On Mars the UV climate is quite different than on Earth, because the thin atmosphere of Mars, mainly carbon dioxide, is not able to absorb the short wavelengths of UV radiation as the terrestrian atmosphere does. Therefore energy-rich UV radiation (wavelengths down to 200 nm) can reach the surface of Mars. The exact measurements of the biological effectiveness of that UV radiation on biological processes in terrestrial organisms is of importance for the future development of bioregenerative life support systems and agricultural plants for Mars.

The assessment of the influence of environmental UV radiation on critical biological processes requires monitoring systems that weight the spectral irradiance according to the biological responses under consideration. The need for a biological weighting of solar UV irradiance derives from the highly wavelength-dependent sensitivity, expressed as the so-called action spectrum, of biological systems in the UV range of the electromagnetic spectrum. Biological UV dosimeters, that weight directly the incident UV components of sunlight in relation to the effectiveness of the different wavelengths and the interactions between them, can complement weighted physical UV measurements.

Here at the MDRS we are using a well-characterized biological UV dosimeter, the DLR-Biofilm. It consists of spores of the ubiquitous apathogenic bacterium B. subtilis as UV sensor. We are performing different biological UV dosimetry experiments:

1. Personal UV dosimetry of crew members during EVAs compared to parallel stationary biological measurements of ambient UV radiation, to get informations about the influence of movements and the type of activities on the individual UV doses. These measurements are performed during each EVA.
   
   
2. Measurement of the biological efffective UV doses beneath layers of natural soil of different thickness compared to parallel samples with the Martian soil analogue JSC Mars-1 to get informations about the shielding capacity of soil and dust, e.g. on Mars. We already have finished one short exposure (2 days) and started one long exposure (9 days).
   
   
3. Measurement of diurnal UV profiles with larger DLR-Biofilms than those used for personal UV dosimetry that have 20 measurement areas on each film to see changes in the solar irradiance during the day. This will be done in the next week.
   
   
4. In addition the erythemaly weighted UV radiation is measured with an electronic UV dosimeter (X20001, Gigahertz-Optik, Germany) for a direct comparison with the biological UV data. The time-resolved data are downloaded every evening.