Influence of Temperature on Acoustic Sound Speed and Attenuation of Seafloor Sand Sediment

The temperature dependence of the parameters within an effective density fluid model that incorporates the effects of granularity is used to examine sound speed and attenuation of sand within the temperature range of 1 ^°C-30 ^°C. Analysis of the behavior of attenuation as a function of frequency and permeability over the above temperature range give some new insights. In particular, the attenuation coefficient can either increase or decrease with temperature depending on the physical parameters and the frequency range being examined. A relaxation frequency is defined that separates frequency ranges where attenuation temperature dependence changes. Below the relaxation frequency, attenuation increases with temperature, and above this frequency, attenuation decreases with temperature. The analysis of the effect of sand sediment physical parameters on acoustic properties versus temperature also reveals the unique role of permeability. An “attenuation transition permeability” is also defined. As temperature increases, attenuation increases if the static permeability is less than the attenuation transition permeability and decreases if the static permeability is greater than the attenuation transition permeability. The comparison of experimental data sets with calculations using the temperature-dependent effective density fluid model indicates the dominant role of pore water both on the temperature-dependent sound speed and attenuation of sand sediment and gives support to use of an effective-density-based model.