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Oceanic Engineering, IEEE Journal of

Issue 4 • Date Oct. 2002

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Displaying Results 1 - 15 of 15
  • Editor's corner

    Page(s): 773
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    Freely Available from IEEE
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  • Author index

    Page(s): 877 - 880
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  • Subject index

    Page(s): 880 - 890
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  • Theoretical accuracy of synthetic aperture sonar micronavigation using a displaced phase-center antenna

    Page(s): 780 - 789
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (993 KB) |  | HTML iconHTML  

    The Cramer-Rao lower bounds on the cross-track translation and rotation of a displaced phase-center antenna (DPCA) in the slant range plane between two successive pings (known as DPCA sway and yaw in what follows) are computed, assuming statistically homogeneous backscatter. These bounds are validated using experimental data from a 118-182-kHz sonar, showing an accuracy of the order of 20 microns on the ping-to-ping cross-track displacements. Next, the accuracy required on the DPCA sway and yaw in order to achieve a given synthetic aperture sonar (SAS) beampattern specification, specified by the expected SAS array gain, is computed as a function of the number P of pings in the SAS. Higher accuracy is required when P increases to counter the accumulation of errors during the integration of the elementary ping-to-ping estimates: the standard deviation must decrease as P-12/ for the DPCA sway and P-32/ for the yaw. Finally, by combining the above results, the lower bounds on DPCA micronavigation accuracy are established. These bounds set an upper limit to the SAS length achievable in practice. The maximum gain Q in cross-range resolution achievable by a DPCA micronavigated SAS is computed as a function of the key SAS parameters. These theoretical predictions are compared with simulations and experimental results. View full abstract»

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  • FFT-based joint bearing estimation

    Page(s): 774 - 779
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (558 KB) |  | HTML iconHTML  

    The least-squares estimate for the joint estimation of M directions-of-arrival in an array-processing scenario is rederived in a way that makes explicit use of the discrete Fourier transform. It is shown that the M-dimensional search algorithm can be made orders of magnitude faster than the traditional search algorithm. This new approach is compared via simulation with conventional narrowband beamforming. View full abstract»

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  • Measurement of sound transmission and signal gain in the complex Strait of Korea

    Page(s): 841 - 852
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (885 KB)  

    The experiment, The Acoustic Characterization Test III, was conducted in the oceanographically complex Strait of Korea to accurately measure the sound transmission under known environmental conditions. Geoacoustic profiles derived from geophysical measurements, measured bathymetry, and sound-speed profiles were the basis for range dependent parabolic equation (PE) calculations. Agreement between measured and calculated transmission loss was obtained with an attenuation profile in the near water-sediment interface layer with a dependence on frequency to the 1.8 power consistent with measurements in other sand-silt areas. Since the environment was oceanographically complex and the shipping noise levels were high, the coherency of the sound transmission was estimated using relative signal gain (RSG). RSG was taken as the difference between the gain calculated with PE and measured with the array and at longer ranges and higher frequencies was found to be approximately -2 dB with a signal gain coefficient of variation of 5%. This RSG degradation, attributed to the random signal phase fluctuations resulting from scattering from the surfaces and volume of the waveguide, yielded using a Gaussian coherence function a spatial coherence length of 30λ @ 400 Hz-40 km. In addition, high resolution imaging of five targets with two bottom mounted arrays illustrate the achievable performance of low-to-mid frequency active sonar in this environment. View full abstract»

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  • Novel physical interpretations of K-distributed reverberation

    Page(s): 800 - 813
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (594 KB) |  | HTML iconHTML  

    Interest in describing and modeling envelope distributions of sea-floor backscatter has increased recently, particularly with regard to high-resolution active sonar systems. Sea-floor scattering that results in heavy-tailed-matched-filter-envelope probability distribution functions (i.e., non-Rayleigh distributions exemplified by the K, Weibull, Rayleigh mixture, or log-normal distributions) is often the limiting factor in the performance of these types of sonar systems and in this context is referred to as reverberation or acoustic clutter analogous to radar clutter. Modeling of reverberation has traditionally entailed fitting various candidate distributions to time samples of the envelope of the scattered sonar (or radar) returns. This type of descriptive analysis and the asymptotic (infinite number of scatterers) analysis defining the K-distribution yield little insight into the environmental mechanisms responsible for heavy-tailed distributions (e.g., distributions and, clustering of discrete scatterers, patchiness in geo-acoustic properties, scattering strength of scatterers, etc.) and do not allow evaluation of the effect of changing sonar system parameters such as bandwidth and beamwidth. In contrast, we derive the envelope distribution for the scattered returns starting from simple physical descriptions of the environment with a finite number of scatterers. It is shown that plausible descriptions of the environment can lead to K-distributed reverberation. This result explains, at least partially, the success of the K-distribution in the modeling of radar clutter and sonar reverberation at a variety of frequencies and scales. The finite-number-of-scatterers model is then used to predict how the shape parameter of the K-distribution will change as the beamwidth of a towed-array receiver is varied. Analysis of reverberation data from a low-frequency (450-700 Hz) active sonar system illustrates that, within our ability to estimate it, the shape parameter of the K-distribution is proportional to the beamwidth of the towed-array receiver, a result important for sonar simulation and performance prediction models. These results should prove useful in developing methods for modeling, predicting and mitigating reverberation on high-resolution sonar systems. View full abstract»

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  • A remark on "Nonlinear output feedback control of underwater vehicle propellers using feedback form estimated axial flow velocity"'

    Page(s): 873 - 875
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB) |  | HTML iconHTML  

