Inversion of Light Scattering Measurements for Particle Size and Optical Constants

Jones, Matthew R.

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https://hdl.handle.net/2142/72240 Copy

Description

Title

Inversion of Light Scattering Measurements for Particle Size and Optical Constants

Author(s)

Jones, Matthew R.

Issue Date

1993

Doctoral Committee Chair(s)

Brewster, M.Q.,

Department of Study

Mechancial Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Engineering, Mechanical
• Physics, Optics

Abstract

• Light scattering techniques have proven to be valuable tools in determining the size and optical properties of aerosol particles. Laser light scattering techniques can be used unobtrusively in harsh environments, so the development and improvement of these techniques is of great interest. The primary difficulty associated with light scattering techniques is inverting the data or obtaining the desired information from the measurements.
• The mathematical formulation of the light scattering problem results in a linear inverse problem with discrete data. Solution techniques for this class of problems are classified as either analytical or empirical. In this study, the inverse light scattering problem was solved for the particle size distribution function (PSDF) and the optical properties of the particles using a combination of analytical and empirical techniques. Using synthetic data sets, it was demonstrated that the inversion technique is capable of inverting measurements of the light scattered by a weakly absorbing sphere. The technique was also used to retrieve the PSDF and refractive index from synthetic measurements of the light scattered by log normal distributions of non-absorbing spheres in a blind test. Attempts to retrieve the PSDF were unsuccessful when the distributions were broad, but the refractive index was accurately retrieved in all cases. The results of this study indicate that because of the ill-posed nature of the inverse light scattering problem, constraints based on a priori information regarding the unknown PSDF must be available to successfully apply the analytical inversion technique. If such information cannot be obtained from analysis of the experiment or use of the empirical method, the complementary use of collection techniques is recommended.
• Light scattering measurements at 15 polar angles were obtained using a multichannel polar nephelometer. A calibration procedure for absolute scattering measurements and the use of the nephelometer are described. The light scattered by polystyrene spheres and by Al$\sb2$O$\sb3$ smoke particles was measured and inverted. The results of these experiments demonstrate that the inversion technique developed in this study is a practical method of analyzing aerosol particles.

Graduation Semester

1993

Type of Resource

text

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http://hdl.handle.net/2142/72240

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