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The following four invited papers in this special issue on acoustic telemetry describe some of the wide variety of its application. A few comments on each paper are included below to introduce the reader to their subject matter. 相似文献
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An overview of matched field methods in ocean acoustics 总被引：4，自引：0，他引：4
Baggeroer A.B. Kuperman W.A. Mikhalevsky P.N. 《Oceanic Engineering, IEEE Journal of》1993,18(4):401-424
A short historical overview of matched-field processing (MFP) is followed by background material in both ocean acoustics and array processing needed for MFP. Specific algorithms involving both quadratic and adaptive methods are then introduced. The results of mismatch studies and several algorithms designed to be relatively robust against mismatch are discussed. The use of simulated MFP for range, depth and bearing location is examined, using data from a towed array that has been tilted to produce an effective vertical aperture. Several experiments using MFP are reviewed. One successfully demonstrated MFP at megameter ranges; this has important consequences for experiments in global tomography. Some unique applications of MFP, including how it can exploit ocean inhomogeneities and make tomographic measurements of environmental parameters, are considered 相似文献
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An extensive refraction profiling program was carried out during the FRAM II experiment (March–May, 1980) in the eastern Arctic Ocean. Two structural areas were covered: north of the ice camp (86°N, 24°W) into the basin of the Pole Abyssal Plain and south onto the flanks of the Morris Jesup Rise. Digital multichannel data on an 800 by 800 m, 24 channel hydrophone array and a single 2-component ocean bottom seismometer (OBS) were recorded for offsets from 2.5 to 100 km. Arrival times, amplitudes and phase velocities of the seismic signals recieved on the hydrophone array were determined using high resolution array processing. From these measurements and the OBS data, preliminary velocity structural models of the crust have been derived. For the purposes of this paper, 2 refraction lines have been analyzed, a 40 km line on a flat region of the Pole Abyssal Plain and an 86 km line on a slightly dipping region taken as the drifting ice camp shoaled on the Morris Jesup Rise. These preliminary analyses yield a sedimentary layer with a gradually increasing velocity 1.5–2 km thick. This cover overlays a crust with a thin layer 2 (< 1 km) and yields a total ocean bottom to mantle thickness of 4–7 km. 相似文献
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The state of the art in underwater acoustic telemetry 总被引：6，自引：0，他引：6
Progress in underwater acoustic telemetry since 1982 is reviewed within a framework of six current research areas: (1) underwater channel physics, channel simulations, and measurements; (2) receiver structures; (3) diversity exploitation; (4) error control coding; (5) networked systems; and (6) alternative modulation strategies. Advances in each of these areas as well as perspectives on the future challenges facing them are presented. A primary thesis of this paper is that increased integration of high-fidelity channel models into ongoing underwater telemetry research is needed if the performance envelope (defined in terms of range, rate, and channel complexity) of underwater modems is to expand 相似文献
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A modulation technique for increasing the reliable data rate achievable by an underwater acoustic communication system is presented and demonstrated. The technique, termed spatial modulation, seeks to control the spatial distribution of signal energy such that the single physical ocean channel supports multiple parallel communication channels. Given a signal energy constraint, a communication architecture with access to parallel channels will have increased capacity and reliability as compared to one with access to a single channel. Results from two experiments demonstrate higher obtainable data rates and power throughput for a system employing spatial modulation than for one that does not. The demonstrated benefits were characterized by an equivalent SNR gain of over 5 dB in the first experiment. In the second experiment, using two element source and receiver arrays with apertures of 0.9 m, a coherently modulated signal was shown to offer nearly 50% greater capacity by using spatial modulation than by using temporal modulation alone. 相似文献
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Acoustic telemetry--An overview 总被引：1，自引：0，他引：1
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 underwater telephones, FM 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. 相似文献
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Scattering functions from several experiments demonstrate that acoustic underwater channels are doubly spread. Receivers used on these channels to date have difficulty with large Doppler spreads. A receiver to perform coherent communication over Doppler spread channels is presented in this first paper of two. The receiver contains a channel tracker and a linear decoder. The tracker operates by means of a modified recursive least squares algorithm which makes use of frequency-domain filters called Doppler lines. The decoder makes use of the channel tracker coefficients in order to perform minimum mean square error decoding. This first paper treats theoretical aspects whereas the second part presents implementation issues and results 相似文献
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For pt. I see ibid., vol. 25, no. 1, p. 62-72 (2000). A receiver for coherent communication through underwater communication channels is analyzed. The receiver performance and stability versus delay spread, Doppler spread, and signal-to-noise ratio is quantified. The stability is governed by the ill-conditioning of a correlation matrix estimate and it sets the limit on how many taps should be used for a channel with a given number of degrees of freedom. The receiver is used extensively on both simulated and real data that are Doppler spread, and good performance in these channels is verified 相似文献
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Dushaw B.D. Howe B.M. Mercer J.A. Spindel R.C. Baggeroer A.B. Menemenlis D. Wunsch C. Birdsall T.G. Metzger K. Clark C. Colosi J.A. Comuelle B.D. Dzieciuch M. Munk W. Worcester P.F. Costa D. Forbes A.M.G. 《Oceanic Engineering, IEEE Journal of》1999,24(2):202-214
Acoustic signals transmitted from the ATOC source on Pioneer Seamount off the coast of California have been received at various sites around the Pacific Basin since January 1996. We describe data obtained using bottom-mounted receivers, including US Navy Sound Surveillance System arrays, at ranges up to 5 Mm from the Pioneer Seamount source. Stable identifiable ray arrivals are observed in several cases, but some receiving arrays are not well suited to detecting the direct ray arrivals. At 5-Mm range, travel-time variations at tidal frequencies (about 50 ms peak to peak) agree well with predicted values, providing verification of the acoustic measurements as well as the tidal model. On the longest and northernmost acoustic paths, the time series of resolved ray travel times show an annual cycle peak-to-peak variation of about 1 s and other fluctuations caused by natural oceanic variability. An annual cycle is not evident in travel times from shorter acoustic paths in the eastern Pacific, though only one realization of the annual cycle is available. The low-pass-filtered travel times are estimated to an accuracy of about 10 ms. This travel-time uncertainty corresponds to errors in range- and depth-averaged temperature of only a few millidegrees, while the annual peak-to-peak variation in temperature averaged horizontally over the acoustic path and vertically over the upper 1 km of ocean is up to 0.5°C 相似文献