### 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 language | English |
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Title of host publication | Recent Developments in Traceable Dimensional Measurements II |

Publisher | International Society for Optics and Photonics SPIE |

Pages | 316-326 |

DOIs | |

Publication status | Published - 1 Dec 2003 |

MoE publication type | A4 Article in a conference publication |

Event | Recent Developments in Traceable Dimensional Measurements II - San Diego, CA, United States Duration: 4 Aug 2003 → 6 Aug 2003 |

### Publication series

Series | Proceedings of SPIE |
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Volume | 5190 |

ISSN | 0277-786X |

### Conference

Conference | Recent Developments in Traceable Dimensional Measurements II |
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Country | United States |

City | San Diego, CA |

Period | 4/08/03 → 6/08/03 |

### Fingerprint

### Keywords

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

### Cite this

*Recent Developments in Traceable Dimensional Measurements II*(pp. 316-326). International Society for Optics and Photonics SPIE. Proceedings of SPIE, Vol.. 5190 https://doi.org/10.1117/12.504468

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*Recent Developments in Traceable Dimensional Measurements II.*International Society for Optics and Photonics SPIE, Proceedings of SPIE, vol. 5190, pp. 316-326, Recent Developments in Traceable Dimensional Measurements II, San Diego, CA, United States, 4/08/03. https://doi.org/10.1117/12.504468

**An acoustic method for determination of the effective temperature and refractive index of air.** / Lassila, Antti; Korpelainen, Virpi.

Research output: Chapter in Book/Report/Conference proceeding › Conference article in proceedings › Scientific › peer-review

TY - GEN

T1 - An acoustic method for determination of the effective temperature and refractive index of air

AU - Lassila, Antti

AU - Korpelainen, Virpi

PY - 2003/12/1

Y1 - 2003/12/1

N2 - 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.

AB - 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.

KW - Effective temperature of air

KW - Length interferometry

KW - Refractive index of air

KW - Speed of ultrasound in air

UR - http://www.scopus.com/inward/record.url?scp=2342582162&partnerID=8YFLogxK

U2 - 10.1117/12.504468

DO - 10.1117/12.504468

M3 - Conference article in proceedings

AN - SCOPUS:2342582162

T3 - Proceedings of SPIE

SP - 316

EP - 326

BT - Recent Developments in Traceable Dimensional Measurements II

PB - International Society for Optics and Photonics SPIE

ER -