Three Dimensional Passive Acoustical Imaging System Using Hemispherical Array Detectors
A High resolution three dimensional passive acoustical imaging system is realized by using array detectors arranged hemispherically covering the object. Auto and cross power or bispectral analyses of the detected signals are carried out so that images of the distributions of power of single frequency component or coherence among three frequency components are obtained. One of the most significant features of the system is the ability to display high quality images of any desired cross sections of three dimensional noise emitting objects simply by the choice of parameters at the stage of image reconstruction. Three dimensionally high resolutions, for instance resolution volume of 3cm × 3cm × 5cm for waves at 10 kHz over the observation volume of 60cm×60cm×60cm, are achieved. An image is obtained within five minutes and it is displayed on a color TV monitor or printed out graphycally. Moreover, to obtain structures which are much smaller than the wave length a new image reconstruction process which uses the matrix correspondence between the detected hologram and the complex amplitudes of mesh points on the object’s surface is proposed. The system is a powerful means for precise analysis and control of noise sources.
KeywordsCoherence Sine Azimuth Acoustics Sonar
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