中国近海悬浮颗粒物海水声波衰减

Sound attenuation in suspended particulate matter seawater of Chinese sea offshore

在对颗粒物声吸收机理分析的基础上,根据已有的南黄海和莱州湾海洋调查数据,对中国近海实际海域悬浮颗粒物海水在声呐工作频段内的声波衰减进行了计算分析。结果表明,在悬浮颗粒物浓度高的海水区域内,悬浮颗粒物粘滞性声吸收所造成的声波衰减与不计及颗粒物存在的海水声吸收相比不可忽略。计算分析同时表明,在声呐工作频段内,颗粒物的散射声吸收可以忽略不计。取可使粘滞衰减为较大值的粒径为5μm的悬浮颗粒物海水进行计算,在低于几十千赫兹的频率范围内,当泥沙类悬浮颗粒物浓度高于0.1kg/m^3、有机类悬浮颗粒物浓度高于1kg/m^3,颗粒物粘滞衰减系数将大于清澈海水的衰减系数。泥沙类悬浮颗粒物海水浓度高于0.1kg/m^3、有机类悬浮颗粒物海水浓度高于1kg/m^3,可以作为是否需要计及颗粒物声吸收的比较保守的估计判据,或是作为悬浮颗粒物海水达到声学混浊的估计判据。

Based on the analyses of sound absorption mechanism of particles, the sound attenuation in suspended particulate matter seawater of real sea area is calculated and analyzed according to sea survey data of South Yellow Sea and Laizhou Bay. The results shown that, in the frequency range of sonar working, the sound wave attenuation produced by viscous absorption of suspended particulate matter can not be neglected comparing to the sound wave attenuation in clear seawater. It is know from calculation that scattering absorption of suspended particulate matter can be neglected in the frequency range of sonar working. Taking the partical radius as 2.5 μm, it can be obtained from calculation that the viscous attenuation coefficient will be higher than the attenuation coefficient of the clear seawater when the concentration of the particles is higher than 0.1 kg/m^3 for the sediment-class suspended particulate matter and the concentration of the particles is higher than 1 kg/m^3 for the organic class suspended particulate matter in the frequency range lower than several kHz. So condition that the concentration of the particles is higher than 0.1 kg/m^3 for the sediment-class suspended particulate matterand and higher than 1 kg/m^3 for the organic class suspended particulate matter can be seen as a conservative criterion whether the existence and effect of the suspended particulate matter should be considered in the problem of seawater sound attenuation or not. The condition can also be considered as the basic requirment of acoustical turbid for suspended particulate matter seawater.