    For original paper see T.I.Fossen and M.Blanke, ibid., vol.25, pp.241-55 (2000). In the work presented by Fossen and Blanke, a nonlinear observer for estimation of propeller axial flow velocity for UUVs was introduced. The proof of the convergence behavior of the observer was carried out with a Lyapunov analysis. In this technical communication, such an analysis was also briefly compared with the so-called contraction analysis. This communication goes further into the details of the comparison by proving - through a link between contracting and globally exponentially stable (GES) systems - that the observer is both contracting and GES, showing thus that contraction analysis might be regarded as an interesting alternative to Lyapunov-based designs. Furthermore, some qualitative advantages gained when using contraction analysis are given. View full abstract»

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  • 3-D underwater object recognition

    Page(s): 814 - 829
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    In this paper, we propose an automatic supervised classification of objects lying on the sea floor or buried in sediment layers. This pattern recognition provides a way to distinguish natural and manufactured objects and then should be helpful to detect mine, pipe-line, or wreckage. Proposed methods combine different techniques: pattern information extraction, relevant parameter search, and supervised classifier. Parameters are automatically selected using a principal component analysis to reduce misclassification rate and to simplify classifier structure. Performances of different parameters (two-dimensional and three-dimensional) are compared and discussed from testing on synthetic and real data bases. View full abstract»

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  • A seamless system for the collection and cultivation of extremophiles from deep-ocean hydrothermal vents

    Page(s): 862 - 869
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1445 KB) |  | HTML iconHTML  

    Pele's Pit is a 300-m-deep pit crater whose summit rises to a depth of 1000 m on the Loihi submarine volcano 34 km south of the island of Hawaii. Hydrothermal vents with water temperatures up to 198°C have been observed at the basal edge of the pit. We fabricated a "seamless" system comprising submersible-mounted samplers, a helium-activated sample transfer system, and a series of 1-l Teflon-lined stainless-steel bioreactors that maintain ambient temperature and pressure in hydrothermal vent fluids collected from hydrothermal vents in the pit crater. The bioreactors can sustain pressures to 150 atm. and temperatures over 165°C. The system was deployed during October 2001 Pisces V submersible operations on Pele's Pit during which the maximum vent water temperature measured was 90°C. View full abstract»

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  • Design of sparse linear arrays by Monte Carlo importance sampling

    Page(s): 790 - 799
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (677 KB) |  | HTML iconHTML  

    The formation of acoustic images in real-time requires an enormous computational burden. To reduce this demand the use of sparse arrays for beamforming is mandated. The design of these arrays for adequate mainlobe width and low sidelobe level is a difficult nonlinear optimization problem. A new approach to the joint optimization of sensor placement and shading weights is discussed. Based on the concept of importance sampling an optimization method is presented and some examples given to illustrate its effectiveness. View full abstract»

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  • Coherent reflection of acoustic plane wave from a rough seabed, with a random sediment layer overlying an elastic basement

    Page(s): 853 - 861
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    The problem of coherent reflection of an acoustic plane wave from a rough seabed with a randomly inhomogeneous sediment layer overlying a uniform elastic basement is considered in this analysis. The randomness of the sound field is attributable to the roughness of the seabed and the sound-speed perturbation in the sediment layer, resulting in a joint rough surface and volume scattering problem. An approach based upon perturbation theory, combined with a derived Green's function for a slab bounded above and below by a fluid and an elastic half-space, respectively, is employed to obtain an analytic solution for the coherent field in the sediment layer. Furthermore, a boundary perturbation theory developed by Kuperman and Schmidt (1989) is applied to treat the problem of rough surface scattering. A linear system is then established to facilitate the computation of the coherent reflection field. The coherent reflection coefficients for various surface roughness, sediment randomness, frequency, sediment thickness, and basement elasticity have been generated numerically and analyzed. It was found that the higher/larger size of surface and/or medium randomness, frequency, thickness, and shear-wave speed, the lower the coherent reflection. Physical interpretations of the various results are provided. View full abstract»

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  • False-bottom acoustic echo in mid water? A note on how to evaluate and prevent the interference

    Page(s): 870 - 872
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (374 KB) |  | HTML iconHTML  

    The 2000 hydroacoustic survey of Lake Matano, Sulawesi is used to illustrate the mechanism of formation of an artificial, but acoustically-observed density layer in the midst of the water column. Such a spurious signal resembling the true acoustic target can be formed under certain combinations of the lake morphology and the echosounder settings by way of recording the residual echo from the previous ping during the subsequent ping-recording interval. The. generic physical mechanism of the phenomenon is described and the necessary conditions for its formation stated. The echosounder settings sufficient to prevent the interference during the field surveys are suggested, and their application illustrated with an example. The phenomenon described is explained by the physics of sound propagation and hence, the algorithms here developed apply to other water bodies and hydroacoustic equipment. View full abstract»

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  • Estimation of hydrodynamic coefficients for an AUV using nonlinear observers

    Page(s): 830 - 840
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1081 KB) |  | HTML iconHTML  

    Hydrodynamic coefficients strongly affect the dynamic performance of an autonomous underwater vehicle. Although these coefficients are generally obtained experimentally such as through the planar-motion-mechanism (PMM) test, the measured values are not completely reliable because of experimental difficulties and errors involved. Another approach by which these coefficients can be obtained is the observer method, in which a model-based estimation algorithm predicts the coefficients. In this paper, the hydrodynamic coefficients are estimated using two nonlinear observers - a sliding mode observer and an extended Kalman filter. Their performances are evaluated by comparing the estimated coefficients obtained from the two observer methods with the values as determined from the PMM test. By using the estimated coefficients, a sliding mode controller is constructed for the diving and steering maneuver. It is demonstrated that the controller with the estimated values maintains the desired depth and path with sufficient accuracy. 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.

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