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Optical Engineering

Extinction By Clouds Consisting Of Polydisperse And Randomly Oriented Nonspherical Particles At Arbitrary Wavelengths
Author(s): Janon F. Embury
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Paper Abstract

The wavelength location of extinction spectra peaks for individual particles depends on their size, shape, and orientation. An aerosol cloud consists of many particles with a collection of sizes, shapes, and orientations. When electromagnetic radiation passes through a cloud, the individual particle extinction spectra add together, and the resulting extinction spectra for the particle ensemble become essentially flat. This occurs for particle sizes approximately on the order of and larger than the wavelength measured inside the particle. The flat spectra depend only upon particle size and shape distribution and are independent of complex refractive index. At particle sizes smaller than this, Rayleigh scattering and absorption takes place, and extinction spectral peaks will be observed for the particle ensemble in regions of anomalous dispersion. In the Rayleigh region extinction, when dominated by absorption, will depend upon particle shape distribution and complex refractive index but will be independent of size distribution. Metal particles have a complex refractive index that is strongly dependent on wavelength; however, for most other particles with weaker refractive index dependence on wavelength, there will be an inverse wavelength dependence in the Rayleigh absorption spectra and an inverse fourth power wavelength dependence in the Rayleigh scatter spectra.

Paper Details

Date Published: 1 February 1983
PDF: 7 pages
Opt. Eng. 22(1) 220171 doi: 10.1117/12.7973050
Published in: Optical Engineering Volume 22, Issue 1
Show Author Affiliations
Janon F. Embury, Department of the Army (United States)


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