Research On The Inversion Method Of Aerosol Materials' Optical Constants

As a basic physics characteristic parameter, the optical constant of particle material, is the foundation of calculating the radiative transfer problem for a cloud of particles, which plays a very important part on studying the aircraft's infrared stealth by making use of aerosol.This paper is to study the inversion method of optical constants for particles that have an'μm'size. After comparing and analyzing some common methods home and abroad, the research idea of this paper is brought out: Under the premise of the independent scattering, based on Mie theory and K-K relation, we can inverse the optical constants of particles from the transmittance, by knowing the radius, concentration and thickness of the particle system beforehand.Here, the Monte Carlo method, which is a method relied on probability, is introduced to simulate the transmittance. By testing, a Monte Carlo programme in matlab language is fulfilled to determine the transmittance, reflectivity and absorptivity, through a 1-dimension infinite flat (a media layer being consist of particle system) with certain radiation parameters and thickness. Comparing with some related references home and abroad, this method shows it's reliable. Then, the transmittance spectra of Graphe KS-2, Magnetite and Hematite particles are worked out by using Monte Carlo Simulation. On one hand, we can analyze the extinction effect caused by concentration, radius and materials, and on the other hand, we get the"experiment"transmittance for the inversion.A matlab inversion programme for determining optical constant of particles is fulfilled based on Mie theory and K-K relation. In the process of Simplifying and verifying the K-K relation, some suggestions are given: when computing the real part from the image part, in order to avoid zeros in den of the Cauchy integral term, the image part is necessary to be re-constructed; and also the image part is better to be extended to all the wavelength by a reasonable presume; and setting the interval of adjacent wavelength equivalence can prevent the result from distorting locally. Throughout the inversion,κ(λ) are variables, by calling the optimization function'lsqcurvefit'in matlab, the Levenberg-Marquardt method is used to fit the transmittance spectra. And when the error comes to a minimum value, we can get the best solutions. No matter how to initialize the variables, the final result always is the only, which tells this inversion method is feasible.By knowing the transmittance spectra of the three particle materials, we work out their optical constants. Comparing with the references, they agree well. As a result, the research method used in this paper proved to be reliable.