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The high-frequency acoustic properties of seafloor sediments are very significant in seafloor study and underwater acoustic study field. In order to measure the sound speed and the attenuation for the small-scale sediment cores more accurately, this study developed a water coupled acoustic laboratory measurement system based on Richardson-Briggs technique. This method used the correlation comparison of waveforms received in sediment core and in identical reference tubes filled with water to measure sound speed and attenuation. The sound speed and attenuation of a clayey silt sediment sample were measured using the water coupled acoustic laboratory measurement system. This frequency dependence of the sound speed and attenuation showed that the clayey silt sediment has a weak positive sound speed dispersion, while the attenuation increases with a strong positive gradient within the measurement frequency range. This study also noted that the measured sound speed ratio match well with the empirical equations from literature. The measured attenuation factor data can fall in the Hamilton's empirical prediction range. [ABSTRACT FROM AUTHOR]

To accurately characterize sound speed dispersion of shallow sediments in the Southern Yellow Sea, three types of sediments, i.e., silt, clayey silt, and silty clay, were selected to measure the sound speeds at 25-250 kHz. Over the frequency range, the sound speeds vary approximately from 1,536 to 1,565 m s−1 in silt sediment, from 1,511 to 1,527 m s−1 in clayey silt sediment, and from 1,456 to 1,466 m s−1 in silty clay sediment. The sound speed exhibits a slow increase with frequency in a nearly linear gradient, but these three types of sediments have different sound speed dispersion characteristics. The silt sediment with relatively coarse grains has the most significant sound speed dispersion, while the sound speed dispersions of the two others are relatively weak. Comparison between the measured dispersions and the model predictions shows that the grain-shearing model can match the measured data at most of frequencies. Nevertheless, when the grain bulk modulus was assigned 3.2 × 1010 Pa according to relevant references, the Biot-Stoll model predictions were higher than the measured values at high frequencies; when it was assigned a relatively small value of 2.8 × 1010 Pa, the model predictions achieved optimal matching with the measured values. [ABSTRACT FROM AUTHOR]

Based on a substantial number of seabed sediment samples and corresponding acoustic characteristic and physical property test data collected in the continental shelf area of the northwestern South China Sea, this study employed a sound speed ratio correction model to analyze the correlation between the sound speed ratio of seabed sediments and parameters such as porosity, density, mean grain size, and water content. This study resulted in the development of both single-parameter and double-parameter empirical formulas for the sound speed ratio of seabed sediments in this marine region. The determination coefficients (r2) for the single-parameter empirical formulas based on physical properties, excluding the mean grain size (r2 ≤ 0.75), were all above 0.78, indicating a strong correlation. Additionally, the fitting curve at 100 kHz was slightly greater than that at 50 kHz, consistent with the acoustic dispersion characteristics of sediments. To assess the applicability of the empirical formulas to different maritime areas, the formulas derived from the South Yellow Sea, East China Sea, and South China Sea were compared with those of the study area. The results indicated that the empirical formulas for the sound speed ratio established in this study have general applicability, especially for sediments with low porosity, high density, and low mean grain size. In addition, the determination coefficient of the dual-parameter empirical formula for the sound speed ratio–porosity–mean grain size is superior to that of the single-parameter empirical formula for the sound speed ratio–mean grain size. Through comparative studies with other marine areas, it was found that there are certain differences in the relationships between porosity and mean grain size established in different marine areas. Therefore, based on the rough sphere model, this study transforms the GS model into a single-parameter model built on either porosity or mean grain size. The error analysis results indicate that the single-parameter GS model has a smaller error than the measured data. However, the GS model controlled by a single parameter performs poorly compared to the predicted curves of the sound speed ratio–porosity and the sound speed ratio–mean grain size fitted in this study. This discrepancy may be attributed to the fact that the input parameters of the GS model are reference values, emphasizing the need for further research to determine suitable input parameters for the GS model in this marine area. • The empirical equations for the sound speed ratio were developed in this study in different marine regions. • The established empirical equations for the study area were compared with those for the South Yellow Sea, East China Sea, and other marine regions. • This study compared the empirical equations with the grain shearing (GS) theoretical model. [ABSTRACT FROM AUTHOR]

The frequency dependence of the sound speed and attenuation in seafloor sediments was measured in a laboratory by using a probe method at the frequency range of 25–250 kHz. The standard deviation of repeated sound speed measurement in fresh water is about 2.82 m/s. Repeated measurement of attenuation shows a minimum standard deviation of 0.58 dB at 25 kHz and a maximum standard deviation of 3.06 dB/m at 250 kHz. The measurement results indicate that the sound speeds vary from 1638 to 1658 m/s in sandy silt sediments and from 1548 to 1571 m/s in clayey silt sediments. The attenuation increases from 14.2 to 51.9 dB/m in sandy silt sediments and from 7.8 to 31.7 dB/m in clayey silt sediments. The measured sound speed dispersion in sandy silt sediment agrees reasonably with the predictions of the Biot-Stoll model, the Grain-Shearing model, and the Effective Density Fluid model (EDFM). The measured sound speed in clayey silt sediment agrees better with the predictions of the GS model than that of the Biot-Stoll model and the EDFM. The measured attenuation is more consistent with f 1/2 dependence than the f 1 dependence, and is similar to the predictions of Biot-Stoll model and the EDFM. [ABSTRACT FROM AUTHOR]

Highlights: [•] The in situ acoustic properties are acquired using a completely new apparatus. [•] Relations between acoustic properties and the geotechnical parameters are obtained. [•] Reasons contribute to the relations are analyzed. [•] Velocity shows good correlation with geotechnical parameters. [•] Attenuation shows weak correlation with geotechnical parameters. [Copyright &y& Elsevier]