Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Atmospheric Sciences (PhD)

Administrative Home Department

Department of Physics

Advisor 1

Raymond A. Shaw

Committee Member 1

Jeremy P. Bos

Committee Member 2

John Valenzuela

Committee Member 3

Michael L. Larsen

Abstract

A better understanding of light transport and scattering in turbulent clouds is needed for more accurate remote sensing, improved imaging and signal transmission through atmospheric aerosol and fog, and deeper understanding of cloud optical properties relevant to weather and climate. In this study, we investigate the impact of light scattering in clouds on two problems of atmospheric relevance.

In the first part, we examine deleterious effects of the atmosphere on remotely acquired images including signal attenuation and potential blurring due to forward-scattered light accepted by the imaging system. A prior proposed aerosol scattering model provides a method for calculating the contrast and spatial detail expected when imaging through atmospheres with significant aerosol optical depth. We compare modulation transfer functions obtained directly from images taken through a cloud chamber to those calculated from theory using measured cloud properties. We find that the significance of scattering-induced optical blurring depends sensitively on the properties of both the particles and the imaging system. The theoretical aerosol expression modulation transfer function capture the basic behavior of the system, with deviations likely a result of not accounting for broad particle size distributions.

In the second part, we investigate how clusters and voids in the spatial distributions of particles within a cloud cause light transport to deviate from the exponential extinction law. We explore both perfectly random and correlated scattering media with a Monte Carlo ray tracing program, and find that the degree of non-exponential attenuation can be characterized by the radial distribution function. Our numerical observations regarding direct, diffuse and backward radiative transfer are shown to be consistent with a previous “cloudlet” approach, providing a bridge between the analytical cloudlet model and continuous correlation function approaches. Finally, we numerically explore light propagation through turbulent clouds with polydisperse size distributions calculated by a large eddy simulation of the MTU Pi Chamber. We find that both the mean and standard deviation of direct and diffuse forward flux change when clustering exists, and make suggestions for future laboratory cloud chamber experiments to detect the presence of spatial correlation.

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