A Study On Classification Of Suspended Particles And Marine Microalgae By Polarized Light Scattering

Identification and classification of marine microalgae is the basis of marine scientific research.The development of microalgae identification and classification is of great significance for us to grasp the microalgae information accurately,exploit and utilize microalgae resources better,prevent red tide and other marine disasters,and reduce or even avoid major economic losses.In this thesis,a method for the identification and classification of marine microalgae using polarized light scattering technique is proposed based on the existing non-polarization optical methods,combined with a mass of previous studies in the laboratory on polarimetric techniuque.Since polarized light scattering is very sensitive to the microstructure of scattering sample,we can obtain more information from polarization measurements than traditional optical methods.Polarization optics is also compatible with current optical methods without altering the optical path,therefore we can realize polarization measurements only by adding polarizing modulators in the current optical instruments.A large number of marine microalgae can be identified and classified quickly by using polarized light scattering methods.The following works are carried out in this thesis.A single scattering simulation method is established using sphere and cylinder as the scatterer.The influence of detection direction and incident polarization state on the recognition effect of the refractive index,shape and size of scattering particles is studied by simulation.It provides a theoretical basis for the design of the experimental device and the appropriate measurement conditions in the experiments.An experimental set-up for polarization scattering measurement is designed and built.Simultaneous measurement of the polarization components is realized by the method of amplitude division.By the design of the sample cell and the optical system,a measurement for phantom and marine microalgae samples one by one has been realized.It is close to the actual environment.The influence of the noises is reduced by choosing the appropriate digital filtering method,and the calibration method is developed as well.The Linear Discriminant Analysis(LDA)method is introduced in this work to display the experimental results visually and quantitatively.Meanwhile,a standard of the identification effect by the ratio of peak distance and average half height width is proposed.The particles with different refractive index or different shape have been measured using polarization scattering method.It shows the feasibility of polarization scattering method for identifying particles,and the influence of incident polarization state on the recognition effect.The identification experiments of both single and mixed samples of several marine microalgae were carried out under laboratory conditions,which showed a possibility of monitoring the quantity variety of the specific marine microalgae by polarization scattering.It is expected to provide technical support for early warning of marine red tide disaster and detection of growth status of marine microalgae.Based on the analysis of the experimental results,the idea of choosing the best incident polarization state with the best recognition effect is put forward.According to the particle experiments,we find a better incident polarization state in local and get the better recognition results.