Measurement Of Low-Frequency Acoustic Parameters And Analysis Of Sound Speed Dispersion In Seafloor Sediment

Seafloor sediments as an important boundary of underwater acoustic field,its low-middle frequency acoustic characteristics have the important influence on the law of sound wave propagation and the sound field structure in shallow water,and have important application value in marine geophysical detection,Ocean acoustic field measurement and prediction,submarine burial acoustic detection and underwater acoustic communication.In this paper,the Jiaozhouwan beach was selected as the large scale low-middle frequency experimental site.And the low-middle frequency measurement equipment,the in-situ middle-high frequency measurement of the First Institute of Oceanography,State Oceanic Administration,were used to carry out the in-situ sound speed measurement.Acoustic equipment,such as signal generator and oscilloscope,were used to measure the sound speed of Jiaozhouwan seafloor shallow surface columnar sediment samples in the laboratory.The bending element shearing measurement equipment was used to measure the sound speeds of the Yellow Sea seafloor columnar sediment samples.And the physical and mechanical parameters such as porosity,density and particle size of fine grained sediments(Jiaozhouwan and Huanghai sediment samples)were measured.The correlation between the sound speed of sediment and the frequency is analyzed,and the results show that the higher the frequency is,the greater the sound speed become.When the frequency is lower than 1 kHz,the sound speed varies slightly(sound speed increases 3.2 %);when the frequency is between 1~20 kHz,the range of sound velocity become larger(sound velocity increases 7.0 %);when the frequency is greater than 20 kHz,the sound speed varies slightly and tends to be a fixed value(sound speed increases 3.0 %).The conformance degree between the measured data and the exponential fitting formula is the best,followed by the logarithmic fitting formula.Combining the Biot theory with the Buckingham theory,the correlation between the measured data and the theoretical model is analyzed,and the results show that: When the frequency is lower than 20 kHz,the tendency of the measured data is consistent with the tendency of the Biot model,but the measured sound speed value is lower than the predicted value of the Biot model.When the frequency is greater than 20 kHz,the measured data is in good accordance with the Buckingham GS model.Combined with the physical and mechanical parameters,the correlation between the measured shear wave speed and the GS model is analyzed,and the results show that: The prediction trend of shear wave speed,porosity,mean particle size and GS model is consistent.The burial depth of seafloor sediments has great influence on shear wave speed,while the measurement frequency(1~5 kHz)has less influence on shear wave speed.In this paper,the in-situ low-medium frequency(300 Hz~34 kHz)sound speed of Jiaozhouwan seafloor sediment samples and the laboratory medium-high frequency(25~250 kHz)sound speed are measured.The shear wave speed(1~5 kHz)measurement of the Yellow Sea seafloor columnar sediment samples is carried out.This paper analyzes the relativity between sound speed and physical properties of fine-grained sediments.and expounds the dependence of the sound wave speed and the frequency on the basis of the sound propagation theory.The study has some reference significance to enrich the acoustic theory of seafloor and to promote the deep research of low-frequency acoustic characteristics and dispersion characteristics in seafloor sediments.