Spectroscopic thermometry for long-distance surveying

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2 Citations (Scopus)


Electronic distance meters are routinely used to accurately determine the distance between two points. To reach relative measurement uncertainties of 10-7, the average temperature along the beam has to be known within 100 mK since it is a key component in determining the refractive index of air. Temperature measurements at this level are extremely challenging over long distances and especially in an outdoor environment. This paper presents a thermometer for accurate temperature measurements over distances up to a few km. The thermometer is based on direct laser absorption spectroscopy of oxygen near 770 nm. The thermometer yields a spatially continuous measurement of air temperature, and it can provide spatially and temporally well-matching data with an actual distance-measuring laser beam. A field measurement campaign at the 864-m Nummela standard baseline demonstrates applicability of the developed thermometer for improving the refractive index compensation of current high-performance electronic distance meters.
Original languageEnglish
Pages (from-to)239-246
Number of pages8
JournalApplied Optics
Issue number2
Publication statusPublished - 10 Jan 2017
MoE publication typeA1 Journal article-refereed


  • absorption spectroscopy
  • laser beams
  • refractive index
  • temperature measurement
  • thermometers
  • air temperature
  • continuous measurements
  • electronic distance meters
  • field measurement
  • laser absorption spectroscopy
  • outdoor environment
  • refractive index of air
  • relative measurement

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