Effect of temperature on biological dose rates derived from spectral solar UV irradiance measurements.  

• Trond Morten Thorseth*, Berit Kjeldstad  and Christer Jensen

  Norwegian University of Science and Technology, Department of Physics, N-7034 Trondheim, Norway.
  * To whom correspondence should be addressed. (email: Trond.Thorseth@phys.ntnu.no)

• ABSTRACT

  Accurate spectral solar irradiance measurements depend upon a good calibration. If the spectroradiometer operates at a different temperature than the calibration temperature, sensitivity and wavelength setting of the instrument will change. This is the case for most spectroradiometers, but the magnitude of this effect will vary for different types of instruments. In this study a widely used spectroradiometer, Optronic OL752,  from Optronic Laboratories Inc. has been investigated. Both the effect of temperature on sensitivity and wavelength shift has been quantified. The sensitivity of the Optronic OL752 in the ultraviolet region, 290-400 nm, decreased approximately 0.8 %/K when the instrument was heated above the calibration temperature. Wavelength shift coefficients were derived for several wavelength regions with two independent methods. One of the methods used was direct observation of how the measured spectral lines from a Hg lamp, shifted with temperature. The other method, calculated the relative shift in the spectral global irradiance measurements by comparing the Fraunhofer structure in the measured spectra to the structure in an extraterrestrial spectrum. OL752 had a systematic wavelength shift, varying from 0.10 nm/K  at 254 nm  to 0.06 nm/K at 633 nm. CIE-weighted irradiance derived from modeled data, was used to estimate errors due to temperature effects. If the spectroradiometer temperature is not controlled, a change of 5 K may lead to an error in the derived CIE-weighted irradiance from 10% to 15% dependent upon solar zenith angle and atmospheric conditions.