A long-range and variable focus phase-conjugation experiment in shallow water

Hodgkiss, William S.; Song, H. C.; Kuperman, W. A.; Akal, T.; Ferla, C.; Jackson, D.R.

doi:10.1121/1.426740

Cited by 180 publications

(89 citation statements)

References 13 publications

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“…The striation pattern is steeper, and while the concept of an invariant remains plausible a larger numerical value is in order. The result is consistent with a recent field experiment where both source and receivers were below the thermocline and ß =1.4 was observed [8].…”

Section: Range-independent Scenariossupporting

confidence: 82%

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Effect of shallow water internal waves on ocean acoustic striation patterns

Rouseff

2001

Waves in Random Media

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Contour plots of underwater acoustic intensity, mapped in range and frequency, often exhibit striations. It has been claimed that a scalar parameter "beta," defined in terms of the slope of the striations, is invariant to the details of the acoustic waveguide. In shallow water, the canonical value for beta is one. In the present paper, the waveguide invariant is modeled as a distribution rather than a scalar. The effects of shallow water internal waves on the distribution are studied by numerical simulation. Realizations of time-evolving shallow water internal wave fields are synthesized and acoustic propagation simulated using the parabolic equation method. The waveguide invariant distribution is tracked as the internal wave field evolves in time. Both random background internal waves and more event-like solitary internal waves are considered. Abstract. Contour plots of underwater acoustic intensity, mapped in range and frequency, often exhibit striations. It has been claimed that a scalar parameter "beta," defined in terms of the slope of the striations, is invariant to the details of the acoustic waveguide. In shallow water, the canonical value is ß = 1. In the present paper, the waveguide invariant is modeled as a distribution rather than a scalar. The effects of shallow water internal waves on the distribution are studied by numerical simulation. Realizations of time-evolving shallow water internal wave fields are synthesized and acoustic propagation simulated using the parabolic equation method. The waveguide invariant distribution is tracked as the internal wave field evolves in time. Both random background internal waves and more event-like solitary internal waves are considered.Note: A version of this report was submitted to the journal Waves in Random Media. 097Ocean acoustic striation patterns

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Section: Range-independent Scenariossupporting

confidence: 82%

“…More recently, the concept has received attention in the Western literature [7]. It was used to move the focal range in a phase conjugation experiment [8]. The theory was extended to environments varying in azimuth and used in the analysis of single receiver spectrograms [9].…”

Section: Introductionmentioning

confidence: 99%

Effect of shallow water internal waves on ocean acoustic striation patterns

Rouseff

2001

Waves in Random Media

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“…In recent times, extensive research has been conducted on time reversal waves (phase conjugate waves) in ocean acoustics [1][2][3][4][5][6][7][8][9][10]. In ocean acoustics, time reversal waves are used as follows: Acoustic waves transmitted from a source are received at the time reversal mirror (TRM) array; these signals are reversed in the time domain (which corresponds to phase conjugate signals in the frequency domain); these time-reversed signals are retransmitted from the TRM array; and they converge to the focus where the original source existed, even in unknown and inhomogeneous media.…”

Section: Introductionmentioning

confidence: 99%

A study on the focusing property of time reversal waves in shallow water

Shimura

2004

Acoust. Sci. & Tech.

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The focusing property of time reversal waves (phase conjugate waves) in shallow water or the deep sea has been discussed based on simulations of the normal mode method. In this study, the focusing property of time reversal waves was verified through tank experiments and it was concluded that time reversal waves enable acoustic waves to be converged to the focus. Further, the simulation results qualitatively concurred with the experimental results. This study also investigated how the configuration of the elements of the Time Reversal Mirror (TRM) array affects the focusing property, and the following matters were clarified: The signal received at the focus is not disrupted when the number of elements in the TRM array is reduced. Even if the TRM array is tilted or the heights of its elements are steadily shifted, the signal received at the focus is not disrupted. However, if the tilting or the height-shifting is not stationary, the time reversal waves lose their focusing property. Even a horizontal TRM array can generate time reversal waves if it is of adequate length.

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“…This is an important issue since in practical applications the medium properties may change during the experiment [12,15]. Some experimental studies have also shown that the refocused signal is modified as the underlying medium changes [25,34]. Therefore, we analyze time reversal experiments in a slightly different setting than the one described above.…”

Section: Introductionmentioning

confidence: 99%

Time reversal of waves in a weakly perturbed random medium

Vigo¹,

Sølna²

2008

Communications in Mathematical Sciences

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Abstract. In a time reversal experiment, a signal recorded by an array of transducers and sent back time-reversed into the same medium approximately refocuses on the original source center. The refocusing resolution is improved in an inhomogeneous medium. In this work we study the effect of changes in the medium, namely, the case when back propagation takes place in a perturbed medium.Under the paraxial approximation assumption for a medium with weak inhomogeneities we consider a high frequency white noise regime. We show that relatively small perturbations do not affect the stable refocusing (self-averaging) for a localized source, but produce an interesting blurring of the refocused time signal. In some simple situations this effect can be explicitly quantified and related to the statistical model for the medium.

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A long-range and variable focus phase-conjugation experiment in shallow water

Cited by 180 publications

References 13 publications

Effect of shallow water internal waves on ocean acoustic striation patterns

Effect of shallow water internal waves on ocean acoustic striation patterns

A study on the focusing property of time reversal waves in shallow water

Time reversal of waves in a weakly perturbed random medium

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