Spectroscopic measurement of air temperature

T. Hieta, M. Merimaa

Research output: Contribution to journalArticleScientificpeer-review

10 Citations (Scopus)

Abstract

Optical dimensional measurements have to be corrected for the refractive index of air. The refractive index is conventionally calculated from parameters of ambient air using either Edlén or Ciddor equations or their modified versions. However, these equations require an accurate knowledge of ambient conditions and especially the temperature of air. For example, to reach an uncertainty of 10−7 in dimensions, the air temperature has to be known at ~100 mK level. This does not necessarily cause problems in a stable laboratory environment. However, if measurements are done outdoors or in an industrial environment, variations in temperature can be very rapid and local temperature gradients can cause significant error if not taken into account. Moreover, if the required distance is long, the temperature over the whole measurement path can be impractical or impossible to determine at sufficient temporal or spatial resolution by conventional temperature measurement techniques. The developed method based on molecular spectroscopy of oxygen allows both lateral spatial and temporal overlap of the temperature measurement with the actual distance measurement. Temperature measurement using spectroscopy is based on a line intensity ratio measurement of two oxygen absorption lines, previously applied for measurements of high temperatures in flames. The oxygen absorption band at 762 nm is a convenient choice for two-line thermometry since the line strengths are practical for short- and long-distance measurements and suitable distributed feedback lasers are commercially available. Measurements done on a 67 m path at ambient conditions demonstrate that the RMS noise of 22mK, or 7.5 × 10−5, near 293 K using 60 s measurement time can be achieved, which is to our knowledge the best reported resolution.
Original languageEnglish
Pages (from-to)1710-1718
Number of pages9
JournalInternational Journal of Thermophysics
Volume31
Issue number8-9
DOIs
Publication statusPublished - 2010
MoE publication typeA1 Journal article-refereed

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air
temperature measurement
temperature
oxygen
refractivity
molecular spectroscopy
dimensional measurement
causes
distributed feedback lasers
temporal resolution
flames
temperature gradients
spatial resolution
time measurement
absorption spectra
spectroscopy

Cite this

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title = "Spectroscopic measurement of air temperature",
abstract = "Optical dimensional measurements have to be corrected for the refractive index of air. The refractive index is conventionally calculated from parameters of ambient air using either Edl{\'e}n or Ciddor equations or their modified versions. However, these equations require an accurate knowledge of ambient conditions and especially the temperature of air. For example, to reach an uncertainty of 10−7 in dimensions, the air temperature has to be known at ~100 mK level. This does not necessarily cause problems in a stable laboratory environment. However, if measurements are done outdoors or in an industrial environment, variations in temperature can be very rapid and local temperature gradients can cause significant error if not taken into account. Moreover, if the required distance is long, the temperature over the whole measurement path can be impractical or impossible to determine at sufficient temporal or spatial resolution by conventional temperature measurement techniques. The developed method based on molecular spectroscopy of oxygen allows both lateral spatial and temporal overlap of the temperature measurement with the actual distance measurement. Temperature measurement using spectroscopy is based on a line intensity ratio measurement of two oxygen absorption lines, previously applied for measurements of high temperatures in flames. The oxygen absorption band at 762 nm is a convenient choice for two-line thermometry since the line strengths are practical for short- and long-distance measurements and suitable distributed feedback lasers are commercially available. Measurements done on a 67 m path at ambient conditions demonstrate that the RMS noise of 22mK, or 7.5 × 10−5, near 293 K using 60 s measurement time can be achieved, which is to our knowledge the best reported resolution.",
author = "T. Hieta and M. Merimaa",
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language = "English",
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Spectroscopic measurement of air temperature. / Hieta, T.; Merimaa, M.

In: International Journal of Thermophysics, Vol. 31, No. 8-9, 2010, p. 1710-1718.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Spectroscopic measurement of air temperature

AU - Hieta, T.

AU - Merimaa, M.

PY - 2010

Y1 - 2010

N2 - Optical dimensional measurements have to be corrected for the refractive index of air. The refractive index is conventionally calculated from parameters of ambient air using either Edlén or Ciddor equations or their modified versions. However, these equations require an accurate knowledge of ambient conditions and especially the temperature of air. For example, to reach an uncertainty of 10−7 in dimensions, the air temperature has to be known at ~100 mK level. This does not necessarily cause problems in a stable laboratory environment. However, if measurements are done outdoors or in an industrial environment, variations in temperature can be very rapid and local temperature gradients can cause significant error if not taken into account. Moreover, if the required distance is long, the temperature over the whole measurement path can be impractical or impossible to determine at sufficient temporal or spatial resolution by conventional temperature measurement techniques. The developed method based on molecular spectroscopy of oxygen allows both lateral spatial and temporal overlap of the temperature measurement with the actual distance measurement. Temperature measurement using spectroscopy is based on a line intensity ratio measurement of two oxygen absorption lines, previously applied for measurements of high temperatures in flames. The oxygen absorption band at 762 nm is a convenient choice for two-line thermometry since the line strengths are practical for short- and long-distance measurements and suitable distributed feedback lasers are commercially available. Measurements done on a 67 m path at ambient conditions demonstrate that the RMS noise of 22mK, or 7.5 × 10−5, near 293 K using 60 s measurement time can be achieved, which is to our knowledge the best reported resolution.

AB - Optical dimensional measurements have to be corrected for the refractive index of air. The refractive index is conventionally calculated from parameters of ambient air using either Edlén or Ciddor equations or their modified versions. However, these equations require an accurate knowledge of ambient conditions and especially the temperature of air. For example, to reach an uncertainty of 10−7 in dimensions, the air temperature has to be known at ~100 mK level. This does not necessarily cause problems in a stable laboratory environment. However, if measurements are done outdoors or in an industrial environment, variations in temperature can be very rapid and local temperature gradients can cause significant error if not taken into account. Moreover, if the required distance is long, the temperature over the whole measurement path can be impractical or impossible to determine at sufficient temporal or spatial resolution by conventional temperature measurement techniques. The developed method based on molecular spectroscopy of oxygen allows both lateral spatial and temporal overlap of the temperature measurement with the actual distance measurement. Temperature measurement using spectroscopy is based on a line intensity ratio measurement of two oxygen absorption lines, previously applied for measurements of high temperatures in flames. The oxygen absorption band at 762 nm is a convenient choice for two-line thermometry since the line strengths are practical for short- and long-distance measurements and suitable distributed feedback lasers are commercially available. Measurements done on a 67 m path at ambient conditions demonstrate that the RMS noise of 22mK, or 7.5 × 10−5, near 293 K using 60 s measurement time can be achieved, which is to our knowledge the best reported resolution.

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