An acoustic method for determination of the effective temperature and refractive index of air

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    Abstract

    An acoustic method for measurement of the effective temperature and refractive index of air along a laser beam path is described. The method can be used to improve the accuracy of interferometric length measurements outside the best laboratories, and even in severe environmental conditions. The method is based on the measurement of the speed of ultrasound over the same distance measured with a laser interferometer. The effectiveness of the method derives from the fact that the relative effect of a change in air temperature is about two thousand times greater on the speed of sound than on the refractive index of air. Experimental equations for the effective temperature or refractive index of air as a function of the speed of sound, pressure, humidity and CO 2 concentration are fitted using the measured speed of sound, the Cramer equation, the dispersion correction and Edlén equations. The standard uncertainties of the effective temperature and the refractive index of air equations are estimated to be 15 mK and 1.7×10-8, respectively. The uncertainties of the effective temperature and refractive index of air measured with the. test setup were 25 mK and 2.6×10 -8 (for L = -5 m), respectively.

    Original languageEnglish
    Title of host publicationRecent Developments in Traceable Dimensional Measurements II
    PublisherInternational Society for Optics and Photonics SPIE
    Pages316-326
    DOIs
    Publication statusPublished - 1 Dec 2003
    MoE publication typeA4 Article in a conference publication
    EventRecent Developments in Traceable Dimensional Measurements II - San Diego, CA, United States
    Duration: 4 Aug 20036 Aug 2003

    Publication series

    SeriesProceedings of SPIE
    Volume5190
    ISSN0277-786X

    Conference

    ConferenceRecent Developments in Traceable Dimensional Measurements II
    CountryUnited States
    CitySan Diego, CA
    Period4/08/036/08/03

    Keywords

    • Effective temperature of air
    • Length interferometry
    • Refractive index of air
    • Speed of ultrasound in air

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