Investigation of long-range sound propagation in surface ducts

Duan, Rui; Yang, Kunde; Ma, Yuanliang

doi:10.1088/1674-1056/22/12/124301

Cited by 11 publications

(3 citation statements)

References 17 publications

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“…The acoustic propagation experiments in low-salinity water, conducted on the west coast of Canada [4] and the Baltic Sea [5], verified that the SSD behaved like an acoustic waveguide with optimum duct propagation. Those experimental results can be well explained by theoretical studies [6][7][8][9][10]. However, this work focused on sound transmission and did not provide an indepth analysis of the causal link between the freshening process and the SSD.…”

Section: Introductionmentioning

confidence: 89%

Analysis of Surface Sound Duct in the Northern Shelf of the South China Sea

Piao

Zhou

et al. 2018

Shock and Vibration

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The northern shelf of the South China Sea (NSSCS) is characterized by surface low-salinity water due to discharge from the Pearl River. In such an environment, the surface sound duct (SSD) is the most important duct for near-surface sonar applications. Nevertheless, the mechanism of SSD formation is very complicated and is influenced by salinity, temperature at the air-sea interface, and various additional marine phenomena. In this study, an 8-year conductivity-temperature-depth (CTD) profile of the NSSCS was used to analyze the SSD formation. An advanced diagrammatic method is proposed to provide a quantitative analysis of the contribution of salinity, temperature, and hydrostatic pressure on SSD formation. Large salinity gradient (0.25 psu/m) was shown to play a crucial role in SSD formation when a mixed layer exists. As representative examples, the sea under cold surges, typhoon genesis, and low-salinity lenses were studied. Conversely, the absence of SSDs in low-salinity water was also observed in upwelling regions. This study further showed that highly negative temperature gradients affect SSD formation even in low-salinity water. Furthermore, although the duct depth of a low-salinity SSD is usually less than 10 meters, it still can serve as an effective duct for acoustic propagation.

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Section: Introductionmentioning

confidence: 89%

Analysis of Surface Sound Duct in the Northern Shelf of the South China Sea

Piao

Zhou

et al. 2018

Shock and Vibration

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“…The features of the duct, including oceanographic and acoustic characteristics, have been studied extensively. [1][2][3] At high frequency, the sound is trapped in the duct and analysis of energy loss due to ocean water absorption 4,5 or ocean surface scattering 6,7 has been reported. In contrast, at low frequency the sound energy leaks out of the duct due to diffraction.…”

Section: Introductionmentioning

confidence: 99%

A simple expression for sound attenuation due to surface duct energy leakage in low-latitude oceans

Duan

Yang

et al. 2016

The Journal of the Acoustical Society of America

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This paper presents an expression for the attenuation of sound energy in an ocean surface duct due to energy leakage outside the duct. Dominant parameters determining the attenuation are the sound frequency and the surface duct thickness. The attenuation is found to be exponentially dependent on a scaled frequency that combines the two parameters. Data from experiments in low-latitude oceans with three different surface duct thicknesses are used to verify the exponential expression derived for the attenuation.

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“…Avilov [3] points out that there is an optimal frequency of the shadow zone insonification, which corresponds to the critical frequency of the surface duct. Given that the formula [6] to calculate the critical frequency is 𝑓 c = 183700𝑧 −2/3 d , there will be an optimal MLD for each source frequency. Here 𝑓 c is the critical frequency, which is the frequency corresponding to the direct ray grazing the bottom of the surface duct, and 𝑧 d refers to the MLD.…”

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confidence: 99%

Comparison of Surface Duct Energy Leakage with Bottom-Bounce Energy of Close Range Propagation

Cheng

Yang

et al. 2016

Chinese Phys. Lett.

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For close range (almost 8–15 km) propagation, bottom-bounce energy (BBE) usually suffers from a great transmission loss due to a large grazing angle interacting with the ocean bottom, and the surface duct energy leakage (SDEL) might be able to make a significant contribution to shadow zone insonification. This study aims at making a comparison between SDEL and BBE in a shadow zone with a source depth of 50 m for close range propagation. Analysis of experimental data shows that for lower frequencies the SDEL can be comparable with the BBE up to a range of 12 km. Numerical simulations suggest that the transmission loss (TL) of 90 dB is a proper value to quantify the role of the SDEL in shadow zone insonification. When TL of the SDEL is about 90 dB, it is believed to be comparable with the BBE. Studies on the effect of mix layer depth (MLD) on the SDEL indicate that larger MLD and lower frequencies can help to create favorable conditions for SDEL and that there exists an optimal MLD for SDEL at certain frequency. Statistics of MLD distribution in the South China Sea (SCS) show that winter is favorable for SDEL and the situation reverses in summer. Eddies are known to occur frequently in the SCS and the study on the effect of eddies on the SDEL suggests that the presence of an eddy will influence the SDEL significantly by modifying the MLD.

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Investigation of long-range sound propagation in surface ducts

Cited by 11 publications

References 17 publications

Analysis of Surface Sound Duct in the Northern Shelf of the South China Sea

Analysis of Surface Sound Duct in the Northern Shelf of the South China Sea

A simple expression for sound attenuation due to surface duct energy leakage in low-latitude oceans

Comparison of Surface Duct Energy Leakage with Bottom-Bounce Energy of Close Range Propagation

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