The Research Of Underwater Particle Field Detection By Digital Holography

Digital holography,digital recording of hologram and numerical reconstruction of the wave fields, offers an alternative recording and reconstruction in holography. The hologram generated by object is recorded directly by CCD and stored digitally by computer, and then reconstructed numerically. Combined with the advantages of digital feature of computer and three-dimensional image of holography,digital holography has good prospects in optical metrology and has been widely applied in various fields of science, engineering and biomedicine. In many fields of science and technology, it is very important to acquire the size, position and velocity of particles or droplets. There are plenty of techniques to get these parameters. Of all the techniques, optical holography has some particular advantages: non-destructive, wide size-range of the measured particles, large depth of field, direct reconstruction of 3-D particle field and high resolution.In this paper, digital holographic technology is used in underwater particle field detection successfully. On the basis of theoretical analysis of digital holography, the preliminary study carries out through computer simulation and experiments. The main work is as follows:1. The principles of optical holography and digital holography are introduced. The mathematical model of digital holographic recording and reconstruction is made. Besides, the theories such as recording digital hologram, numerical reconstruction and the related digital image processing methods are analyzed. Introduce the impacts that are brought to the holographic recording in the underwater environment. The advantage of digital holography in the usage of underwater detection is also explained.2. Two different digital reconstruction approaches are represented, i.e. Fresnel transform method and envelope method. Programs of recording and reconstructing hologram are developed. Planar object and ideal 3D object's digital holograms are done through computer simulation, by using numerical reconstruction method the object images are obtained successfully.3. The serious recording limitations due to the finite of CCD are discussed detailedly. After analyzing the experiment, the author completes designing the experiment in which hologram is recorded with CCD. Digital holograms of underwater physical and underwater bubble field are recorded in the experiment. And the image of the objects is successfully reconstructed from hologram with the program.On the organic combination of digital holography and underwater particle detection, this thesis completes the preliminary study on digital holography. The theoretical analysis, computer actual experiment offer the beneficial help and reference for the further study.