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Oceanic Engineering, IEEE Journal of

Issue 1 • Date Jan. 2004

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Displaying Results 1 - 23 of 23
  • Table of contents

    Page(s): c1 - c4
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  • IEEE Journal of Oceanic Engineering publication information

    Page(s): c2
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  • Benchmarking geoacoustic inversion methods using range-dependent field data

    Page(s): 3 - 12
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB) |  | HTML iconHTML  

    Over the past decade, inversion methods have been developed and applied to acoustic field data to provide information about unknown ocean-bottom environments. An effective inversion must provide both an estimate of the bottom parameters and a measure of the uncertainty of the estimated values. This paper summarizes results from the Office of Naval Research (ONR)/Space and Naval Warfare Systems Command (SPAWAR) Geoacoustic Inversion Techniques Workshop, test cases 4 and 5. The workshop was held to benchmark present-day inversion methods for estimating geoacoustic profiles in shallow water. The format of the workshop was a blind test to estimate unknown geoacoustic profiles by inversion of measured acoustic transmission loss data in octave bands and reverberation envelopes. The data sets for test cases 4 and 5 were taken at two locations in shallow water, one in the East China Sea and the other along the southwest coast of Florida. The limitations of the data and the limits to the knowledge of the sites are discussed. In both cases, impulsive sources were used in conjunction with air-deployed sonobuoys. Since the measured data was incoherent, only methods consistent with total energy matching were applicable. Comparisons between the different inversion techniques presented at the workshop are discussed. For test cases 4 and 5, a precise metric was unavailable for comparison. View full abstract»

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  • Using the adaptive simulated annealing algorithm to estimate ocean-bottom geoacoustic properties from measured and synthetic transmission loss data

    Page(s): 13 - 28
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (976 KB) |  | HTML iconHTML  

    This paper presents the results obtained using the adaptive simulated annealing (ASA) algorithm to invert the test cases from the Geoacoustic Inversion Techniques Workshop held in May 2001. The ASA algorithm was chosen for use in our inversion software for its speed and robustness when searching the geoacoustic parameter solution space to minimize the difference between the observed and the modeled transmission loss (TL). Earlier work has shown that the ASA algorithm is approximately 15 times faster than a modified Boltzmann annealing algorithm, used in prior versions of our TL inversion software, with comparable fits to the measured data. Results are shown for the synthetic test cases, 0 through 3, and for the measured data cases, 4 and 5. The inversion results from the synthetic test cases showed that subtle differences between range-dependent acoustic model version 1.5, used to generate the test cases, and parabolic equation (PE) 5.0, used as the propagation loss model for the inversion, were significant enough to result in the inversion algorithm finding a geoacoustic environment that produced a better match to the synthetic data than the true environment. The measured data cases resulted in better fits using ASTRAL automated signal excess prediction system TL 5.0 than using the more sophisticated PE 5.0 as a result of the inherent range averaging present in the ASTRAL 5.0 predictions. View full abstract»

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  • Description of the Hamilton-Bachman smart rule (HBSR) inversion technique (IT) applied to impulsive source data from the 2001 IT workshop

    Page(s): 29 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2376 KB) |  | HTML iconHTML  

    An inversion technique (IT) is developed and preliminarily tested using data from the 2001 IT Workshop. This technique was developed using TL versus range data collected by the harsh environments program (HEP) and provided through the workshop. However, the IT developed here applies to all sonar systems, active and passive. The sonar-independent portion of the IT consists of a simulated annealing algorithm to be developed by Neumann et al. constrained by an expert system called the Hamilton-Bachman Smart Rules (HBSR), which was developed by the authors. This expert system constrains the geoacoustic model being inverted to realistic Hamilton-Bachman-type values, curve shapes, etc. The sonar-specific module of the IT is chosen based on the sonar frequency and models available to run at those frequencies. Two measured data cases from the workshop are presented and, due to the HBSR, good solutions were acquired in less than 50 iterations. View full abstract»

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  • Rapid geoacoustic characterization: applied to range-dependent environments

    Page(s): 43 - 50
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    The problem of rapid environmental assessment in a range-dependent environment is addressed. For rapid assessment, the exact geoacoustic parameters are not required, nor is it a requirement that the exact structure of the acoustic field (location of peaks and s) be matched by an acoustic prediction model. The parameters that are relevant are the overall transmission loss (incoherent TL), the time spread (τ), and the slopes of the range/frequency interference patterns (β, the waveguide invariant). The rapid geoacoustic characterization algorithm uses a homogeneous single-sediment layer overlying a hard acoustic basement model to optimally match the predicted acoustic observables with those estimated from data. The approach is presented here and is applied to the range-dependent benchmark cases TC1 and TC2 from the Inversion Techniques Workshop held in Gulfport, MS, in May 2001. The technique successfully reproduces the acoustic observables and estimates the sediment sound-speed, density, and attenuation profiles, as well as the sediment thickness. View full abstract»

