Abstract: In order to study of sound attenuation characteristics of seabed sediment at small scale, an original method for measuring acoustic attenuation of sediment within a small-gap cross section is put forward. There are small disturbances in the sediment samples during the course of measurement by the method. The sound attenuation of seafloor sediment can be measured at two test points; the distance of them is less than one wavelength, which provides a method for finding out how microstructures work in wave attenuation of seabed sediment. Amplitudes of compression wave in sediment columns were measured point by point at the interval less than one wavelength in the study; and it is shown that negative exponential function is a type of acoustic attenuation model for sediment in its full length. Data of wave attenuation of seafloor sediments are mainly obtained by coaxial gap measurement method at present, but the sound attenuation model is not identified by using the method; so it is difficult to establish the relationship of results of wave attenuation of seafloor sediments taken from different sea areas. In this paper, an evaluated R, which result from the ratio of the amplitude inversed by the sound absorption coefficient divided by the ratio of the amplitude inversed by the sound attenuation coefficient (the ratio of two amplitude ratios), is proposed to be an evaluation criterion. After the data analysis of sound attenuation of seabed sediments from the South China Sea, which were obtained with measurement method of sound attenuation between the gap along the vertical axis, it was found that the evaluated R’s of sound attenuation from part of the sediment samples were much larger than one and their sound attenuations did not meet the exponential function of negative index. Under the conditions of the exponential function of negative index with which sound attenuation of seabed sediments was satisfied and in comparison with the evaluated R’s of sound attenuation of seabed sediments from the South China Sea predicted with Hamilton's empirical formula of sound attenuation and frequency and the ones measured with acoustic probe in our project, it was found that the range of ratios of sound attenuation of seabed sediments from the South China Sea can be predicted by Hamilton's empirical formula of sound attenuation and frequency. The advantage of measurement by the acoustic probe is in both accessing acoustic attenuation data and identifying sound attenuation model of seafloor sediments, and then the relationship of measured sound attenuation of seafloor sediment from different sea areas can be established with their evaluated R’s.

Key words: seabed sediment, small distance, small scale sample, acoustic attenuation, acoustic attenuation measurement