On the information content of linear and circular depolarization signatures of bioaerosols

Abstract

ABSTRACT Cao et al. 1 published a paper where differentiating bioaerosols (po llens) appeared feasible when linear depolarization ratio signature at multiple wavelengths could be obtained. The measurements were performed at 4 wavelengths. The bioaerosols were disseminated in a controlled environment and the discrimination analysis was based on Mahalanobis distances. Poor discrimination was obtained for single wavelength measurement while acceptable and good discrimination was reported for two and three wavelengths. Th is innovative work has raised the following question: to which extent does the addition of circular polarization sign ature to the existing linear polarization increase the overall discrimination capability? In order to answer that question, the measurements of Cao et al. were repeated for linear and circular depolarization ratios. We demonstrate experimentally that th e linear and circular depolarization ratio s are related to each other via a known simple theoretical mathematical expression in the case of randomly oriented particles. Hence, by measuring one, you obtain the other and consequently there is no additional information that is gained by doing measurements with the two polarization states. This suggests that there is no ne ed for full Mueller matrix measurement systems for detection and discrimination of bioaerosols. Keywords