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Date 16-18 Sept. 1981

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Displaying Results 1 - 25 of 252
  • [Front cover and table of contents]

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    Freely Available from IEEE
  • [Back cover]

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    Freely Available from IEEE
  • Long-Baseline Deep Ocean Acoustic Tracking and Telemetry System

    Page(s): 1 - 8
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    A portable, long-baseline acoustic tracking system incorporating an acoustic data telemetry link has been developed for deep ocean applications. The system is capable of tracking a surface ship and a submerged object with respect to a bottom-mounted transponder array to an accuracy of better than 10 m. Position updates of the ship and object along with data from the object are obtained every 15 to 20 s. The acoustic communication range of the system is 10 km, which permits tracking of the surface ship in an area of approximately 150 square kilometers in water with a depth of 6 km. This paper describes the general characteristics of the system, including the components, tracking and surveying methods, tracking accuracy, and the results of field tests. View full abstract»

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  • CATEM, A Coherent Target and Environment Model for Sonar Analysis

    Page(s): 9 - 15
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    Major limitations exist in using conventional sonar analysis techniques to predict system performance. Insensitivity of these analysis procedures to signal phase, time delay and spatial effects may be of major concern. The Coherent Acoustic Target and Environment Model (CATEM) is designed to efficiently and accurately predict system performance. The model processes, in a digital manner, the signals that are seen by a sonar located on a moving platform. Program architecture and methods used there- in to simulate the signals that emanate from different acoustic sources are discussed. Examples of the simulated sonar system outputs are given that can be compared to actual system performance. View full abstract»

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  • Time-Domain Theory Results in a Compact Scanning Sonar

    Page(s): 16 - 20
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    A compact within-pulse sector scanning sonar which is based on a time-domain approach and hence differs from conventional modulation scanning systems is described. A 32-input non-uniform time-delay-and-integrate charge coupled device has been designed and fabricated to implement the system. Experimental results are presented for a 500 KHz sonar scanning a 1 beam over a 30° sector at a scanning rate of 8 KHz. View full abstract»

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  • Moving Source/Receiver Underwater Acoustic Tomography

    Page(s): 21 - 25
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    Remote sensing of the interior ocean environment by acoustic signals promises to be a cost effective approach to obtaining high resolution measurements over large areas. In this paper, an approach to remote sensing the interior sound speed of the ocean using historical sound speed data, spatially sparse sampling of sound speed at points within the ocean valume, and acoustic measurements is described. The approach is based on the technology developed in the latter 1970's to produce 3-dimensional images of portions of the human body for use in medical diagnosis, known as Computer Aided Tomography. A recent paper by Munk and Wunsch [1.] describes a system using moored acoustic sources and receivers for remote sensing the ocean interior. Since the acoustic signals respond to sound speed, the result of the tomographic procedure is an estimate of the sound speed field. This paper presents specific results for remote sensing a vertical slice of the ocean sound speed field. The ocean sound speed field is a three-dimensional time dependent process with fluctuations on space and time scales of many different orders of magnitude. There are very intense processes which produce fluctuations equal to 1% of the nominal sound speed over time scales of tens of days, horizontal space scales of 100 kilometers, and vertical space scales of one kilometer. These intense oceanographic processes can be resolved spatially by systems with horizontal resolution of tens of kilometers and vertical resolution of hundreds of meters. Since the processes change on time scales of tens of days, the measurement procedure can occur over a period of days to produce a single image valid for the entire time period. The remote sensing system must provide estimates which are sensitive to fluctuations in sound speed of 1% of the nominal sound speed. The tomographic estimate is based on historical sound speed data, spatially sparse samples of sound speed, and acoustic measurements. The acoustic measurements - - are derived from broad band transmissions which resolve the acoustic multi-paths between source and receiver. The path travel times, amplitudes, and arrival angles contain information related to the ocean sound speed field. In a vertical slice of the ocean along a line connecting source and receiver, at each range there is a different set of ray paths connecting the source and receiver.The rich variety of ray path structures obtained when the range varies provides a means of resolving small spatial variations of the sound speed field. A number of tomographic inversion techniques can be applied. The discrete time Kalman filter appears to be the most appropriate technique. The results of a numerical experiment show that moving source/receiver tomography is feasible, can provide a horizontal spatial resolution on the order of tens of kilometers and is sensitive to sound speed fluctuations of 10-3 times the nominal sound speed in a vertical slice of the ocean. View full abstract»

