High frequency dependence of sound speed and attenuation in coral sand sediments

Abstract The acoustic properties of seafloor coral sand sediments are of significant meaning for accurately modeling underwater sound propagation in sea areas around coral reef islands. To ultrasonically measure coral sand sediments with different grain sizes, sediment samples from coral islands were screened and remolded into five types of samples with different grain sizes. This study measured the sound speed and attenuation in the frequency range of 27–247 kHz and analyzed the frequency dependence of the acoustic properties. The results showed that the sound speed increased significantly with frequency, suggesting an approximately linear relation. The sound speed dispersion in the coarse-grained sediments was larger than that in the fine-grained sediments. The measured attenuation data showed a variable frequency dependence among the different sediment types. The measured data were compared with Biot-Stoll model (BS model) predictions, and the fitting results showed that intergranular pores can lead to sound speed data-model mismatches. The attenuation data-model comparisons revealed that sediments with different grain sizes have different sound wave energy loss mechanisms. The BS model with grain contact squirt flow and shear drag (BICSQS model) can match the attenuation data more consistently than the BS model. The results show that scattering is an important factor in sound attenuation in coral sand sediment and the attenuation scattering factors for different grain size sediments were provided.