Surface UV radiation monitoring based on GOME and SCIAMACHY -- UV radiation and action spectra

Surface UV radiation monitoring based on GOME and SCIAMACHY

Jos van Geffen, Ronald van der A, Michiel van Weele, Marc Allaart and Henk Eskes
in: Proceedings of the ENVISAT & ERS Symposium, 6-10 September 2004,
Salzburg, Austria, ESA publication SP-572, 2005 (CD-ROM).

2. UV radiation and action spectra

Ultraviolet light is usually divided into three components: UV-A (320-400 nm), UV-B (280-320 nm) and UV-C (200-280 nm). The UV-C component of the Solar UV light is potentially the most dangerous as it has the highest energy levels, but this component is completely absorbed by ozone and oxygen above about 30 km. The UV-B component is strongly absorbed by ozone, but a small fraction reaches the Earth's surface. The UV-A is only weakly absorbed by ozone, with some scattering of radiation near the surface.

Most of the UV radiation reaching the surface is therefore UV-A. Due to the higher energy levels of UV-B, however, the UV-B component has more effect on flora and fauna than UV-A. An action spectrum is a parameter function which describes the relative effect of energy at different wavelengths in producing a certain biological response. These effects may be at a molecular level, such as DNA damage, or at the level of the whole organism, such as plant growth. An action spectrum is used as a "weighting function" for the UV spectrum in an integration of the monochromatic UV irradiance.

Figure 1. Action spectra of the susceptibility of the human skin to erythema (sunburn) and of generalised DNA damage due to UV radiation. The erythemal UV index is an integration between 280 and 400 nm of the UV irradiance at ground level, weighted with the erythemal action spectrum. The DNA-damage UV index is an integration between 256 and 370 nm of the UV irradiance at ground level, weighted with the DNA-damage action spectrum.

For the TEMIS data service the two action spectra illustrated in Fig. 1 are used:

The CIE action spectrum for erythema (reddening of the skin due to sunburn), proposed by McKinlay & Diffey [5] and adopted as a standard by the Commission Internationale de l'Éclairage (International Commission on Illumination).
An action spectrum for generalised DNA-damage, which has been determined by Setlow [6] and was parametrised by Bernard and Seckmeyer [7].

These action spectra stress the importance of the UV-B component. Of the global UV irradiance at the surface, 94% is UV-A and 6% is UV-B. Whereas of the erythemal UV irradiance at the surface, for example, 17% is UV-A and 83% is UV-B.

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Surface UV radiation monitoring based on GOME and SCIAMACHY

2. UV radiation and action spectra

created: 3 September 2004 last modified: 19 August 2020

created: 3 September 2004
last modified: 19 August 2020