Environmental factors affecting acoustic velocity of seafloor surface sediments

With the comprehensive analysis of measurement results by the temperature pressure controlled experiment and theoretical calculations with the general model of sound speed,the influence mechanism and characteristics of environmental factors affecting acoustic velocity of seafloor surface sediments are studied for the three main acoustic measurement methods including the geoacoustic inversion,the underwater in situ acoustic measurement and the sampling sample acoustic measurement.The consistency between theoretical calculation and experimental measurement reveals the main mechanism of the influence of temperature and hydrostatic pressure on the velocity of compressional wave of the surface sediments,which is achieved by their effect on the density,viscosity and bulk modulus of the pore water.At the same time,it is found that the sound velocity ratio isn't constant and slightly decreases both with the increase of temperature and with that of hydrostatic pressure.In the normal range of temperature and hydrostatic pressure for the seafloor sediment at the depth of form 0 m to 4000 m,the fluctuation of acoustic velocity ratio of seafloor surface sediment and bottom sea water is within 2% by theoretical calculation and within 2.73% by experimental measurement.Based on the sound velocity ratio being not constant,a modified sound velocity ratio correction model is proposed,which provides a improved method to reduce the influencing error of temperature and hydrostatic pressure to more accurately realize the comparison and analysis of the sound velocity of the seafloor sediments under the different in situ and laboratory conditions.