Highly accurate in-situ determination of the refractivity of an ambient atmosphere

US5218426A · kind A · utility

Assignee

• Government of the United States of America, as represented by the Secretary of Commerce · US

Inventors

• John L. Hall · Tracy, US
• Peter Martin · Richmond, US
• Mark L. Eickhoff · Boulder, US
• Michael P. Winters · Pasadena, US

Key dates

• Filing date: Jul 1, 1991
• Grant date: Jun 8, 1993
• Expiry date: Jul 1, 2011

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N2021/4106
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A highly accurate in-situ determination of the refractivity of an ambient atmosphere is disclosed, which determination is utilizable to enhance the accuracy of a quantity measurement. The system includes use of a refractometer exposed to an ambient atmosphere and having light directed thereto to form an optical interference fringe pattern having a dependence upon the refractivity of the ambient atmosphere. The fringe pattern is measured as a function of angle either by sequentially scanning a collimated input beam in angle while collecting and detecting the transmitted light, or by imaging (onto a multi-element detector) the angular exit space of the interferometer illuminated with a diverging input beam. The electrical output of the detector is processed to provide an output indicative of the index of refraction of the ambient atmosphere. The determined index of refraction is utilizable to enhance the accuracy of a quantity measurement, such as, for example, the distance measurement provided by a Fabry-Perot or displacement-measuring Michelson interferometer.