Millimeter Through Visible Frequency Waves Through Aerosols: Particle Modeling, Reflectivity and Attenuation

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Virginia Tech

This thesis addresses the problem of modeling atmospheric aerosol (such as haze and fog) particle-size distributions in order to predict the effects (such as attenuation and reflectivity) that these particles have upon the propagation of electromagnetic waves of micrometer range wavelengths. Specifically, an inversely proportional to the fourth power of the particle diameter model is used for haze and the gamma and lognormal distribution models are used for fog. In the case of fog the models are developed based on data consisting of measured fog particle-size distributions at five locations. In this relatively big amount of data, the gamma distribution model is an accurate fit for all the cases and, also, the resulted size distribution does not depend on the altitude. This leads to considerably simpler formulations which yield a linear relationship between the reflectivity factor and the liquid water content. The knowledge of one parameter appears to be enough for defining the model and subsequently predicting reflectivity and attenuation. Attenuation and reflection in haze are found to be insignificant for millimeter wavelengths and somewhat appreciable for the visible ones. In fog, attenuation is found to be extremely high for the infrared-to-visible wavelengths and very low for the millimeter ones.