| Clouds are visible polymers of small water droplets and ice crystal particles suspended in the atmosphere.The study of size,shape,phase and other microphysical characteristics plays an important role in revealing the development process of clouds and the formation mechanism of precipitation,as well as weather modification.However,the current detection methods cannot meet the needs of size measurement,phase discrimination and shape recognition of ice crystal particles,simultaneously.Interferometric particle imaging(IPI)is a measurement technology based on the theory of particle scattering.Preliminary measurements of spherical droplet and non-spherical ice crystal particles have been achieved by using this technique.However,the high precision measurement of multi-disperse spherical particle fields and non-spherical droplet particles are rarely involved.Besides,the current research is only proceeds in the laboratory.In view of the above problems,this paper mainly makes the following research:1.Based on optical transfer matrix theory,the scattering light of particles is analyzed.The imaging and measurement principle of both spherical and ellipsoidal particles are introduced.The parameter calculation method of IPI optical system is given.2.An iterative mean filtering(IMF)algorithm with the function of gross error elimination is proposed.The filtering effect of the interference image with different TC is simulated and the range of the TC is analyzed.The relative measurement errors of particles with diameter of 21.3μm,45μm and 57.9μm and the multi-disperse spherical particle field are 2.56%,0.99%,2.84%and 5.11%,respectively.Therefore,the precision measurement of particle size of monodisperse and multi-disperse spherical particle field is presented.3.The scattering characteristics of ellipsoidal particles are studied.A method of judging the orientation of ellipsoidal particles through the interference in-focus or out-of-focus images is proposed.The Lighttools model is established to study the relationship between particle orientation and the distribution of the in-focus image.The relationship between the emitting points,the speckle orientation of the out-of-focus image and the distribution of the in-focus image are researched through Matlab simulation.The orientation of the ellipsoidal particle can be obtained by doing the vertical axis symmetry of the glare point distribution of in-focus image,or by doing the perpendicular line of the speckle orientation of out-of-focus image,and then do vertical symmetry.An IPI system is built to verify the correctness of the above method.4.A method for determining the speckle orientation by autocorrelation or Fourier transform of the interference out-of-focus image is proposed.The electric field intensity of the speckle image is studied theoretically to reveal the slope relationship between the distributions of the speckle and its autocorrelation and Fourier transform results.We found that the orientation of the autocorrelation of an out-of-focus image is consistent with the speckle orientation of the image.Further,the orientation of the Fourier transform of an out-of-focus image is perpendicular to the speckle orientation of the image.The correctness of the conclusion is verified by simulations and experiments.5.The cloud particle measurement system based on IPI technology is designed.The scattering angle of the system is determined to be 90°.The IMF algorithm is modified and the system testing is completed through standard particle measurement in the laboratory.The 70m~3 expansion cloud chamber is used to generate warm cloud particles by spraying and expanding method.The cloud particle measurement system is used to obtain the out-of-focus images and realize the measurement of the particle size spectrum distribution of warm clouds in cloud chamber. |
