Spectral irradiance and radiation temperature scales

Maija Ojanen

Research output: ThesisDoctoral ThesisCollection of Articles


Spectral irradiance and radiation temperature measurements are needed in various applications, from environmental studies to different fields of industry. Scale realizations are needed to serve the calibration needs of these applications. In this thesis, I present various improvements to the scales of spectral irradiance and radiation temperature. A physical model was developed for tungsten halogen lamps utilized as spectral irradiance sources. The model consists of Planck's radiation law, emissivity of tungsten in polynomial form, and a correction function. The model can interpolate the spectral irradiance values of lamps with an agreement better than 1 % with previous calibrations by MIKES/TKK and NPL (UK) throughout the spectral region 340 nm - 850 nm. Spectral irradiance scales of MIKES/TKK and NMC (Singapore) were compared using an automated multi-wavelength filter radiometer. The wavelength range of the comparison was 290 nm - 900 nm. The agreement was compared with the results of the previous key comparison. The results indicated that the long-term reproducibility of the spectral irradiance scale of MIKES is excellent in the wavelength range above 400 nm. In the range 290 nm - 400 nm, the reproducibility is within 2.8 %, which is still within the expanded uncertainties of the comparison. The spectral irradiance scale of NIMT (Thailand) was linked to the CIPM key comparison reference value using MIKES as a link in a bilateral key comparison. I present a method for uncertainty estimation in linking key comparisons. A detector-based radiation temperature scale was developed at MIKES. Filter radiometers were first compared with a Ag fixed point cell, and then with a linear pyrometer in the temperature range of 1370 K - 1770 K. With help of the filter radiometers, the extrapolation of the pyrometer readings could be studied. The radiation temperature scales of MIKES and PTB (Germany) were compared in the range 1570 K - 2770 K. Both the International Temperature Scale of 1990 (ITS-90) and thermodynamic temperature scales were compared. The ITS-90 based scales were in agreement. The agreement of the thermodynamic temperature scales was partial: The results for two out of four filter radiometers of MIKES agreed with each other and with those of PTB, whereas the results from the two others showed deviations. Possible reasons for this deviation, such as differences in measurement geometries and possible diffuse transmittance in the interference filters, are postulated and discussed.
Translated title of the contributionSpectral irradiance and radiation temperature scales
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Kärhä, Petri, Thesis Advisor
  • Ikonen, Erkki, Thesis Advisor
Print ISBNs978-952-60-3155-2
Electronic ISBNs978-952-60-3156-9
Publication statusPublished - 2010
MoE publication typeG5 Doctoral dissertation (article)


  • filter radiometer
  • key comparison
  • radiation temperature
  • spectral irradiance
  • tungsten halogen lamp

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