抄録
It is very important to know characteristics of the variation of ultraviolet radiations (UVR) in the natural environment for planning radiation protection on the basis of quantitative risks of the UVR. From this point of view, observation of diurnal and annual variations in the natural environment has been carried out using a portable UVR irradiance meter from May 1991 to April 1992. It is quite possible from the diurnal variation that the UVB scattered in the sky become significant when the sun approaches the horizon and from the annual variation that UVB irradiances become weaker than expected ones in summer. It is apparent that the UVA scattered in the sky vary depending on the surroundings of measuring points and that remarkable seasonal variations can be seen in the UVB scattered in the sky.