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  • Preliminary analysis of the applicability of adiabatic modes to inverting synthetic acoustic data in shallow water over a sloping sea floor

    Page(s): 51 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    The May 2001 Geoacoustic Inversion Techniques Workshop provided synthetic transmission loss (TL) data for four cases with range-dependent shallow-water all-liquid environments. In two of these cases ("0" and "1"), the sea floor has constant slope and the geoacoustic model (GAM) is range independent. Cost functions have been computed using a new adiabatic-mode TL algorithm (which uses an exact velocity boundary condition at the sloping sea floor), as one parameter in the GAM is varied. Two frequencies (80 and 220 Hz) were selected. In case 0, the sea-floor slope is 0.0183 and the GAM comprises an inhomogeneous layer over a basement. The sea-floor sound-speed was selected as the variable parameter. The resulting cost minima at 80 and 220 Hz are displaced from the actual sound speed by 2.3 and 3.4 m/s, respectively. In case 1, the sea-floor slope is 0.012 and the GAM comprises one homogenous layer, five inhomogeneous layers, and a basement. The selected parameter was the sound-speed in the homogeneous layer. The corresponding cost minima are displaced by -1.2 and +1.1 m/s. The relative values of these four errors indicate that mode coupling increases with sea-floor slope and that there may be a dependence on frequency at the greater slope. View full abstract»

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  • Matched field processing (MFP)-based inversion method (SUB-RIGS) for range-dependent scenarios

    Page(s): 59 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1816 KB) |  | HTML iconHTML  

    This paper presents a variety of results. First, it examines propagation for the multiple-layer range-independent test case (Na) of Workshop97. Results indicate that, for 200 Hz, only one sediment layer plus a half-space are needed to describe that highly depth-variable bottom (originally consisting of 34 sediment layers over a half-space). Additionally, at 100 Hz, only two sediment layers plus a half-space give excellent accuracy while, at 25 Hz, at most three sediment layers plus a half-space are needed for high accuracy. These results point the way to the inversion method (SUB-RIGS) developed here and are applied to the workshop data. Second, this paper briefly examines model accuracy for our range-dependent field predictions. When an older and problematic propagation model code was used in the context of the Stennis Geoacoustic Inversion Techniques (GAIT) Workshop '01 calibration case (CAL), we found that the propagation predictions were off. These errors cause major problems for the TC1 inversion. Thus, SUB-RIGS was updated to use a more accurate-and far more efficient-propagation model (RAMGEO). A key point illustrated here is that it is not always clear when an embedded propagation code may need updating. Additionally, the CAL data are examined in terms of the sensitivity of various frequencies to various bottom parameters. These sensitivities also point the way toward the development of the SUB-RIGS method in which frequency/range behaviors are decoupled for various bottom parameters. Finally, this paper presents inversion estimates for the bottom parameters of the test case TC1 and of the calibration case CAL (both sloping bottoms) from the GAIT Workshop '01. The SUB-RIGS inversion method (not automated) is described and applied where frequency subspacing (as a function of range) plus reduced iterated grid searches determine layer properties. The method usually (but not necessarily) assumes: a linear bottom slope; up to three sediment layers over a half-space; segmented sound-speed profiles (assumed to be linear within a layer); densities (assumed to be constant within a layer); and sediment attenuation (assumed to be constant throughout except at the very low depths to eliminate false returns). This method does find- rather accurate sound-speed profiles for the layers. The sediment densities and attenuation (which have less effect on the propagation) are less accurately estimated. View full abstract»

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  • An investigation of algorithm-induced variability in geoacoustic inversion

    Page(s): 78 - 87
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    This paper investigates the inherent variability in the results of matched-field geoacoustic inversion algorithms. This algorithm-induced variability must be considered when interpreting inversion results in terms of environmental changes as a function of time or space. Fast simulated annealing (FSA), genetic algorithms (GA), and a hybrid algorithm (adaptive simplex simulated annealing; ASSA) are compared by performing multiple inversions of benchmark synthetic data (noise free and noisy) and acoustic data measured over both low- and high-speed sea-bed sediments in the MAPEX 2000 experiment. ASSA produced the lowest variability in inversion results for all cases, followed by GA and FSA. For the high-speed MAPEX 2000 case, the variability is essentially negligible, while for the low-speed case the variability is significant as compared with environmental variations reported in the literature. View full abstract»

