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OCEANS '94. 'Oceans Engineering for Today's Technology and Tomorrow's Preservation.' Proceedings

Date 13-16 Sep 1994

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  • Shipborne measurement of surface current fields by HF radar

    Publication Year: 1994 , Page(s): III/23 - III/27 vol.3
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    HF radar is a remote sensing technique for measuring surface currents and ocean wave directional spectra. This paper describes the extension of a land based system to enable surface current measurements from a slowly sailing ship. To compensate for the ship's motion, the Global Positioning System (GPS) has been used. Due to additional error sources compared to the land based system, the accuracy of measured currents is slightly reduced from 2 to 5 cm/s to 3 to 10 cm/s View full abstract»

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  • Influence of mooring dynamics on current records

    Publication Year: 1994 , Page(s): III/28 - III/33 vol.3
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    In order to evaluate some tidal records made during the GASTOM 90 oceanographic mission, a dynamic finite element simulation is used to study the behaviour of mooring lines. A theoretical approach, mainly a non-dimensional analysis and parametric study based on a simplified mesh, allows the authors to identify the relevant parameters for the modelisation and the accurate environmental constraints used for the numerical forcing simulations. The final results allow them to quantify, a posteriori, the expected M2 tidal signal affecting ocean on the measured area View full abstract»

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  • SWAFS: shallow water analysis and forecast system

    Publication Year: 1994 , Page(s): III/82 - III/87 vol.3
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    A numerical ocean forecast system has been assembled and applied to several semi-enclosed basins. The modelling system includes a numerical model of ocean circulation, a data assimilation scheme, real-time meteorological forecasts, and data bases of in situ temperature observations and sea-surface temperatures inferred from satellites. Forecast results for the Red Sea are shown View full abstract»

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  • Lagrangian ambient noise drifter

    Publication Year: 1994 , Page(s): III/34 - III/39 vol.3
    Cited by:  Papers (2)
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    The Defence Research Establishment Atlantic has carried out an experiment to study the relationship between ambient noise and oceanographic features in regions of pronounced oceanic currents, such as the Gulf Stream or its eddies, using a field of purpose built, long life drifting buoys developed and maintained at sea by Seimac Limited, of Dartmouth, Canada. These Lagrangian Ambient Noise Drifters (LANDs) comprise a drogued free floating buoy which employs telemetry over ARGOS satellites to report hourly measurements of the underwater ambient noise spectrum, as well as the surface wave energy spectrum, wind speed and direction, Global Positioning System geographic position, and water temperature at the sea surface and at the hydrophone. This paper presents the various aspects of the design of the LAND buoys, with particular emphasis on the techniques for measuring and processing the ambient noise and surface wave height data. Comparative data for these parameters are presented View full abstract»

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  • Multifrequency acoustic imaging of suspended sediment processes

    Publication Year: 1994 , Page(s): III/263 - III/268 vol.3
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    Multifrequency acoustic backscattering has been used to obtain images of suspended sediments. A number of results are presented which show how the technology can be used to examine the broad picture on a tidal scale, or focus on detailed particular events which only last a period of seconds View full abstract»

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  • Hydroacoustical experiments for determination of sediment parameters

    Publication Year: 1994 , Page(s): III/207 - III/212 vol.3
    Cited by:  Papers (2)
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    Three different kinds of hydroacoustical experiments conducted in Kalmarsund in the Baltic are described: (1) excitation with a slowly moving monofrequency source for transmission loss measurements and modal structure analysis, (2) excitation of transient waves using explosive charges, (3) excitation with a frequency sweep for analysis of transmission loss as function of frequency. The experiments are analysed within the framework of a laterally homogeneous model, treating the seabed as a layered elastic solid. Geoacoustic modeling and inversion for medium parameters is performed using genetic algorithms View full abstract»

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  • Depth control of an unmanned underwater vehicle using neural networks

    Publication Year: 1994 , Page(s): III/121 - III/125 vol.3
    Cited by:  Papers (2)
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    Artificial neural networks offer an alternative strategy for the non-linear control of unmanned underwater vehicles (UUVs). This paper presents the results of a simulation study into the development of a neural network controller for depth control of a UUV. Results presented compare the performance of the neural controller based on the multilayered perceptron (MLP) chemotaxis training algorithm with proportional-integral-derivative (PID) controller. Results will show that in the presence of noise and change in mass of the vehicle the neural controller out performed the standard PID controller View full abstract»

