An Underwater Microbiological Detection Method Based On Off-axis Digital Holography

Water is an indispensable natural resource for mankind and must be protected from pollution.Microorganisms in water are closely related to the water environment of their life.The information such as the type,quantity and activity of micro-organisms can directly reflect the ecological conditions of water environment.The monitoring and optimization of water environment are inseparable from microorganisms.The exploration of underwater microorganism is of great significance to the study of water environment.In this paper,an off-axis digital holographic underwater microorganism detection method based on Jamin interferometer is proposed to observe the microorganisms in water environment and collect statistics on the information of microorganisms,which is of significant value to water pollution control.And the experimental system and algorithm are designed to study underwater microbes.The dissertation studies diffraction theory and traditional holography,and the process of recording and reproducing digital holography.Then the optical path proposed in this paper is analyzed by modeling and its feasibility is verified.The characteristics and recording conditions of off-axis digital holographic reconstructed image are analyzed.Two kinds of digital holographic reconstruction techniques are introduced.The background noise of hologram recorded by camera is eliminated by double exposure method and the zero-order image is eliminated by the frequency spectrum filtering method.Gradient focusing and frequency-domain focusing are used to determine the focused position of the reconstructed image of the microorganism automatically,to obtain the edge-sharp image and the three-dimensional position information of the microorganism.The elliptic fitting method identification method based on least squares and the Euclidean distance discriminant method based on invariant moment were used to identify and extract the microorganism in the image and get the number of microorganisms in the target species.Finally,the density was calculated.The thesis verifies the feasibility of using off-axis digital holography system based on the Jamin interferometer for underwater microbes detection.The design of the algorithm and the construction of the experimental system are completed.The biological information such as the types,size,distribution of position and movement status of the microorganisms is obtained.to determine the quality of the water in a contactless,realtime and automatic method.