Study On The Laser Interferometric Detection Of Underwater Acoustic Signals Based On Wavelet Transform

More than three-quarters of countries in the world is bordered by the ocean. With the exploitation and utilization of land resources, many resources are on the verge of exhaustion, so different countries are competing for the abundant resources in the ocean. However, ocean exploration has gone deep into about ten thousand meters under the sea, so traditional sonar technology is difficult to meet the requirements of underwater target detection. How to quickly and accurately extract the information of underwater targets is a key issue to detect underwater targets. The paper has studied the principle of laser interferometric detection technique and applied wavelet transform tools to process the underwater acoustic signals for estimating the frequency and amplitude of the surface acoustic wave. The experimental platform based on the basic principle of laser interference detection has been set up, and related research work is as follows:(1) This paper introduced the theory of water surface acoustic wave and the basic principle of laser interference and proved that the motion of the surface particle of the water meter is a sine wave motion in the ideal situation. In addition, it is found that when the underwater acoustic source signal is generated, the vibration of the underwater sound source will cause the vibration of the surface of water meter. Therefore, the water surface scattered light and reference light carried underwater acoustic wave information. Furthermore, the paper proposed a method of laser interference detection of underwater acoustic signals, and the accuracy of this method was verified by a large number of simulation experiments.(2) In this paper, a new method is proposed to estimate the frequency of underwater acoustic signals based on wavelet transform. By analyzing the characteristic of time frequency distribution of laser detection signals of underwater acoustic signal, we discovered the regularity for wavelet ridges distribution of laser interference signal. According to this regularity, an experiment was carried out for estimating the instantaneous frequency of underwater acoustic signal using wavelet ridges. Furthermore, the demodulation method of water surface acoustic wave interference signal is designed by Mach-Zehnder interferometer.(3) The experimental platform based on the principle of laser interference was set up. This paper briefly introduces the water acoustic signal detection system which includes the underwater acoustic signal generation unit, optical path design unit and data acquisition unit. The experimental results of underwater acoustic signal in low frequency band and high frequency band display that frequency node error is less than 0.25%, and shows that the method of estimating underwater acoustic signals based on wavelet ridge point distribution of acoustic signal instantaneous frequency characteristics is effective.In summary, a method was put forward for estimating the instantaneous frequency of underwater acoustic signal using wavelet ridges, and the detection experiments using this method were carried out. The results proved the effectiveness of this proposed method.