Evaluation of an Analytical Model for Predicting Light Scattering from Cylindrically-Shaped Objects in the Ocean
TENNESSEE STATE UNIV NASHVILLE DEPT OF PHYSICS MATHEMATICS AND COMPUTER SCIENCE
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The polarization state of light in the ocean can be used to enhance visibility. We are investigating the consequences of scattering from non- spherically-symmetric particles on light propagation and visibility in the ocean. To calculate scattering from non-spherical marine micro-organisms, it is usually necessary to resort to approximate methods. One promising approximation is the coupled-dipole approach in which an arbitrarily-shaped object is divided into a number of identical elements arranged on a cubic lattice. Each element is treated as a spherical, dipolar oscillator with its polarizability specified by the real and imaginary parts of the index of refraction. Interactions between dipoles are included by determining the field at a particular dipole due to the incident field and the fields induced by the other dipole oscillators. The scattered field is then the sum of the fields due to each oscillator. The coupled-dipole method is promising because, in principle, an organism of any shape can be modelled, and all sixteen elements of the scattering matrix calculated. We have applied this approach to calculate scattering from spherical particles to verify the limits of the approximation, and from other shapes to investigate the effects of non-sphericity and chirality on scattering. In particular, we calculated all 16 Mueller matrix elements for the scattering from a finite cylinder, a single-sd helix, 14-strand helix, and ensembles of these particles. The effects of pitch, size, wavelength, and complex index of refraction were investigated. The results provide insights into the magnitude and type of depolarization effects associated with various marine microorganisms containing these structures.