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  • Rapid geoacoustic characterization using a surface ship of opportunity

    Page(s): 88 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB) |  | HTML iconHTML  

    The problem of rapid classification of the sea-floor sediment is addressed using horizontal line array (HLA) acoustic data from a passing surface ship. The data are beamformed to improve signal-to-noise ratio. The rapid geoacoustic characterization (RGC) algorithm involves extracting acoustic observables from the data (normalized striation slope, time spread, and transmission-loss slope). A simple single homogenous sediment layer over an acoustic half-space model is used to compute forward estimates of the acoustic observables. An exhaustive search over the two-parameter model is performed. The two parameters searched over are the sediment compressional speed (Cp), which is a polynomial function of the mean grain size (φ), and sediment thickness (H). This approach provides a real-time technique for classifying the sediment in a way that successfully reproduces the basic physics of propagation. View full abstract»

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  • Active rapid geoacoustic characterization using a seismic survey source

    Page(s): 100 - 109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1168 KB) |  | HTML iconHTML  

    A survey of received acoustic energy levels from a seismic profiler were performed in Long Beach Harbor, CA, for compliance with the Marine Mammal Protection Act (MMPA). In addition to direct acoustic measurements, a rapid geoacoustic inversion algorithm was applied to the data to estimate the sediment properties acoustically. This inversion algorithm has matching criteria based on time spread, range-frequency interference patterns, and the range dependence of transmission loss. Self-consistency was checked by comparing acoustic measurements with predictions based on the inversion. With an estimated geoacoustic profile, predictions of received levels as a function of position in the range-dependent environment of Long Beach Harbor were then performed. View full abstract»

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  • Acoustic radiation from a pulsating spherical cap set on a spherical baffle near a hard/soft flat surface

    Page(s): 110 - 117
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    Radiation of sound from a spherical piston, set in the side of a rigid sphere, undergoing harmonic radial surface vibrations in an acoustic halfspace is analyzed in an exact fashion using the classical method of separation of variables. The method of images in combination with the translational addition theorems for spherical wave functions is employed to take the presence of the flat boundary into account. The analytical results are illustrated with numerical examples in which the piston is pulsating near the rigid/compliant boundary of a water-filled halfspace. Subsequently, the basic acoustic field quantities such as the acoustic radiation impedance load and the radiation intensity distribution are evaluated for representative values of the parameters characterizing the system. Numerical results reveal the important effects of excitation frequency, source position, and cap angle on the acoustic radiation impedance load and the radiation intensity distribution. The presented work can lead to a better understanding of dynamic response of near-surface underwater transducers. View full abstract»

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  • Acoustic mode coupling by nonlinear internal wave packets in a shelfbreak front area

    Page(s): 118 - 125
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    A computational case study of coupled-mode 400-Hz acoustic propagation over the distance 27 km on the continental shelf is presented. The mode coupling reported here is caused by lateral gradients of sound-speed within packets of nonlinear internal waves, often referred to as solitary wave packets. In a waveguide having unequal attenuation of modes, directional exchange of energy between low- and high-loss modes, via mode coupling, can become time dependent by the movement of waves and can cause temporally variable loss of acoustic energy into the bottom. Here, that bottom interaction effect is shown to be sensitive to stratification conditions, which determine waveguide properties and, in turn, determine modal attenuation coefficients. In particular, time-dependent energy loss due to the presence of moving internal wave packets is compared for waveguides with and without a frontal feature similar to that found at the shelfbreak south of New England. The mean and variability of acoustic energy level 27 km distant from a source are shown to be altered in a first order way by the presence of the frontal feature. The effects of the front are also shown to be functions of source depth. View full abstract»

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  • Reverberation envelope statistics and their dependence on sonar bandwidth and scattering patch size

    Page(s): 126 - 137
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB) |  | HTML iconHTML  

    Increasing transmit waveform bandwidth in an active sonar-system results in an increase in the signal-to-reverberation power ratio in reverberation-limited environments, but also changes the probability density function of the reverberation envelope. A recent model that relates a description of the sonar system and environment to the parameters of the K-distribution predicts that the shape parameter (α) is proportional to range, beamwidth, and the density of scattering patches on the sea floor and is inversely proportional to bandwidth. In this paper, the bandwidth relationship is examined with real data from a low-frequency active sonar system with a towed array receiver. The inverse proportionality is observed at low bandwidths as a trend away from a Rayleigh-distributed envelope (decreasing α) as bandwidth increases. However, a trend back toward Rayleigh reverberation (increasing α) is observed as bandwidth continues to increase. Hypothesizing that the increase in α arises from over-resolving scattering patches in range and not in angle, the model of is extended to account for patch size relative to that of the sonar-resolution cell. The shape parameter of a moment-matched K-distribution derived from the extended model is then seen to provide a good fit to that estimated from the data. View full abstract»

