为实现水下中低频声信号的探测识别, 通过研究水下多声源相干探测信号的特征, 理论上给出了相干探测信号频谱混叠情况下的特征表达式, 并提出了一种基于Hilbert变换的信号解调处理方法, 实现了水下多声源相干探测信号频谱混叠情况下各声源发声频率的解调.该方法将探测信号经过滤波平滑处理之后进行Hilbert变换, 得到信号的解析形式, 然后对解析信号模值的平方进行二次滤波平滑等处理, 分离混叠在一起的频带, 将得到的信号进行频谱分析, 根据频移值计算得到水下各个声源的发声频率.在光学暗室下搭建激光相干探测系统, 对2~6 kHz的水下声信号进行实验, 实验结果表明, 该方法可以有效分离探测信号中混叠在一起的信号频带, 并准确提取各水下声信号的发声频率, 频率提取重复性不大于2.5Hz.

In order to realize the detection and recognition of underwater acoustic signals, the characteristic expression of coherent detection signal under spectral aliasing was given theoretically, and a kind of signal demodulation method based on Hilbert transform was proposed by studying the characteristics of underwater multi-source coherence detection signals. Acoustic frequency demodulation of underwater multi-sources was realized in case of spectral aliasing. In this method, the Hilbert transform is carried out after filtering and smoothing processes to obtain the analytic form of the signal. Then, the second filtering and smoothing processes are carried out for the squares of the analytic signal modulo to separate the aliasing bands. After that, the spectrum of the obtained signal is analyzed. Frequency of each underwater acoustic signal can be calculated according to the frequency shift value finally. A laser coherence detection system was built in the optical darkroom, and the underwater acoustic signals of 2~6 kHz were experimented. The results show that the proposed method can effectively separate the signal bands that are mixed together in the detection signal, the accurately extract the frequency of each underwater acoustic signal, and the frequency extraction repeatability is not more than 2.5 Hz.