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Oceanic Engineering, IEEE Journal of

Issue 1 • Date Jan. 1989

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Displaying Results 1 - 6 of 6
  • Seafloor profiling by a wideband sonar: simulation, frequency-response optimization, and results of a brief sea test

    Publication Year: 1989 , Page(s): 94 - 107
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1363 KB)  

    An ahead-looking probe of some kind, optical or acoustic, is critical when one is attempting seafloor exploration from a mobile platform. A single-frequency, split aperture sonar system can be used for this purpose, but a wideband monopulse sonar offers many advantages. It computes a running estimate of the vertical directional cosine of the source of the echo, and can thus reveal the positions of multiple wave scatterers as long as their echoes can still be time resolved. Theoretical studies of its performance have been made previously, but were directly applicable only to extremely simple seafloor geometries. A new time-domain digital simulation that largely circumvents this limitation has been developed. The simulation also provides a means for testing the theory and optimizing system parameters. The reverberation model does not account for some features of acoustic backscattering such as diffraction, but it is believed to be adequate for the investigation of most signal processing aspects of the sonar system. The theory of the simulation is developed and several examples are presented and discussed. In addition, some preliminary results are presented from a sea test that used the air-sea interface as a surrogate seafloor.<> View full abstract»

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  • Ocean acoustic tomography: estimating the acoustic travel time with phase

    Publication Year: 1989 , Page(s): 108 - 119
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1048 KB)  

    Continuous acoustic transmission (133 Hz, 60-ms resolution) between a bottom-mounted source near Oahu, Hawaii, and a bottom-mounted receiver at 4000-km range near the coast of northern California was recorded to learn how to measure precisely the travel time so that basin-scale fluctuations in the Pacific can be detected. Daily incoherent averages of some of the multipaths exhibited stability during this period. The standard deviation of the travel time of the resolved peaks in the daily incoherent averages is about 30 ms. An acoustic method, based on cross-correlation, is derived to estimate the change in the average acoustic phase (travel time) to a precision of about 0.018 cycles (135 mu s) every 2 min. Travel-time estimates based on the cross-correlator reduce the aberrations due to internal waves by about 19 dB in comparison with CW transmissions. The new travel-time estimator is applied to the measurements to examine some of the fluctuations of the Pacific.<> View full abstract»

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  • A statistical study of acoustic signals backscattered from the sea bottom

    Publication Year: 1989 , Page(s): 84 - 93
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    Backscattering measurements were performed in shallow water on sand, gravel, and clay bottoms. The equipment included a parametric array that emitted pulses of differential frequencies (8 to 40 kHz) with a 3° directivity. The ranges did not exceed 50 m. The grazing angles varied from 4° to 90°. The bottom backscattering strength does not depend on the emitted pulse type (frequency and length). If one fits a Lambert law to the variations of the backscattering strength versus the grazing angle, the value at the origin fluctuates between-15 and-22 dB without any clear effect from the different bottom types. Statistical tests show that under the experimental measurement conditions: (1) the alternative received signal does not generally follow a normal distribution; (2) among five classical distributions in sonar and radar that have been fitted to the detected-integrated signal (exponential, Weibull, chi-2, log-normal, Rice), the best-fitted law is the log-normal; (3) signals backscattered by separated areas of the same bottom can hardly be regarded as stationary and, even less, homogeneous; and (4) with an anisotropic bottom topography the statistical properties depend on the aspect under which this topography is seen View full abstract»

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  • Adaptive processing of microwave sea echo for the suppression of strong reflections from scatterers

    Publication Year: 1989 , Page(s): 76 - 83
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    Adaptive processing of microwave sea echo is proposed for the suppression of strong reflections from scatterers on the ocean surface. An adaptive method using echoes of pulses at different carrier frequencies is also shown to be effective for this purpose. It is noted that nonadaptive processing of the same data does not suppress these reflections. Results obtained by processing coherent microwave backscatter from the ocean surface are presented View full abstract»

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  • Diffraction by a hard truncated wedge and a strip

    Publication Year: 1989 , Page(s): 4 - 16
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    A method of formulating the scattered acoustical field for certain types of hard bodies through the use of well-known exact solutions for the simple semi-infinite wedge and/or corner is presented. The method yields a representation of the total sound field for all frequencies and satisfying all boundary conditions. Relevant hard-wedge solutions for harmonic line sources and for plane waves are reviewed. Such solutions, which are rigorous, represent the total sound field as a superposition of directional line sources and sinks at the wedge vertex. A method of representing multiple scatter from combinations of wedges, allowing the explicit solution of the case of a truncated wedge, is introduced. This method uses the classic self-consistent algorithm for multiple scatter, together with a rigorous representation of vertex-diffracted fields View full abstract»

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  • Acoustic scattering from composite wind-wave surfaces in `bubble-free' regimes

    Publication Year: 1989 , Page(s): 17 - 75
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4192 KB)  

    The problem of underwater acoustic scattering from truly composite wind-wave surfaces under zero-gradient conditions (Δc=0) is examined. Here the dominant small-scale component is postulated to be a soliton surface ensemble, produced by the nonlinear wind-wave interactions and associated with the wind-drift surface layer riding on the underlying, mostly large-scale gravity-capillary component of the composite surface. A general bistatic analysis, based on the Kirchhoff approximation, is presented, which includes arbitrary geometries, beam patterns, and general signals. Both low-frequency O(0.2-1 kHz) and high-frequency O(≳3 kHz) signals are considered, and far-field (Fraunhofer) geometries are assumed. Surface Doppler, including Doppler spread and the modulation effects of the large-scale component, are examined. Both forward-scatter and backscatter regimes are considered in the determination of the scattered field and received wave intensities, scattering cross-sections, and coherency measures of surface scatter. Particular attention is given to the high-frequency cases, with small grazing angles, moderate-to-strong mean surface winds, and essentially bubble-free regimes. Recent empirical data appropriate to these conditions are included, which support the soliton conjecture and illustrate the general results. Both coherent and incoherent scattering are examined, along with relevant surface Doppler data 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