水下声信号的激光干涉测量

为准确测量水下目标的发声频率,在光学暗室下建立了基于激光干涉法探测水下目标的实验系统。当水下声源引起水表面波动时,用激光照射水面,携带声波信息的水面散射光与参考光干涉,利用精密光学测量装置探测光程差的改变,通过数据采集和处理系统从干涉信号的频谱分析图中解调出水下声信号的频率信息。干涉信号的频谱分析图中存在以水下声信号频率为中心的频带,频带宽度与自然水表面波引起的多普勒频移有关。实验结果表明,水下发声目标引起水表面波动的振幅在纳米级,系统可以实时探测出4～15kHz的水下声信号,且测量标准偏差7Hz。该系统可满足水下目标识别技术的实时性、准确性等要求。

Laser interferometry of underwater acoustic signals

A laser interferometric method is proposed to detect the audible frequencies of underwater acoustic signals. A laser beam is used to irradiate the air-water interface when an underwater acoustic source causes the fluctuation of the water surface, the scattered beam with acoustic wave information will interfere with a reference beam according to the principle of the Michelson interferometer,and the frequencies of water surface waves can be concluded in the interference results.A precise optical detection device is used to detect the change of optical path difference caused by the water surface fluctuation and to achieve the real-time information concerning audible frequency of the underwater acoustic source by demodulating the data in processing system. It can be seen from the real-time frequency-domain graphs that the central frequency of the frequency band is the audible frequency of underwater acoustic signals, while the low-frequency band results from the Doppler shift caused by the natural fluctuation of the water surface.Experiment results prove that the method can be used to detect real-time underwater acoustic signals with the frequency from 4 kHz to 15 kHz and the test error is less than 7 Hz.These results can meet the requirement of the underwater acoustic signal detection for the real time and precision.