A predictive model for acoustic dispersion and attenuation in gassy sediments is proposed. The model combines the linear solution for gas-bubble pulsations in a viscoelastic medium with corrected Biot equations involving gas-bubble pulsations. Numerical results for sound speed and attenuation are compared with predictions from Anderson and Hampton's model to demonstrate the advantages of the proposed model. The most important advantage of the current model is that it combines the dispersion regimes associated with gas-bubble pulsations and relative motion between the pore water and solid framework. The reflection coefficient at the water/gassy-sediment interface is derived based on the current model, and numerical results show that gas-bubble resonance can lead to the highest reflection. This model can also be used with a full acoustic inversion to estimate gas-bubble size distributions.

This study investigates acoustic propagation and transmission loss in shallow water at an unexplored site in the northern Arabian Sea near the Pakistan coastline using a normal mode theoretical framework. Sound propagation in shallow water with range-independent bathymetry was analyzed using a customized Kraken C program to compute eigenvalues and eigenfunctions. The sound speed profile and clay silt sediment samples of the northern Arabian Sea, which characterize the water column and ocean bottom, respectively, were determined. Coherent and incoherent transmission losses for frequencies ranging from 50 to 500 Hz were calculated across different ranges and depths. Results indicate significant intensity fluctuations with increasing range, leading to higher transmission loss. Low frequencies (50–225 Hz) exhibit more significant transmission loss, while higher frequencies (230–500 Hz) show reduced loss. Transmission loss is higher for receivers at 19 m depth compared to those at shallower depths (8 m and 12 m) because the receivers are positioned near the layer of bottom sediments. Factors such as source and receiver depth, sediment properties, bottom roughness, and sound frequency significantly influence transmission loss. The novel dataset for the region supports the assessment of sonar performance, underwater communication, navigation, and marine life exploration.

A corrected effective density fluid model is developed for predicting sound speed dispersion and attenuation coefficient in gassy sediments. An acoustic experiment was undertaken to measure the attenuation coefficient in a frequency band of 600 to 3000 Hz in gassy unsaturated sand. The measured frequency spectra of the attenuation coefficient show four peaks due to bubble resonance. Then a method of using several modified Gaussian functions to model bubble size distribution is proposed to fit measured attenuation data, which shows that the magnitudes of the fitted model attenuation coefficients are broadly in agreement with those measured attenuation data.

基阵的信噪比增益与噪声场空间特性密切联系, 海洋环境噪声空间特性建模始终是水声学研究的热门问题. 声纳功能不同, 其工作频段和带宽通常也不相同, 因此, 任意频带噪声场的空间相关系数对声纳系统设计具有重要参考价值. 依据海洋环境噪声场的产生过程, 在高频近似条件下, 本文提出一种噪声场时域建模方法, 给出了水平分层介质中表面噪声时域声压和质点振速的积分表示, 为噪声矢量场宽带模型的建立奠定了基础. 根据风成噪声谱结构, 数值计算了不同频带、不同谱斜率的噪声场空间相关系数, 揭示了带宽、谱结构对风成噪声空间特性的影响规律. 随着阵元间距和带宽增大, 噪声矢量场各分量的空间相关系数的振荡周期数逐渐减少, 振荡幅度逐渐减小, 这是由于噪声场相关系数频域平均的结果. 当谱斜率小于零时, 宽频带噪声场的空间相关半径大于窄带噪声场的相关半径, 这是由于低频段噪声起主要贡献的结果, 实测海洋环境噪声声压场竖直方向空间相关特性变化规律与理论结果一致. 本文模型对换能器成阵技术研究以及环境参数反演具有潜在应用前景.

The spatial correlation function for broadband ocean surface noise is considered in horizontally stratified media. It is expressed as an integral over the correlation function of the sound field radiated by a single noise source in the waveguide, assuming spatially uncorrelated noise sources with the same intensity that are distributed on the sea surface uniformly. An equation for the spatial-temporal correlation coefficient of the surface noise in a certain frequency band can then be derived. Numerical simulations are carried out for band limited white noise and wind noise, which show that the fluctuation of the correlation coefficient decreases with increasing bandwidth.