Method and apparatus for measuring visibility from the polarizat

Optics: measuring and testing – By particle light scattering – With photocell detection

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356364, G01N 2121

Patent

active

043623875

ABSTRACT:
A method and an optical sensing apparatus (1) are disclosed for measuring the polarization properties of light being scattered in the sky to obtain an accurate indication of visibility. The intensities (I.sub.1 and I.sub.2) of two linearly polarized components of the daylight are measured, so that a polarization ratio (P) can be calculated to provide a visibility index by which visual quality and visual range can be determined. The present method and apparatus may be extended to determine plume blight by comparing the polarization properties of light scattered by the plume with the polarization properties of the background sky, whereby theoretical visibility models may be validated. In an alternate embodiment, another apparatus (30) may be utilized with a sensing system (46) that employs polarization modulation techniques, so that the polarization properties of the entire sky can be measured in the ultraviolet and infrared regions of the electromagnetic spectrum. Accordingly, indications of both gas phase and particulate pollutant distributions in the atmosphere can be simultaneously determined depending upon the magnitude of the polarization ratio (P) in regions of atmospheric pollutant absorption.

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