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  • The Parabolic Equation Method Applied to an Ocean Duct with a Parabolic Index of Refraction Squared

    Page(s): 26 - 30
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    The parabolic equation (PE) method is a range dependent, wave theoretic model. Both the modeling and the numerical limitations of this method are investigated for a range independent ocean duct with parabolic index of refraction squared implemented using the split step Fourier algorithm. Equations are given for determining the minimum number of depth sampling points, and the error due to range step size. The error due to range step size is dependent on the sound speed gradient, frequency, and the cube of the range increment. With an appropriate range step size and number of depth sampling points, the numerical errors are negligible. However, in multi-mode propagation, phase and group velocity errors cause the resulting range-versus-loss curve to be shifted in range. This is due to modeling limitations in the parabolic equation which cannot be changed without further theoretical work. View full abstract»

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  • Predicted Performance of a Heterodyne Detector with a Fiber Optic Coil Hydrophone

    Page(s): 31 - 34
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    In recent years, much attention has been focused on the application of fiber optics to underwater acoustic detection. In this regard, a hydrophone may be constructed of coiled optical fiber. Ultimately, it would be desirable to have only fiber optic elements and cables in the wet end of a towed array system. However, lead fibers are also susceptible to acoustic modulation, introducing grave ambiguities in the detection process. In this paper, a hetero-dyne detection system, devised at General Electric, which will eliminate the problems associated with stray signals induced in the lead fibers, is analyzed for use in a towed array. View full abstract»

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  • A Tracking and Telemetry System for Severe Multipath Acoustic Channels

    Page(s): 35 - 39
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    Underwater telemetry systems require special design when they are to be used in severe multipath acoustic channels. This paper describes a modulation/signal processing method, called Spaced-Frequency-Shift Keying (SFSK), that effectively penetrates such channels. SFSK includes features for reliable message validation, message identification, transfer of binary telemetry, and operation over Doppler ranges commensurate with maximum-speed underwater vehicles. Although SFSK was developed for the specific purpose of underwater vehicle tracking, it is easily adaptable to a wide range of underwater communications applications. View full abstract»

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  • The Multichannel Acoustic Telemetry System

    Page(s): 40 - 42
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    An acoustic system to measure a descent velocity of a self-contained instrument package is described in this paper. The system Is also capable of transmitting two additional time variables. The velocity measurement is based on the Doppler frequency shift of an acoustic signal, while the two other channels use frequency modulated carriers. Errors introduced by heave of a receiving hydrophone is compensated by an integrated signal derived from an accelerometer placed in the hydrophone housing. The results from sea trials are presented and the system performance is evaluated. View full abstract»

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  • A Versatile Multi-Channel Data Acquisition System for Seismic and Acoustic Applications

    Page(s): 43 - 47
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    Versatility and reliability were key factors in the the design of a minicomputer based digital data acquisition system. Used both at sea and on the polar ice with excellent results, it has been adapted to tasks ranging from at-sea continuous seismic profiling to low level acoustic transmission experiments. Of particular interest is a floating point amplifier utilizing a unique gain switching method developed to permit simultaneous sampling of multiple channels up to a 1 kHz signal hand- width. Other features include continuous or intermittent recording in a time demultiplexed format, floating point normalization hardware, sampling times traceable to absolute time, and real-time video display of selected data channels. The system can be used for analysis and processing when not in the acquisition mode. View full abstract»

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  • A Survey of Acoustic Telemetry