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  • Structure of operational oceanographic nowcast and forecast systems

    Publication Year: 1994 , Page(s): III/88 - III/92 vol.3
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    Presents in a pedagogical manner some elements leading to operational nowcast and forecast oceanic systems serving navies View full abstract»

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  • Simultaneous use of eulerian and lagrangian currents measured by VHF radars for estimating the horizontal diffusion coefficient in coastal circulation

    Publication Year: 1994 , Page(s): III/40 - III/44 vol.3
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    A VHF radar has been used to locate a drifting transponder for measuring the lagrangian circulation in the coastal zone. It is expected that simultaneous use of several drifters will give an insight into small scale dispersion and diffusion phenomena. The paper describes the radar and transponder system, and outlines the method used to estimate the horizontal diffusion coefficient View full abstract»

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  • Analysis of multibeam echo-sounder signals from the deep seafloor

    Publication Year: 1994 , Page(s): III/213 - III/218 vol.3
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    The new generation low-frequency echo-sounders, covering the full angular range, are also able to record acoustic images comparable to side-scan sonars. Possibilities of using these systems for sea-floor type identification are currently being investigated. Experimental echoes obtained with a 13 kHz multibeam echo-sounder have been collected and processed for a variety of sea-floor types and water depths. The results of two different analysis methods are presented. The backscattering strength of the sea-floor and its angular variations are known to be strongly dependent on the seabed type. They may be obtained as a function of incident angle from the measured levels averaged in narrow tilted beams, after correcting for the insonified area, the refraction by the sound-speed profile and the sea-floor local slopes. The results of this method make clear large differences between the various investigated seabed classes. The spectral features of backscattered time signals have previously been shown to be a useful tool for identification by side-scan sonars. The authors present the first results obtained by this method for deep sea-floor multibeam echoes: notable discrepancies between the spectral parameters corresponding to various seabeds are shown, enhancing the possibility of using such a technique for low-frequency echo-sounders View full abstract»

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  • A new method for acoustic ray tracing

    Publication Year: 1994 , Page(s): III/189 - III/194 vol.3
    Cited by:  Papers (1)
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    The paper describes a new method for acoustic ray tracing. The method is based on the concept of a travelling wavefront, which leads to a new formulation and a simple algorithm for ray tracing. The approach is suitable for arbitrary sound speed profiles which can be approximated by differentiable functions. It does not require linearisation and is particularly convenient for computer simulations. It can be easily generalized to include range-dependent cases in which the sound speed profiles change with the horizontal distance. Several examples are presented to illustrate the usefulness or the method and to assess its accuracy View full abstract»

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  • Multiple agents architecture for intelligent command and control system of AUVs : application to the MARIUS vehicle

    Publication Year: 1994 , Page(s): III/126 - III/131 vol.3
    Cited by:  Papers (6)
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    This paper addresses the problem of intelligent command and control systems for AUVs. It presents a conceptual multiple agents based architecture proposed for the MARIUS prototype vehicle (devoted to coastal survey missions). The paper presents the characteristics of the vehicle system and a synthesis of the functional requirements to be fulfilled; it describes the proposed multiagents architecture for the onboard mission management system, with details on architecture, functionalities and communications capabilities of the agents It describes the mapping of the functional decomposition of the RIMS on this multiple agents architecture View full abstract»

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  • Underwater operations with the “MIR” submersibles in 1990-1994

    Publication Year: 1994 , Page(s): III/154 - III/158 vol.3
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    During the last four years the “MIR-1” and “MIR-2” deep manned submersibles of P.P. Shirshov Institute of Oceanology of Russian Academy of Sciences were used for scientific research as well as for different types of special underwater technical operations. All the expeditions with the “MIR” submersibles were conducted at the international level. In different expeditions of r/v “Akademik Mstislav Keldysh”-support vessel of the “MIR”s-large groups of the scientists from the United States, Canada, Germany, England and other countries participated. A large volume of scientific results was obtained. During the dives different movies were obtained and unique underwater operations were performed View full abstract»

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  • Measurements with a three frequency echo sounder for the detection of suspended matter in a river estuary

    Publication Year: 1994 , Page(s): III/258 - III/262 vol.3
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    Field measurements of backscattered acoustic energy taken with a three frequency echo sounder in an estuary under tidal influences are presented. The vertical and temporal distribution of suspended matter, as well as settling and resuspension effects are analysed and discussed View full abstract»