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  • Pulse-length-tolerant features and detectors for sector-scan sonar imagery

    Page(s): 138 - 156
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1144 KB) |  | HTML iconHTML  

    This paper presents a neural-network-based system to detect small man-made objects in sequences of sector-scan sonar images created using signals of various pulse lengths. The detection of such objects is considered out to ranges of 150 m by using an experimental sector-scan sonar system mounted on a vessel. The sonar system considered in this investigation has three modes of operation to create images over ranges of 200, 400, and 800 m from the vessel using acoustic pulses of a different duration for each mode. After an initial cleaning operation performed by compensating for the motion of the vessel, the imagery is segmented to extract objects for analysis. A set of 31 features extracted from each object is examined. These features consist of basic object size and contrast features, shape moment-based features, moment invariants, and features extracted from the second-order histogram of each object. Optimal sets of 15 features are then selected for each mode and over all modes using sequential forward selection (SFS) and sequential backward selection (SBS). These features are then used to train neural networks to detect man-made objects in each sonar mode. By the addition of a feature describing the sonar's mode of operation, a neural network is trained to detect man-made objects in any of the three sonar modes. The multimode detector is shown to perform very well when compared with detectors trained specifically for each sonar mode setting. The proposed detector is also shown to perform well when compared to a number of statistical detectors based on the same set of features. The proposed detector achieves a 92.4% probability of detection at a mean false-alarm rate of 10 per image, averaged over all sonar mode settings. View full abstract»

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  • Multichannel moment detectors for transients in shallow-water noise

    Page(s): 157 - 168
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    This paper presents an evaluation of second, third, and fourth-order moments for the passive detection of transient signals in both simulated Gaussian noise and measured noise. The measured noise was recorded by a vertical array located near the San Diego, CA, harbor and is dominated at low frequencies by ship-generated noise. The detectors assume neither noise nor signal stationarity and can use single or multiple channels of data. Simulation results indicate that the fourth-order moment detector often performs better than the energy detector in the correlated measured noise, with increasing channel contributions to the moment function, resulting in increased gain. The results in simulated Gaussian noise likewise favor the fourth-order moment detector, at least for the signals with significant fourth-order moments, but the ability of the higher order detector to discriminate against correlated noise is evident. Analysis over a 30-min segment of the measured noise with selected signals demonstrates that fourth-order detection gains can be reliably expected as the noise statistics change. View full abstract»

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  • Model-based dynamic positioning of underwater robotic vehicles: theory and experiment

    Page(s): 169 - 186
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB) |  | HTML iconHTML  

    This paper addresses the trajectory tracking problem for the low-speed maneuvering of fully actuated underwater vehicles. It is organized as follows. First, a brief review of previously reported control studies and plant models is presented. Second, an experimentally validated plant model for The Johns Hopkins University Remotely Operated Underwater Vehicle (JHUROV) is reviewed. Third, the stability of linear proportional-derivative (PD) control and a family of fixed and adaptive model-based controllers is examined analytically and demonstrated with numerical simulations. Finally, we report results from experimental trials comparing the performance of these controllers over a wide range of operating conditions. The experimental results corroborate the analytical predictions that the model-based controllers outperform PD control over a wide range of operating conditions. The exactly linearizing model-based controller is outperformed by its nonexactly linearizing counterpart. The adaptive controllers are shown to provide reasonable online plant parameter estimates, as well as velocity and position tracking consistent with theoretical predictions-providing good velocity tracking and, with the appropriate parameter update law, position tracking. The effects of reference trajectory, "bad" model parameters, feedback gains, adaptation gains, and thruster saturation are experimentally evaluated. To the best of our knowledge, this is the first reported comparative experimental study of this class of model-based controllers for underwater vehicles. View full abstract»

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  • Special issue on capturing environmental uncertainty in sonar performance

    Page(s): 187 - 188
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  • Special issue on synthetic aperture radar imaging of the ocean surface

    Page(s): 189
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  • Quality without compromise [advertisement]

    Page(s): 190
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  • IEEE copyright form

    Page(s): 191 - 192
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  • IEEE Oceanic Engineering Society Information

    Page(s): c3
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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