    Page(s): 48 - 54
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    Acoustic telemetry from underwater submersibles and sensors has been pursued ever since it was recognized that the ocean could support signal transmission. While it has been evident that some form of communication is possible, the ocean has proved to be a distressingly difficult medium in which to achieve high data rates. High data rate transmission requires a wide bandwidth which is severely constrained in the ocean because of the absorption of high frequency energy. Moreover, the ocean is a very reverberant environment with both time and frequency spreading of signals; this further limits data transmission rates. The net effect of the bandwidth and reverberation constraints has led to either acoustic telemetry systems with low data rates or to the use of tethered systems. Over the years, various forms of acoustic communication systems have been developed. These have included direct AM and SSB for under- water telephones, EM for sensor data, FSK and DPSK for digital data, and parametric sonars for narrow beam systems. As offshore operations have increased, several other systems have been proposed and/or built to respond to particular needs. In this paper, we review the underwater channel and the limitations that it imposes upon acoustic telemetry systems. We then survey some of the systems that have been built (excluding military systems) and indicate how they use various communication system principles to overcome these limitations. View full abstract»

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  • DATS - A Digital Acoustic Telemetry System for Underwater Communications

    Page(s): 55 - 60
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    High data rate acoustic telemetry for underwater communications is limited by both the available bandwidth imposed by high frequency absorption and the range and Doppler spreading of the underwater channel. These limitations can be combatted by the use of spread channel communication techniques. Application of these techniques, however, has been limited by the space and power limitations required to implement the appropriate coding, waveform synthesis and modulation that are encountered in under- water environments. The availability of microprocessors and low power LSI circuits has changed the situation significantly so that now an extensive amount of signal processing can be packaged on remote underwater vehicles and sensors. During the last two years, M.I.T. and W.H.O.I, have jointly developed a digital acoustic telemetry system, DATS. The DATS system has been developed to characterize and test the data transmission properties of underwater channels using the capabilities made available by advances in solid state technology. The design of the DATS and its use is described in the paper. View full abstract»

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  • MFSK--The Basis for Robust Acoustical Communications

    Page(s): 61 - 66
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    Subsea acoustic control and communications systems based on FSK modulation have been used in the offshore industry for the past few years. Prerequisites for reliable link operation included frequency and spatial diversity, signal coding, and channel equalization. These prerequisites limited previous systems to very low data rates. In this paper, an acoustic modem capable of an order of magnitude increase in data rates is discussed. This improved acoustic modem achieves higher data rates by simultaneous transmission of multiple tones using FSK modulation. While not new, until now this technique has been impractical because of the hardware constraints imposed by multitone signal processing. Rapid advancements in the areas of charge transfer devices and Fast Fourier Transform processors removed these constraints. Tradeoffs discussed in this paper include the various signal-processing alternatives available and the use of error correcting or detecting codes to reduce the system undetected-error rate to acceptable values. View full abstract»

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  • Applications of the MFSK Acoustic Communications System

    Page(s): 67 - 71
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    Requirements for control and data acquisition from remote subsea wellheads are expected to grow during the 1980s. In this paper, the implementation of an 'underwater acoustic approach is developed, together with the companion problems-achieving hardware reliability and low power consumption. A companion paper, "MFSK-The Basis for Robust Acoustical Communications," outlines a technique for achieving reliable acoustical communications. The goals that were set included long-range communications, up to 10 kiloyards; dependable communications, 99-percent correct messages under worst-case noise and multipath; secure communications, probability of an undetected error of less than 1 by 10 ; high reliability, 95-percent probability of successful operation for 5 years; and operation from a practical-sized battery pack. Using acoustical communications hardware together with a microprocessor, a theme of total subsea control capability is developed. Practical examples include sequential hydraulic control with acoustical data acquisition and backup control, as well as electro-hydraulic multiplex BOP control with acoustic backup. View full abstract»

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  • Benthic 4800 BITS/S Acoustic Telemetry

