Vol. 15, issue 04, article # 15

Abstract:

The contribution from direct and scattered ultraviolet radiation (295-345 nm) is estimated based on measurements with a spectrophotometer having a fixed entrance aperture (central angle of 32°). It is shown that in a certain range of the sun elevation angles and in some wavelength region, it is possible to separate out direct ultraviolet radiation (UVR) component from recorded signals. The procedure of separating the direct UVR is applied to processing and analyzing the daily near-noon values of UVR recorded in Irkutsk in 1998-2000. The experimental data on the annual UVR variation amplitude in Irkutsk (the sun elevation angle from 14 to 60°) are compared with calculated values of annual variation amplitudes of direct and scattered UVR. It is concluded that the observed variations in the recorded UVR correlate to a greater extent with variations of direct radiation. The proposed method of separating the direct UVR is intended for monitoring and investigation of long-term (such as interseasonal and interannual) UVR variations.