A Study Of The Dual-probe Method For Measuring The Acoustic Properties Of Seafloor Sediments

Submarine sediments are the lower boundary of the ocean sound field,which affects the sound field of the ocean.Easy and accurate access to the acoustic properties of seafloor sediments is one of the most important aspects of marine research.Currently,there is a lack of laboratory measurement techniques for sediments that can be used to measure the acoustic properties of sediment layered areas.In order to improve the accuracy of the sediment layering measurements,the original dual-probe method was optimized after the different measurement methods and the factors affecting measurement were analyzed.The optimized measurement method was applied to the acoustic measurement of the stratified areas of the sediment and analyzed the measurement accuracy of the method.Finally,it was applied to experiments on the effect of temperature variations on the acoustic properties of sediments.The specific research work carried out is as follows:(1)Study of the effect of the diameter size of the sampling tube and the inter-probe blockage on the measurement results of the dual-probe method by means of COMSOL Multiphysics finite element software.The simulation results show that the diameter of the sampling tube and the effective measurement range in the tube are positively correlated.When the measurement distance exceeds the effective measurement range,the amplitude of acoustic wave obtained by the probe will be high.Blockage between probes causes decreased amplitude of the sound wave obtained by the blocked probe.This effect is related to the distance between the probes and the distance between the blocked probe and the sound source.(2)The zero sound time of each probes and the sensitivity calibration coefficients of probes are obtained by the calibration of experimental equipment under current laboratory condition.Experiments were designed to study the influence of the diameter of the sampling tube and the barrier between the probes on the measurement results of the dual probe method.Experimental results show that 110 mm is the optimal sampling pipe diameter under the current laboratory conditions and its effective measurement range is 280 mm.In addition,the barrier correction coefficients of R2 probe under different barrier conditions are obtained,which provides a basis for calculating the acoustic characteristics of sediment stratified area.(3)The acoustic characteristics of the stratified area of the sediments were measured by dual probe method and the acoustic characteristics of sediments as a whole were measured by transmission method.The accuracy of the double probe method was judged according to the measurement results of the double probe method,the transmission method and the physical characteristics of the sediment.The results show that the dual-probe method can effectively measure the acoustic characteristics of sediment stratified region.The acoustic characteristics of sediment under temperature change were studied experimentally,which showed that the velocity of sample and the of velocity water increases along with the rise of temperature,the ratio between them in the vicinity of 1.0 fluctuations,samples of acoustic amplitude value and water acoustic amplitude value is reduced along with the rising of temperature,acoustic attenuation value fluctuates up and down along with the rise of temperature.