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  • A nonlinear sliding mode autopilot for unmanned undersea vehicles

    Publication Year: 1994 , Page(s): III/93 - III/98 vol.3
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    A nonlinear sliding mode autopilot has been designed to control the United States Navy, Office of Naval Research (ONR) unmanned undersea vehicles (UUVs). The paper discusses the selection process behind the choice of the sliding mode technique, and the design of the autopilot. This autopilot has been successfully demonstrated at sea and test data are presented. The autopilot has exhibited excellent dynamic control, performing manoeuvres at a range of different speeds View full abstract»

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  • Element level simulation of sonar echo from a moving target in an ocean waveguide

    Publication Year: 1994 , Page(s): III/195 - III/199 vol.3
    Cited by:  Patents (1)
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    The source, receiver and target dynamics in an ocean waveguide have significant effects on the performance of high resolution spatial and temporal processing. In a multipath environment, the motion causes Doppler shifts that are different for different paths. A procedure is developed for element level time series simulation for high frequency sonar returns in a monostatic scenario that includes the effects of source, receiver and target dynamics. The extension to the bistatic case is straight forward. The procedure consists of propagating the signal from the source to the target using ray tracing, projecting the incident field on to the scattered field, and propagating back to the receiver. The source, receiver and target dynamics is taken into consideration during propagation from the source to the target and from target to the receiver. The projection of the incident field onto the scattered field is accomplished using a T-matrix formulation. The modeling procedure is applied to a shallow water ocean waveguide with a rigid sphere as a target. The source, receiver and target motion is confined to a constant depth without loss of generality. The results demonstrate different Doppler shifts for different paths and the received signal exhibit the effect of motion View full abstract»

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  • Vectorial magnetic field of a vessel from the vertical field

    Publication Year: 1994 , Page(s): III/519 - III/521 vol.3
    Cited by:  Patents (1)
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    The easiest and cheapest way to get the magnetic field of a vessel is to measure the vertical component of the field while the vessel moves over an array of vertical magnetic sensors located in a horizontal line (perpendicular to the bow-stern direction) at a particular depth. In order to obtain the vectorial field of the vessel (three-component field) the author has used a mathematical technique based on potential theory, applying it to the data of the vertical field. The technique is easily implemented as software for a microcomputer. It has the advantage of producing exact results (it is not a mathematical model) in a few seconds of processing time, processes data that can be measured by a small number of magnetometers and produces data for any location and oriented in any spatial direction View full abstract»

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  • Review of control methods for underwater vehicles navigation in uncertain environment

    Publication Year: 1994 , Page(s): III/99 - III104 vol.3
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    The paper presents several existing control schemes (adaptive linear control, sliding control mode, neural network control) and their applications to underwater vehicles dynamics control. Through analysis and numerical investigations, the authors compare each of these methods for the same control problem View full abstract»

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  • Evaluation of a deep water wide swath echo sounder for hydrographic surveys

    Publication Year: 1994 , Page(s): III/225 - III/230 vol.3
    Cited by:  Papers (1)
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    Discusses the evaluation of multibeam echo sounders according to the hydrographic survey standards. The French Hydrographic and Oceanographic Service (SHOM) operates two multibeam echo sounders. Both have been accepted as hydrographic (meaning that they meet the hydrographic accuracy standards) for a determined swath width. The first system, a Thomson SINTRA shallow water 20 beams echo sounder called LEMYERMOR, was acquired in 1988. The second system, a SIMRAD EM 12 dual 160 beams deep water echo sounder, was installed and put into service in 1993. Using SHOM experience, this paper mainly describes some “bias” that were observed when evaluating the accuracies of both echo sounders but is mainly based on the sea trials of the EM 12, that were held in 1993 View full abstract»

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  • Data assimilation in quasi-geostrophic ocean models

    Publication Year: 1994 , Page(s): III/337 - III/346 vol.3
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    Performs idealized data assimilation experiments with a nudging technique in a three-layer quasi-geostrophic model to assess the ability of altimeter or float data to control the evolution of a baroclinic flow. In a first series of runs, the authors check the sensitivity of assimilation to nudging parameters in a wind-forced, vertically coherent, reference simulation. In a second batch of experiments, the authors use a vertically strongly decorrelated flow to measure the information content brought by the assimilation of relative vorticity of deep Lagrangian floats View full abstract»

