BIOLOGICAL DOSIMETRY OF SOLAR-RADIATION FOR DIFFERENT SIMULATED OZONECOLUMN THICKNESSES

During the Spacelab mission D-2, in the experiment RD-UVRAD, precalibr ated biofilms consisting of dry monolayers of immobilised spores of Ba cillus subtilis (strain Marburg) were exposed, for defined intervals, to extraterrestrial solar radiation filtered through an optical filter ing system, to simulate different ozone column thicknesses. After the mission, the biofilms were processed and optical densities indicative of any biological activity were determined for each exposure condition by image analysis. For the different simulated ozone column thickness es, biologically effective irradiances were experimentally determined from the biofilm data and compared with calculated data using a radiat ive transfer model and the known biofilm action spectrum. The data sho w a strong increase in biologically effective solar UV irradiance with decreasing (simulated) ozone concentrations. The full spectrum of ext raterrestrial solar radiation leads to an increment of the biologicall y effective irradiance by nearly three orders of magnitude compared wi th the solar spectrum at the surface of the Earth for average total oz one columns.