南海北部浅海声场起伏及统计特性

水下声场的时间积分声强和峰值声强是声呐检测中的重要物理量,而海洋中的内波等动力学过程会造成声场强度的起伏。对南海北部浅海内波环境下定点声起伏实验数据分析,结合数值仿真,总结了试验海域近海底发射和近海底接收条件下内波引起接收信号强度起伏的统计特性.分析结果表明:接收信号的时间积分声强起伏小于峰值声强起伏;时间积分声强与峰值声强起伏的概率分布与对数正态分布较为接近.时间积分声强和峰值声强起伏大小与信号的频率有关,同一收发距离,中心频率650 Hz信号的声强起伏较中心频率310 Hz和375 Hz信号的声强起伏更为剧烈。对于同一频率,当海底较平坦时,声强起伏的闪烁指数随传播距离的增加而增大;当水深随传播距离逐渐变深时,声强起伏规律受内波和水深变化共同影响而更为复杂,闪烁指数先随传播距离增加而增大,之后又随传播距离的增加而逐渐变小. 

The intensity fluctuations and statistical characteristics in the shallow water at the north of South China Sea

Temporally integrated intensity and peak intensity of the ocean acoustic field are key factors in sonar system,while the sound field will be fluctuated caused by the internal waves in the ocean.The statistical characteristics of the fluctuated sound intensity is concluded based on the experiment data analyzation in the shallow water at the north of South China Sea with fixed source transmitter and sound receivers along with numerical simulation.It is shown that the fluctuation of the temporally integrated intensity is smaller than the peak intensity;the probability distribution functions of the temporally integrated intensity and peak intensity are close to the log-normal.The fluctuation of the temporally integrated intensity and peak intensity is associated with the source frequency.The fluctuation at the center frequency of 650 Hz is higher than the result at the center frequencies of 310 Hz and 375 Hz.For the same frequency,the scintillation index of the sound intensity increases as the source-receiver range increases when the ocean bottom is flat.The fluctuation of the sound intensity is more complicated when the sea depth become deeper as the source-receiver range increases at a fixed frequency.In this case,the scintillation index of the sound intensity increases at first and decreases after certain range as the source-receiver range increases.