Simulation Research Of Acoustic Imaging With Ocean Ambient Noise

Ocean ambient noise has always been considered as useless background noise to conventional sonar system. For this reason, active system or passive system will be disturbed by ocean ambient noise. However, for ocean ambient noise acoustic imaging, the noise itself can be used to detect targets and obtain visible images of the targets. Essentially, it is a passive detection system which is similar to the imaging in the atmosphere with optical cameras. The advantage is that no large power source is needed for the emission of acoustic signal. Instead, the scattering sound of the target to the ambient noise source can be used and even the imaging performance can be improved by its reflection and multipath effect.This paper aims at the preliminary simulation study on ocean ambient noise acoustic imaging theory and wave theory is applied to analyze the visibility of scattering sphere in different levels of anisotropic noise field. First, the Green's function for point source is created so as to spread the point source on an infinite sphere as the noise acoustic source. The distribution angular is varied to produce different levels of anisotropic noise field. Then end fire line array is used as acoustic lens to simulate and analyze the visibility of single array element and line array to the target. Finally, based on the simulation analysis and actual situations, preliminary design for ocean noise imaging experiment is discussed. The influence of main parameters of reflector as acoustic lens and receiving array to the noise imaging performance in the experiment is studied, which includes the size of the aperture and radius curvature of the reflector, the focal distance and gain of the reflector, material used for the reflector surface, the size of receiving array and the number of array elements needed. These parameters are also estimated and the applicable range in actual situations is presented.