Characteristics of Very Low Frequency Sound Propagation in Full Waveguides of Shallow Water

Li, Nansong; Zhu, Hanhao; Wang, Xiaohan; Xiao, Rui; Xue, Yangyang; Zheng, Guangxue

doi:10.3390/s21010192

Cited by 6 publications

(3 citation statements)

References 27 publications

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“…Due to the development of submarine stealth technology and the requirements for monitoring various physical ocean phenomena, the detection methods for targets in shallow water gradually turn to very low frequency (VLF, ≤100 Hz) [9]. VLF acoustic signals with strong penetrating power penetrate the sea bottom when propagating in the shallow sea.…”

Section: Introductionmentioning

confidence: 99%

[Retracted] Analysis of VLF Wave Field Components and Characteristics Based on Finite Element Time‐Domain Method

et al. 2023

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Most traditional sound field calculation methods regard the seabed as the horizontal stratified liquid sea bottom and conduct simulation analysis based on the frequency domain. Hence, the generality of the above research methods is limited to varying degrees. To accurately clarify the propagation characteristics and mechanism of very low-frequency (VLF, ≤100 Hz) sound waves in the shallow sea, a numerical calculation model is established using the finite element time-domain method (FETD) based on the three-dimensional cylindrical coordinate system. Using this model, the effects of sea-bottom topographies and geoacoustic parameters on the composition and characteristics of VLF sound fields in the shallow sea and their corresponding mechanism are investigated through the comparative analysis of various numerical simulation examples. The simulation results demonstrate that the low-frequency sound field in the full waveguide of the shallow sea is composed of normal mode waves in the seawater layer, Scholte waves at the liquid-solid interface, and elastic waves at the sea bottom. Compared with the soft sea bottom, which has a more negligible elastic impedance, the hard sea bottom is more conducive to the long-distance propagation of normal mode waves and the excitation of Scholte waves. The Scholte waves on the hard sea bottom are significantly stronger than those on the soft sea bottom. Compared with the horizontal sea bottom, the uphill topography enhances the sound energy leakage to the sea bottom. It is more favorable to receive Scholte waves at shallow depths, whereas the influence laws of downhill topography are the opposite.

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Section: Introductionmentioning

confidence: 99%

[Retracted] Analysis of VLF Wave Field Components and Characteristics Based on Finite Element Time‐Domain Method

et al. 2023

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“…Hence, higher energy density will be required for a longer distance (>100 m) underwater [16,17]. This reason supports the KHz range frequencies for underwater wireless power transfer [18]. However, high frequencies can further be investigated for near field applications (<10 m) in order to estimate the guided wave and their applications [19,20].…”

Section: Acoustic Pressure Fieldmentioning

confidence: 84%

Impact of THz Frequency on Underwater Acoustic Wave Propagation for Short Range Wireless Applications

Awal

Yahya

Afrizal

et al. 2021

CFDL

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Acoustic propagation in seawater is an important aspect of scientific investigation. However, the impact of the THz scale frequencies for acoustic propagation is not included in the studies. Thus, a finite element analysis of such propagation in a seawater medium is presented in this paper applying THz frequencies. A transmitter (circular with a diameter of 14 mm, a thickness of 3 mm) and a rectangular receiver (20×10×0.5 mm3) are designed to trace the variations in the propagation mediums. A propagation medium of seawater (70×40×60 mm3) with ice and softwood is modelled. A scale of frequencies (1 kHz to 1 THz) is applied to trace the impact on the propagation pattern. It is found that THz range frequencies provide a very small wavelength. As a result, the potential propagation distance is very small. As such, the sound pressure level, displacements of the receiver and pressure field shows very rapid drops in the magnitude. This work considers only 70 mm as propagation distance, yet the sharp decrement of performance parameters suggests that it is rather inconvenient to achieve useful efficiency using THz frequencies for acoustic propagation.

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“…Firstly, low-frequency emissions, such as those earmarked by the Decision, are easily absorbed in the shallow waters of some European seas, including the western Mediterranean Sea and the Baltic Sea. This consequently raises challenges in appropriately characterising and mapping out shipping noise in European waters [12]. Secondly, many researchers claim that the high presence of recreational vessels, such as sailboats, in European coastal waters is a dominant threat to the integrity of the marine soundscape as these vessels emit sound at higher frequencies than commercial ships.…”

Section: Introductionmentioning

confidence: 99%

A Preliminary Snapshot Investigation of the Marine Soundscape for Malta: A Steppingstone towards Achieving ‘Good Ecological Status’

Filletti,

Gauci,

Deidun

et al. 2023

JMSE

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The ever-accelerating rate of research focusing on the issue of underwater noise pollution, particularly concerning low-frequency, continuous noise, has steadily been unveiling the myriad of detrimental ecological implications caused to marine life. Despite this, many European Member States, such as Malta, still lack solid monitoring and regulatory frameworks aimed at characterising and improving the state of the marine acoustic environment and achieving ‘Good Ecological Status’ in accordance with the Marine Strategy Framework Directive. This shortcoming is directly reflected in the complete absence of baseline information covering the quality of the national soundscape. This paper aims to serve as a preliminary investigation into continuous underwater noise generation within Maltese waters, focusing on two sites characterised by heavy marine activity: Ċirkewwa and the Grand Harbour. Digital signal processing software packages (dBWav version 1.3.4) were used to extract and analyse sound pressure levels from in situ recorded audio files. Further statistical analysis was also carried out so as to evaluate the resultant snapshot of the baseline marine soundscapes at both sites. Furthermore, AIS data were used to tentatively identify the identifiable sources of underwater noise pollution. Given the current information lacuna revolving around the issue of underwater noise pollution in Malta, this paper may serve as a pilot study, with the aim of bridging this knowledge gap and forming the basis of future national research for Maltese marine conservation.

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Characteristics of Very Low Frequency Sound Propagation in Full Waveguides of Shallow Water

Cited by 6 publications

References 27 publications

[Retracted] Analysis of VLF Wave Field Components and Characteristics Based on Finite Element Time‐Domain Method

[Retracted] Analysis of VLF Wave Field Components and Characteristics Based on Finite Element Time‐Domain Method

Impact of THz Frequency on Underwater Acoustic Wave Propagation for Short Range Wireless Applications

A Preliminary Snapshot Investigation of the Marine Soundscape for Malta: A Steppingstone towards Achieving ‘Good Ecological Status’

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