Sound Velocity and Attenuation Forecasting of Seafloor Sediments

The seafloor is an important boundary for the ocean acoustic field, and understanding the properties of seafloor sediment is a necessary prerequisite for studying the ocean acoustic field. Currently, liquid seafloor is commonly used in the inversion of seafloor low-frequency acoustic parameters. However, the actual seafloor is a porous elastic medium composed of a solid framework and pore water. Therefore, this article predicts the sound velocity and attenuation coefficient of seafloor sediments using the approximate fluid density theory derived from Biot's theory. The results show that the sound velocity of seafloor sediments is similar to that of seawater in the frequency range of 10 Hz to 100 kHz. The relationship between the attenuation coefficient of seafloor sediments and frequency exhibits a characteristic frequency. When the frequency is lower than the characteristic frequency, the attenuation coefficient is proportional to the square of the frequency. When the frequency is higher than the characteristic frequency, the attenuation coefficient is proportional to the square root of the frequency. In addition, the article presents the relationship between the real and imaginary parts of the approximate density and frequency, as well as the comparison with the true density. In the low-frequency band, the approximate density real part coincides with the true density due to the same movement direction of the sediment framework and pore water. In the high-frequency band, the approximate density is lower than the true density due to the relative motion between the sediment framework and pore water. This lays the foundation for the calculation of seafloor propagation loss and the inversion of seafloor low-frequency acoustic parameters in the future.