    Page(s): 72
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    In June, 1981, continuous 4800 bits/s digital data was acoustically telemetered in 15,000-foot deep water from a near-bottom instrumentation package to a surface platform. As the platform drifted from overhead to an offset angle greater than 45° from the vertical, over 1.0×107 bits of pseudo-random digital data were transmitted with a total of 10 received errors, yielding an average bit error rate of 1×10-6. For the same experimental conditions 2.6×106 bits of 1200 bits/s data were transmitted downward without making a single error. In addition to the digital data, voice, pings, tones and slow-scan television were transmitted. All transmissions were at a transducer input power level of 33 Watts and were between 8 and 14 kilohertz. The modulation technique used was dual independent sideband with an injected pilot tone to provide for Doppler correction. Within each independent sideband, the pseudo-random digital data was transmitted using quad differential phase shift keying and slow-scan television data was transmitted using non-orthogonal frequency shift keying. These results are the culmination of a 5-year effort to determine the limitations on high data rate telemetry imposed by the near vertical (~0°-45°) acoustic channel. The pop-up instrumentation package BUMP (Benthic Untethered Multipurpose Platform) was used throughout these tests as an acoustic source and receiver. The main features of this package and accomplishments of earlier tests will be discussed along with the aforementioned results. View full abstract»

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  • Identification of Missions for Potential Unmanned Untethered Submersible Systems

    Page(s): 73 - 77
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    This paper's objective Is to Identify near and far-term underwater/Ice missions for which potential unmanned, untethered submersible (UUS) systems may become prime candidates. Its introduction includes a review of subjects to be considered and the rationale for procedures followed. Overviews of possible UUS systems and their general potential for serving underwater/ice missions are presented. An analysis of anticipated system capabilities, as both enhanced and limited by eliminating tethers, provides the basis for identifying the missions of interest. Concluding comments reflect on the paper's perspectIve. View full abstract»

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  • Torpedo Technology in the 1980's

    Page(s): 78 - 82
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    New technology provides the opportunity for significant advances in undersea vehicles. Advances in artificial intelligence will permit vehicles to "learn" from measuring their environment and be able to distinguish desired targets from fish, rocks, boundaries, etc. Very high speed integrated circuitry (VHSIC) will package this capability compactly. Lithium type batteries and high speed motors with new magnetic materials or high energy metallic fuels with turbines or engines combined with computer designed thrust producers in filament wound or composite shells promise high performance systems. View full abstract»

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  • Computer Systems for Autonomous Vehicles

    Page(s): 83 - 87
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    The advent of the microprocessor has permitted a substantial amount of computing power to be placed in underwater automata for inspections, work, and other tasks under conditions where tethers are not desirable. Hardware costs are low and power consumption minimal. This paper examines the impact of the microprocessor computer on the autonomous vehicle. The trend toward distributed processing, and the increasing memory size, and the consequent impact on mission capabilities, communication, navigation and control are reviewed. Software design guides the reliability and effectiveness of the hardware, and demands a major portion of development effort. Progress in user oriented languages, software system design, and in flexibility between system elements is described. View full abstract»

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  • Dynamics and Hydrodynamics of Ocean Vehicles

    Page(s): 88 - 91
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    A state-of-the-art review of the dynamics of ocean vehicles is presented. A review of the six-degree-of-freedom nonlinear equations of motion acquaints the reader with the number, type and importance of the terms for various maneuvers. Application of these equations about the linearized equilibrium condition, Uο= constant, which decouples the horizontal and vertical plane equations, is discussed from both a vehicle design and control system point of view. Application of any set of equations of motion requires knowledge of the values for the hydrodynamic coefficients. The preferred method for obtaining these coefficients during the vehicle design process is to predict the coefficients from the geometry of the vehicle without resorting to tunnel testing. Present capability for the prediction of linear and nonlinear hydrodynamic coefficients is discussed,along with examples that demonstrate the current accuracy of prediction methods. View full abstract»

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  • SPURV II-An Unmanned, Free-Swimming Submersible Developed for Oceanographic Research

