Study On Reconstructing Methods Of Digital Hologram Of Underwater Bubble Field

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 thesis, 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 completed work mainly is as follows:1. Introduced the principles and characteristics of traditional optical holography and digital holography. Discussed the impact of the underwater environment on the bubble field detection, and advantages of digital holography in underwater bubbles detection compared to optical holography. Also introduced research background and research status underwater bubbles detection.2. Established the mathematical model of recording and digital reconstruction of digital hologram. Detailly analysed the theory of reconstructing algorithm in digital holography and the associated digital image processing methods.3. Discussed two different figures reconstruct ideas, Fresnel transformation and convolution. Completed the reconstructing program of digital hologram,and gained the corresponding results of the computer reconstruction. At the same time, discuss the digital image processing technology applied in the hologram reconstruction process.4. Applied the digital holography to the detection of underwater bubble field, Carried out experiment of recording of digital hologram of underwater bubble field, and completed reconstruction of digital hologram.5. Completed bubble identification, extraction and data statistics of reconstructing hologram. First, used the threshold extraction to eliminate background noise in the reconstruction plans in order to identify the bubble; followed by edge detection technique to extract air bubbles in the coke, in the process, separately used four different detected operators to extract the bubble, choose the optimal method for feature extraction. Then, calculated the size of the bubble by scanning method and reconstructing all aspects of the bubbles by using neighborhood reconstructing method, Finally, designed programs to statistics the number of bubbles automatically, the accurate rate of statistical results are reach to 91.2%, the effect is ideal.The thesis is well integrated underwater digital holography and particle field detection technology, completed a study of digital holography based work. Paper made theoretical analysis, computer simulations and experiments for future digital holography further in-depth study provides useful help and reference.