The Study Of Monitoring Equipment Of Micro/Nano Plankton Based On Digital Holographic Microscopy

Micro/nano plankton play an important role in ocean ecosystem.It is the material base and source of other higher marine organisms,and its richness and cell abundance is an important indicator to judge the healthy development of ocean ecosystem,like coral and mangrove forests and so on.Therefore,the new method and equipment for the research on monitoring micro/nano plankton is of great theoretical and pratical significance.This thesis aims at monitoring of micro/nano plankton with size from 5?m to 100?m based on the digital holographic microscopy(DHM)by achieving the large refocus depth range imaging,three-dimensional(3D)reconstruction and accurate recognition of the micro/nano plankton.And on this basis,a prototype machine of micro/nano plankton monitoring based on DHM was developed,and obtained primary results.The main research contents and achievements include:1.Comparing of different optical systems for DHM to determine the feasible configuration.A Gabor optical system,and a coaxial optical system,off-axis optical system,single-path optical system based on Mach-Zehnder interferometer configuration were built successively on the optical platform to record hologram of an USA resolution test chart and micro/nano plankton.The reconstruction quality,refocus depth range,phase retrieve,3D reconstruction and the ability to resist external vibrations of the above optical system were compared,and finally the coaxial optical system based on Mach-Zehnder interferometer configuration was employed in the prototype machine.2.The extending of refocus depth range has been studied.The expression of PSF on the refocus plane in the coaxial optical system based on Mach-Zehnder interferometer configuration was derived,so as to obtain the relationship between the refocus depth range of the DHM system and its optical parameters,which has been testified by the optical experiment of the USA resolution test chart.According to the relationship,a method based on a combination of wave front code(WFC)and bicubic extrapolation iteration(BEP)was proposed to extend the refocus depth range.3.The autofocusing of multi-focus micro/nano plankton and refocus images fusion were studied.To solve the problem of small dimension and large quantity of micro/nano plankton,and large noise of hologram,an autofocusing method was proposed in which the micro/nano plankton were selected first and then calculated by an area focus measure;To reduce the high-frequence fringes around the micro/nano plankton and speckle noise inside the micro/nano plankton,an improved wavelet-based image fusion method based on a marked map was proposed.At the same time,deep learning was applied to the autofocusing of multi-focus micro/nano plankton and refocus images fusion,and obtained the outcome expected.4.3D reconstruction of micro/nano plankton was studied.The scanning electron microscope(SEM)based on scanning imaging,the phase imaging,the height-gray reconstruction,the amplitude tomography and the optical diffraction tomography based on holographic imaging were investigated and compared.The amplitude tomography was employed as the 3D reconstruction method in this thesis since it is more suitable for on-site monitoring.To solve the problem that contours of the front half of the micro/nano plankton can scarcely be recognized,and there are a lot of out-of-focus images in the refocus image,an improved amplitude tomography method was proposed to take measures on hardware and software.Finally,clear contours of the whole micro/nano plankton were obtained,thus to render the 3D imaging.5.Recognition of micro/nano plankton was studied.Both of the traditional machine learning and the deep learning were used in the recognition of micro/nano plankton.In the machine learning,traditional features and HOG features of micro/nano plankton were selected to train the SVM.In the deep learning,a Faster-RCNN was used to perform the selection of features of micro/nano plankton and the training of itself.6.A prototype machine for micro/nano plankton monitoring based on DHM was developed.The optical system was designed according to the key optical parameter,the selection of optical elements and its mounting bracket and,then its adjustment was finished;The control circuit was designed acording to the workflow of the machine,which controls the opening and closing of laser and image sensor,and the running of micro-fluidic system;The software of analysis of micro/nano plankton with the prototype machine was developed according to the requirement of the setting of the image sensor and the displaying of results,so as to to call the algorithms of digital reconstruction,autofocusing,image fusion,three-dimensional reconstruction and recognition model,and to save and display the results.The prototype machine has been tested preliminarily and obtained the outcome expected.