US 4,362,387 A · Method and apparatus for measuring visibility from the polarization properties of the daylight sky

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.

Claims22

Dependent claims

A method for determining visibility of the atmosphere comprising the steps of:

measuring the intensities of two linearly polarized components of scattered daylight, said two components being respectively oriented perpendicular and parallel to a first plane containing the sun, an observation point, and a volume of the atmosphere under investigation,
aligning a light intensity measuring means from said point of observation towards said volume at an observation angle of approximately 90.degree. away from a vertical plane including the sun and said point of observation for measuring the intensities of said two linearly polarized components, and
comparing said two intensities to one another, the greater the intensity of the polarized component of daylight perpendicular to said first plane relative to the intensity of the polarized component of daylight parallel to said first plane, the better the visibility of the atmosphere.

A method for measuring visibility at an arbitrary region of the atmosphere from the polarization properties of the daylight sky, said method comprising the steps of:

aiming a light-collecting means at the region of the atmosphere to be investigated, said collecting means receiving electromagnetic signals that are representative of two linearly polarized components of the daylight, said two components being respectively oriented perpendicular and parallel to a plane containing the sun, an observation point, and the arbitrary region being investigated,
polarization-modulating said electromagnetic signals received by said light collecting means for converting said signals into an intensity modulated beam of fixed polarization,
detecting the average intensity of said intensity modulated beam,
detecting the amplitude of said intensity modulated beam at the frequency of modulation thereof, and
comparing said detected average intensity with said detected amplitude, the magnitudes of said average intensity and said amplitude being indicative of the sum and difference, respectively, of the intensities of said two linearly polarized components of the daylight and, accordingly, a measure of visibility, the closer the magnitudes to none another of said average intensity and said amplitude, the better the visibility and the longer the range.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for measuring visibility from the polarization properties of the daylight sky

Life of this patent

Method and apparatus for measuring visibility from the polarization properties of the daylight sky

Life of this patent

Abstract

Claims22