POSTER Session 2

MORPHOLOGY CORRECTION TO COCCOLITH DEPOLARIZED FORWARD SCATTERING

We present a method to evaluate the effect of morphology on the depolarization of forward scattering by randomly oriented coccoliths of various species. As a first approximation, the depolarization by coccoliths can be approximated by a calcite disk of uniform thickness. In reality the thickness of each type of coccolith varies substantially as a function of radius. The optical axis of the crystal structures composing the interlocked elements of the coccolith also alternates between being normal or parallel to the surface of the crystal. The depolarization in a crystal is a function of the optical path length difference between the extraordinary and ordinary ray. This path length difference is a function of the thickness of the crystal, the angle of incidence of the light and the angle of the optical axis with respect to the surface. If the depolarization was a linear function of the optical phase difference between the ray it would be relatively straightforward to average over thickness and use a single mean parameter as a correction factor. However, the depolarization dependence involves the square of the phase difference which makes the result much more sensitive to the actual shape and crystal composition of the coccolith. For randomly oriented ensembles of coccoliths we have derived approximate formulas that can be used to evaluate the size independent corrections that need to be applied to the Young and Ziveri coccolith mean relative thickness estimates to obtain a properly corrected depolarization factor.

Georges Fournier, DRDC Valcartier Research Center, Canada

Qiming Sun, Ghent University, Belgium

Griet Neukermans, Ghent University, Belgium

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