Experimental Study On Underwater Acoustic Signals Based On Laser Coherent Detection

In this paper, the underwater sound field is simulated and experimental studied byusing laser coherent detection. Above all, simulation program is made by Matlab softwareaccording to the principle of underwater acoustic vibrations. The detection to natural waveof water surface without underwater acoustic signals and with underwater acoustic signalsof different frequencies are simulated respectively. Furthermore, an experimental deviceadopting fiber laser coherent detection is designed, and underwater acoustic signals arestudied experimentally. Finally, the extraction method in regard to low-frequencyunderwater acoustic signals is discussed.Natural wave of water surface is detected and researched experimentally in this paper.We also study experimentally different state of underwater sound field respectively, forexample, the sound source with different vibration frequency and acoustic vibration indifferent depths under water. Experimental results show that:(1) The underwater acoustic signal is simulated by Matlab software and the modelof laser coherent detection on fluctuations in the water surface caused byunderwater vibration source is established. By this model, it reveals the law ofacoustic vibrations, and it provides the theoretical basis for the experimentabout using laser coherent to detect underwater acoustic signals.(2) The characteristics of natural fluctuations on the water surface are studiedexperimentally by using laser coherent detection. The information of naturalwave of water surface are analyzed and the results show that the frequency ofnatural fluctuations on water surface is between9~25Hz. The results isconsistent with the experimental detection results that the time interval of theneighbored resolute points, which is20~60ms.(3) The underwater acoustic signals of different frequency and intensity aredetected by using laser coherent detection. The results show that underwatervibration can be detected effectively by this system when its frequency isbetween100~10000Hz. With the weakening intensity and increasing frequency of signal, the detection effects of the system on underwater acoustic signalstend to be worse.(4) The underwater acoustic vibration signals of different depths are researchedexperimentally by using laser coherent detection. The results show that theacoustic signals generated by vibration source at different depths becomeweaker with increasing depth of vibration source.The detection optical path of experimental system is connected by optical fiber. Itreduces the difficulty of adjusting system, and the anti-interference capability of thesystem is improved.