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Sun Radiometry and
Transmittance



Background

Natural sun radiation is linked to humans life. Absolute spectroradiometric measurements of natural sun radiation is required by industries in the following areas: energy, cosmetics, materials, pharmaceutical, medicine, textiles, and laundry, among others.

New developments in the photonics industry are helping to obtain accurate and affordable absolute measurements in the range of 250nm to 850nm, full traceable to international standards, as well as new hardware and software capabilities are helping to process large numeric data using cheap and simple procedures. Currently, absolute measurements of UVB, UVA-II, UVA-I and Visible natural radiation, at different planes at ground level, are now part of daily measurements in several industries.



Examples:

1. Global solar spectral irradiance

Based on spaceborne irradiance measurement, the solar constant value of 1366 W/m2 was recently confirmed as well as the solar extraterrestrial spectrum in the range of 0nm to 4 um at top of the atmosphere (1). From that spectra, others at terrestrial level are usually predicted through the use of radiative transfer models. On the other hand actual absolute measurements at ground level are currently obtained to validate theoretical models.

From the top of the atmosphere to ground level, the solar spectrum change is due to geometrical and geophysical variables (2):

  • Geometrical variables are the distance between Earth and Sun and the solar zenith angle of the sun at a specific time and location on the Earth's surface
  • Geophysical variables include atmospheric constituents that absorb or scatter radiation as it passes through the atmosphere or scatter radiation at the Earth's surface. The absorbing variables include ozone, nitrogen oxide, sulphur oxide, and absorbing aerosols. The scattering variables include clouds, non-absorbing aerosols, and snow or ice at the Earth's surface.


Y = uW/(cm2*nm)
SUN, current accepted extraterrestrial spectral irradiance (1)
FIN_MAX_Q, spectral irradiance taken at ground level in Quito, on equinox 09/2006, one the highest collected at populated environment.

***


Y = uW/(cm2*nm)
SUN, current accepted extraterrestrial spectral irradiance (1)
FIN_MAX_Q, spectral irradiance taken at ground level in Quito, on equinox 09/2006
ALBUQUERQUE, spectral irradiance taken at Albuquerque, NM USA, July 3 1990, Noonday (3).

2. Photobiological weighted spectrum


Y = uW/(cm2*nm)
SPECINIABS, current accepted extraterrestrial spectral irradiance (1)
MAX_SUN, spectral irradiance taken at ground level in Quito, on equinox 09/2006
CIE.ACTIUMSPECTRA, CIE accepted erythema action spectrum(4).

3. Transmittance test


NAT.UV, natural ultraviolet spectral irradiance, reference spectrum
S1, S2, S3, S4, spectral irradiance of energy transmitted by films with commercial sunscreens (5).



References

(1) Gueymard, C.A., The sun's total and spectral irradiance for solar energy applications and solar radiation models, Solar Energy, 76 (2004) 423-453. Solar Consulting Services, USA.
(2) Kerr, J.B., Understanding the Factors that Affect Surface UV radiation, Proceedings of SPIE Vol 5156 (2003) Ultraviolet Ground- and Space-based Measurements, Models, and Effects III, 1-14. Meteorological Service of Canada, CANADA.
(3) Sayre, R.M., et al., Spectral Comparison of Solar Simulators and Sunlight, Photodermatol Photoimmunol Photomed., 7, 159-165 (1990). University of Tennesse, USA.
(4) CIE 151:2003, Spectral Weighting of Solar Ultraviolet Radiation, CIE, 2003. AUSTRIA
(5) AS/NZS 2604:1998, Sunscreen products-Evaluation and classification. Australian/New Zealand Standard


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