estimating two angles requires an array with at least three elements as opposed to two elements typically employed in simple relative-phase bathymetric sidescan sonar. It is shown through simulation that multiple angle estimates made with a simple linear prediction algorithm attain estimates near the CRLB and that the CRLB can be used to establish confidence limits. The bottom estimation performance related to a match-filtered Gaussian pulse and Gaussian chirp pulse are compared with that obtained with a match-filtered square pulse. Little difference in performance is found except when the angle estimation accuracy is thermal noise limited and then the chirp pulse performs better because of the higher resultant snr. A simple approximation procedure for predicting estimation performance is developed along with conditions for its application. Examples of bottom estimation performance are given for different array sizes, tilt angles, frequencies, and water types. View full abstract»

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  • Underwater Acoustic Communications: Long-Term Test of Turbo Equalization in Shallow Water

    Publication Year: 2008 , Page(s): 321 - 334
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2456 KB) |  | HTML iconHTML  

    Acoustic telemetry sea trials lasting for three months with experiment periods of 7 h have been carried out, using a turbo receiver. The communication channel is shallow; the depth is approximately 10 m, and the range is 850 m, showing variable multipath. The wind speed and the sound-speed profile (SSP) are measured during some of the experiments. The results show reliable communication over the entire period and performance improvement of the turbo receiver compared to a decision feedback equalizer (DFE) used as reference receiver. The noise in the experiment data suggests significant deviations from the Gaussian assumption, and analysis of turbo receiver performance under heavy-tailed noise is presented. View full abstract»

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  • Energy Consumption Model for a Broadband Shallow-Water Acoustic Communications Network

    Publication Year: 2008 , Page(s): 335 - 340
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (610 KB) |  | HTML iconHTML  

    A multistatic active sonar system with several widely distributed sensors must share information between the sensors. If acoustic communication is the means used to share information, it can consume a significant fraction of the system's total energy budget. In this communication, an energy consumption model is developed for a shallow-water acoustic communications network. The model includes the environmental factors like the sound-speed profile in the water column and the composition of the seabed. The model uses the waveguide invariant concept to incorporate efficiently the broadband nature of the communications signals. Numerical results demonstrate how relaying messages between intermediate sensors can save substantial energy compared to direct communications. The calculations also show that energy consumption can vary by more than an order of magnitude depending on the seabed composition. View full abstract»

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  • Spatial Focusing and Intersymbol Interference in Multiple-Input–Single-Output Time Reversal Communication Systems

    Publication Year: 2008 , Page(s): 341 - 355
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1623 KB) |  | HTML iconHTML  

    In this paper, we study a multiple-input-single-output (MISO) underwater communication system that applies time reversal (TR) to transmit signals so that they focus spatially and compress temporally on the intended receiver. Our simulations model an underwater acoustic channel as a waveguide, and we investigate the cases of a waveguide both with and without random inhomogeneities. We investigate physical TR metrics and communications related performance indicators. The results of our simulations show that spatial focusing depends strongly on the delay spread ( DS ) , as has been seen in experiments. This physical property of TR could be exploited in communication systems where signal coherence is desired only at the receiver location. However, in the simulations, we find that while spatial compression increases with DS in a robust way (i.e., even when inhomogeneities exist), time compression does not increase with DS. Moreover, physical measures of the temporal compression (temporal peak-to-sidelobe ratio) do not improve with waveguide inhomogeneities. Nevertheless, TR reduces intersymbol interference (ISI) at the receiver as DS increases for both types of waveguides, which is an important effect for efficient, high-speed communication. In addition to TR, preequalization at the transmitter can ideally eliminate ISI without significantly affecting spatial compression. However, this preequalization causes a reduction of received power, which may be acceptable when the signal-to-noise ratio (SNR) at the receiver is high. View full abstract»

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  • Special issue on Non-Rayleigh reverberation and clutter

    Publication Year: 2008 , Page(s): 356
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  • IEEE Oceanic Engineering Society Information

    Publication Year: 2008 , Page(s): C3
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  • Blank page [back cover]

    Publication Year: 2008 , 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