Research On Underwater Low Frequency Sound Source Based On Light Diffraction Method

With the continuous development of human society,limited land resources are consumed continually so that people pay more attention to ocean where store abundant resources gradually.Meanwhile,the development and utilization of marine resources encourage promote the improvement of submarine detection technique further.There are two kinds of common methods of target detection which are based on sonar technology and laser-acoustic remote sensing technology.Because of the advantages laser-acoustic remote sensing technology including high sensitivity,real-time non-damage detection and so on,this paper introduces the extraction of information of the sound sources which are come from water surface waves and lays the foundation for detection of submarine targets.This paper presents the studies on laser diffraction technology which is based on liquid surface wave.Through the diffraction pattern modulated by liquid surface wave,the technology could obtain the amplitude information of liquid surface wave and so on.Thus,the information on submarine targets could be gotten.Surrounding this topic,the research works as follows:(1)On the foundation of water wave theory,dispersion relation of liquid surface wave and wave equation which is relation to vibration of liquid surface caused by submarine acoustic source could be obtained,these conditions provide the theoretical basis for detection of submarine acoustic source through laser diffraction methods.(2)While the oblique incidence of laser to the surface of liquid,because of the perturbation motion,liquid surface wave could be regarded as phase gratings.It is not only all different orders speckles and angular breadth of zero-order speckle,but also the quantitative relationship between them and some factors such as incident wavelength,wavelength of liquid surface wave and so on could be gotten through grating equation.In addition,the diffraction patterns which are consistent with theory could be obtained by the experimental equipment of submarine detection.While the increasing of wavelength of laser or decreasing of wavelength of liquid surface wave,angular breadths of different orders speckles would increase.(3)The horizontal position of submarine low-frequency acoustic source also is investigated by laser diffraction technique which is based on liquid surface wave.The mechanism of detection of liquid surface wave and decay process of submarine acoustic wave propagation are analyzed.Because of the decay of sound wave and the difference between distance of waver and distance of acoustic source,therefore,the amplitudes of liquid surface wave obtained is different.During the process of experiment,the waver move along the perpendicular directions on the liquid surface and the relationship between amplitudes of liquid surface wave and moving distance would be obtained.The coordinate of maximum amplitude means the nearest distance between waver and acoustic source on the moving direction.Subsequently,the horizontal position of submarine acoustic source would be obtained through curves of transformation relation.(4)Because of the decay of submarine acoustic wave propagation and the difference of rate of decay of acoustic wave at different frequency,the relationship between decay of acoustic wave propagation and frequency is investigated by laser diffraction technique.When the waver moves along one straight line on the water surface,the degree of decay is different for the waves at different frequencies if the moving distances are the same.In addition,the rate of change of amplitude for liquid surface wave also is different.The higher frequency the submarine acoustic source has,the faster the rate of change of amplitude is.