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  • Real time underwater communications

    Publication Year: 1994 , Page(s): III/501 - III/506 vol.3
    Cited by:  Papers (1)
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    Achieving reliable high speed digital communications over an underwater channel is a challenge that many scientists are trying to take up. For various applications such as remote control and data exchange, for example between an autonomous underwater vehicle and a surface vessel, the need is getting more and more important in designing reliable communications systems by means of acoustic waves. The authors focus on a coherent receiver where synchronization (timing recovery and carrier recovery) and equalization are jointly optimized View full abstract»

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  • Short range propagation through an inhomogeneous medium

    Publication Year: 1994 , Page(s): III/172 - III/177 vol.3
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    Inhomogeneity is a characteristic of every real medium, and two types are observed, regular and random. Regular inhomogeneities are produced by spatial variation of the mean characteristics of a medium, for example, velocity variation with temperature, depth and salinity. Random inhomogeneities are produced by deviation from the mean values. In the paper a medium with random inhomogeneities is modelled and ray diagrams illustrate the effect of the magnitude and scale size of the inhomogeneities on the propagation of sound. The sound speed of the medium varies with both range and depth and thus may be described by correlation lengths in both dimensions. The results' presented relate to an existing extreme experimental situation where the propagation range is 170 m with horizontal correlation length of 20 m, vertical correlation length 2 m, and a standard deviation of the local sound speed from the local mean of 0.5 m/s. The modelling results are compared with experimental results View full abstract»

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  • Measurement of sea bed topography and bistatic scattering coefficients with steered frequency source arrays

    Publication Year: 1994 , Page(s): III/200 - III/206 vol.3
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    A method of measuring bottom topography and bistatic scattering coefficients with steered frequency source (SFS) arrays is described and illustrated with modeled reverberation data. SFS array design principles are summarized and methods of analyzing the data to obtain sea bed topography and bistatic scattering coefficients are outlined. The SFS source radiates acoustic energy in a set of narrow vertical beams, each at a different frequency. The source consists of a vertical line array of impulsive charges which are detonated in a time delayed sequential order. This generates a set of nested expanding wave fronts centered at each source element. The observed frequency in each vertical beam is defined by the spacing between the wave fronts measured along a vertical angle of departure from the center of the source. Sea bed topography can be measured with the deployment of a distributed field of azimuthally directive receivers and multistatic SFS source arrays. High resolution topography is calculated from the time/frequency return structure of the bottom scattered reverberation by resolving the bistatic intersection of the SFS vertical source beams and the azimuthal directive receivers. The magnitude of the reverberation, at any given bistatic intersection, is a measure of the bistatic scattering function of the reverberating surface. The strength of the reverberation is related to the bistatic scattering coefficient via the RUMBLE reverberation model of Bucker et al. (1993) View full abstract»

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  • Assimilation of Topex/Poseidon altimeter data into a circulation model of the North Atlantic

    Publication Year: 1994 , Page(s): III/63 - III/68 vol.3
    Cited by:  Papers (1)
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    Assimilation experiments were conducted using the first twelve months of Topex/Poseidon (T/P) altimeter measurements in a multi-layered quasigeostrophic model of the North Atlantic between 20°N and 60°N. These experiments demonstrate the feasibility of using T/P data to control a basin-scale circulation model by means of an assimilation procedure. Moreover, they allow the authors to recreate the 4-dimensional behaviour of the North Atlantic Ocean during the year October 1992-September 1993, and to improve their knowledge and understanding of such circulation patterns View full abstract»

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  • Two-way solution of underwater sound propagation problem in two and three-dimensional environment by pseudodifferential parabolic equation technique

    Publication Year: 1994 , Page(s): III/159 - III/162 vol.3
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    The paper presents some recipes for underwater sound calculations in 2D and 3D ocean models with sound speed and density slowly varying with horizontal coordinates and arbitrary in depth including a nonhomogeneous liquid model of bottom. These recipes are based on the idea of WKB-like factoring and the extensive use of high order Pade approximations for numerical solving of arising pseudodifferential equations. The author starts from the essentially 2D problem of acoustical wave propagation in a three-dimensional liquid waveguide translationally invariable on the y cartesian coordinate without currents View full abstract»

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