The effective depth of a Pekeris ocean waveguide, including shear wave effects

The debate on the sound speed dispersion and the frequency dependence of sound attenuation in seabottoms has persisted for decades, mainly due to the lack of sufficient experimental data in the low-frequency (LF) to high-frequency speed/attenuation transition band. This paper analyzes and summarizes a set of LF measurements in shallow water that have resulted in the identification of nonlinear frequency dependence of sound attenuation in the effective media of sandy seabottoms. The long-range acoustic measurements were conducted at 20 locations in different coastal zones around the world. The seabed attenuations, inverted from different acoustic field measurements and characteristics, exhibit similar magnitude and nonlinear frequency dependence below 1000 Hz. The resulting effective sound attenuation can be expressed by alpha(dB/m)=(0.37+/-0.01)(f/1000)((1.80+/-0.02)) for 50-1000 Hz. The corresponding average sound speed ratio at the bottom-water interface in the 50-600 Hz range is 1.061+/-0.009. Both the LF-field-derived sound speed and attenuation can be well described by the Biot-Stoll model with parameters that are consistent with either theoretical considerations or experimental measurements. A combination of the LF-field-inverted data with the SAX99, SAX04, and other high-frequency measurements offers a reference broadband data set in the 50-400 000 Hz range for sonar prediction and sediment acoustics modeling.

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“…͑1͒, and the shear wave in the sediment is neglected, then one can obtain [26][27][28][29]75 Q͑f͒ = 0.0366…”

Section: A Frequency Dependence Of Bottom Reflection Loss At Small Gmentioning

confidence: 99%

Low-frequency geoacoustic model for the effective properties of sandy seabottoms

Zhou

Zhang

Knobles

2009

The Journal of the Acoustical Society of America

113

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“…The term "effective depth" to describe this approximation was introduced by Buckingham. 21 Later, the effective depth technique has been used by Chapman et al 22 to describe approximately the reflection characteristics of various types of representative shear wave supporting bottom. The effective depth approximation was extended by Zhang and Tindle.…”

Section: Normal Modes Approachmentioning

confidence: 99%

“…Combining Eqs. (22) and (23) A new method for finding this curve more efficiently has been recently proposed. 25 …”

Section: Normal Modes Approachmentioning

confidence: 99%

The peculiarities of the implementation of time reversal method for gas leakage detection on Sakhalin shelf

Polovinka¹,

Maksimov²

2015

Proceedings of Meetings on Acoustics

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In this report, temporal and spatial focusing properties of time-reversal mirrors are studied for leakage detection under specific conditions of the northeast shelf of Sakhalin Island. Two factors, the local character of the acoustic emission signal caused by the leakage and a resonant nature of the bubble radiation at its birth, make particularly effective scattering with the conjugate wave (CW). In the vicinity of the drilling platforms located on the shelf of Sakhalin, the long-term studies of features affecting propagation of acoustic signals were performed and a consistent model to simulate acoustic environment was derived. We obtained an integral representation for the required quantity -time reversed field near the source in terms of Green's function of the Pekeris waveguide. The specific of the problem is the shape of the acoustic signal which allows one to calculate analytically the integral over the frequencies. The range of leak detection is not very large (hundreds of meters), and the array can get a limited number of signals propagating along different paths in the waveguide which can be used for a sufficiently reliable detection of the events.

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“…D'Spain et al [29] developed an adiabatic normal-mode model to analyze broadband, matched-"eld-processing data collected in shallow water. The model incorporated the concept of &&e!ective depth'', which was "rst introduced by Weston [30] for a Pekeris waveguide and later extended by Chapman et al [31] to include shear waves. In essence, the phase change associated with the re#ection of a plane wave from a #uid}elastic interface at the bottom is equal to that from a pressure-release boundary that is o!set a distance below the true bottom.…”

Section: 222mentioning

confidence: 99%

Recent Advances in Underwater Acoustic Modelling and Simulation

Etter

2001

Journal of Sound and Vibration

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The effective depth of a Pekeris ocean waveguide, including shear wave effects

Cited by 28 publications

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Low-frequency geoacoustic model for the effective properties of sandy seabottoms

Low-frequency geoacoustic model for the effective properties of sandy seabottoms

The peculiarities of the implementation of time reversal method for gas leakage detection on Sakhalin shelf

Recent Advances in Underwater Acoustic Modelling and Simulation

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