Detection Of Underwater Bubble Field Based On Digital Holography

The detection of the underwater bubble field is an important mean to study the characteristics of the wake.The physical model of the wake can be established by analyzing the distribution of the bubble field,and then used to analyze the shape and motion characteristics of the ship.It has some huge advantages over other detection methods to use digital holographic means to detect the underwater bubble field.Digital holography combined with image processing and digital reproduction technologies can reconstruct the bubble field digital hologram,and obtain the three-dimensional position information and radius of bubble to realize three-dimensional reproduction of bubble field.In this paper,the bubble field was simulated and experimented based on the theory of digital holography.Based on the Fresnel diffraction integral algorithm and the Mie scattering theory,we analyzed the influence of the recording distance and the bubble size on the digital hologram digital hologram and the single-bubble digital hologram by using the physical model of the digital holography of the underwater bubble field.And then the simulation and reproduction analysis of the multi-bubble digital hologram were carried out without considering the scattering between bubbles.Finally,the digital holographic image of the bubble field was obtained by using the Matlab Graphical User Interface to set the CCD and bubbles parameters.The ideal digital field image of the bubble field was obtained using the self-built experimental system.Bubbles were generated in the water tank,and then packaged and storaged by a special slide.The digital holographic image of the bubbles in the slide was accquired using a single optical path and Mach-Zendel optical path.Then,we conpared and analyzed the two resules.Three-dimensional reproduction of the bubble field was reproduced according to the bubbles parameters reconstructed by the digital holographic image of the bubbles.The noise of the image of the bubbles was suppressed by frequency domain filtering,and the contrast of the image was enhanced by the gray scale equalization.The focus of the single bubble was selected according to the three fast Fourier transform algorithm and the focusing algorithm.Depending on the focused position of the single bubble the one dimension information of the single bubble was achieved.Then,the edge recognition of the bubble was performed using the focused image,and the other two dimension information and the radiu of the single bubble were calculated.Thus,we succeeded the three-dimensional reproduction of the single bubble.Based on the theory to treat a single bubble,the three-dimensional information and the radiu of each bubble in the multi-bubble field could be obtained by using the rectangular template to intercepting its own image.And the three-dimensional reproduction of the multi-bubble field was accomplished through the software to integrate all bubbles information.