典型浅海温跃层内波对声场起伏的影响

The fluctuation of sound field due to internal waves on the thermocline in typical shallow water

本文描述了在夏季典型海区，温跃层内波起伏和不同距离声振幅起伏的实验测量结果。温度起伏记录时间48．96h，温跃层厚度约2－4m，温差达10-15℃。等温线内波垂直位移有5－6m，且主要受最低阶模式支配。测量获得的内波垂直空间频谱特性中，除潮周期占主要成分外，0．05-0．143cpm（7－20min）之间有明显的谱峰，谱衰减系数在－1．5-－1．7之间。数值计算表明内波相、群速度在低频段完全相同，均为0．329m／s；随频率增加，相、群速度从约0．03cpm（33．33min）开始分离，且群速度值下降更快。在不同距离接收点，声振幅信号起伏有8-10dB；随距离增加，起伏有加快的趋势，并伴有信号衰落现象。谱衰减系数在－1，45-－2之间。最后，用PE算法，模拟计算在内波起主导作用下的声振幅起伏。

Abstract: In this paper, the results of experiments concerning the fluctuations of internal waves on the thermocline and the fluctuations of sound amplitudes at the different range in typical shallow water are presented. Recorded time is 48.96 hours. Thickness on the thermocline is about 2-4 m. The deviation of temperature recorded at the fixed depth has 10-15℃. The vertical displacements of isotherm curves are about 5-6 m, which are dominated by the lowest mode. The measured spectrums of vertical displacement have obvious spectral packet at the range of 0.05 cpm (20 min) and 0.143 cpm (7 min) besides diurnal and semidiural tide frequency bands. Spectrum attenuation coefficients are between -1.5 and -1.7. Numerical calculation shows that phase speed and group speed of internal waves are equal to 0.329 m/s at the range of lower frequency. And with the increasing of frequency, group speed drops more quickly. The measured fluctuation of acoustic amplitude is about 8-10 dB. With the increasing of ranget the fluctuation trends to be faster and acoustic signals are declining. Spectrum attenuation coefficients are between-1．45 and-2． At last， PE method is used to simulate the acoustic amplitude fluctuation，in which internal waves are the important element．