    Page(s): 92 - 98
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    SPURV II, a Self-Propelled Underwater Research Vehicle, is the latest in a series of such vehicles developed by the Applied Physics Laboratory of the University of Washington for use in its oceanographic research programs. Previous vehicles include several earlier versions of SPURV for deep ocean work (to 3000 meters) and UARS (Unmanned Arctic Research Submersible), a vehicle for under-ice re- search. SPURV II is a modification of one of the earlier SPURV systems and was developed specifically to improve the platform stability and increase the spatial frequency bandwidths of the oceanographic sensors. It has a shallower depth capability (1500 meters) than previous SPURVs but has increased performance in endurance and speed, a more sophisticated guidance and control system, and a greatly expanded sensor suite and associated recording system. In particular the new sensors include the measurement of temperature, conductivity and 3-axis velocity with recording frequencies of 90 Hz and the recording of hot and cold platinum film sensors at 900 Hz to measure the temperature and velocity fields associated with oceanic turbulence. This paper provides a brief description of SPURV II and its surface support equipment which includes, in addition to the vehicle handling equipment, a computer based tracking and command system and a separate larger computer system for data readout and analysis. View full abstract»

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  • Epaulard: - Deep Bottom Surveys Now with Acoustic Remote Controlled Vehicle - First Operational Experience

    Page(s): 99 - 103
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    Designed in 1976, built in 77-78, tested at sea in 79-80 and now in operation on nodule fields in the Pacific Ocean, EPAULARD is the first acoustic remote controlled free swimming vehicule for deep ocean bottom photographic and bathymetric surveys. This paper describes briefly the system and presents at sea operational results including great depths (-5 300 meters). View full abstract»

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  • The UNH EAVE-East Vehicle

    Page(s): 104 - 108
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    EAVE (Experimental Autonomous Vehicle) is a system for the development of technology for untethered, unmanned underwater vehicles. The central focus of this program is the use of a microprocessor system dedicated to mission performance and to the control of distributed processors. The slave processors interface with the vehicle environment, and activate appropriate responses. This paper describes the early development of EAVE as an autonomous pipeline follower. It then discusses the on-going effort to perform three-dimensional structural inspection missions. The objectives of system development, the integration of key technologies, the evaluation of the multiprocessor computer as well as the hardware and software configurations are reviewed. View full abstract»

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  • Robot II, A Small Unmanned Untethered Underwater Vehicle

    Page(s): 109 - 112
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    A small unmanned, untethered submarine vehicle has been designed and is nearing completion. It has a speed of three knots for about four hours with a design depth of 300 feet. The main mission of the vehicle is as aplatform for side-scan sonar. The vehicle has a cylindrical pressure hull fabricated in aluminum with an external skin to provide a low-drag shape. The submarine operates autonomously under the supervision of a Z-80-based microcomputer system which includes a digital autopilot, a ballast control system, and an acoustic command link. The autopilot controls four stabilizers independently, receiving information from a set of very low-cost sensors. The system is capable of carrying out a pre-selected series of stored concise commands as well as responding to changes received from the shore-based acoustic communication system. View full abstract»

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  • Tradeoff Studies for the Unmanned Free Swimming Submersible (UFSS) Vehicle

    Page(s): 113 - 117
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    In the early stages of the design of the UFSS vehicle decisions had to be made between fundamentally different solutions to three basic problems: the energy source, the propulsion method, and the hull shape, which determined drag. Accordingly a series of tradeoff studies was undertaken which considered the various alternatives in the light of the desired performance levels of the vehicle and the constraints of both time and money placed on the entire effort. Possible energy sources included fuel cells, various battery systems, dynamic converters, and even a nuclear heat converter. Two different hull configurations were considered for which drag differed by a factor of three. Propulsion techniques included pump jets, a method based on the Coanda effect, and a conventional propeller coupled to a variety of prime movers. In the course of the work a great deal of quantitative information was obtained both on the technical characteristics of the various systems and on the likely costs of those which needed further development. View full abstract»

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