Measured and Theoretical Values of the Spectral Intensity of Ultraviolet Zenith Radiation and Direct Solar Radiation at 316, 1580 and 2818 m a.s.l.

Measurements of zenith intensity of the clear sky and of direct solar intensity have been taken for selected wavelengths between lambda297.5 and 400 nm at Biel, Davos and Weissfluhgipfel. A spectrophotometer described has been used. The ratio between the intensity of sky brightness and direct solar radiation is examined. The measured data, partly interpolated for round values of solar altitude, and the mean values averaged over all results obtained for a given elevation are presented in tables and discussed. The apparent values of extraterrestrial solar intensity and of optical thickness for extinction and aerosal scattering are tabled and analyzed. Theoretical values of intensity for a Rayleigh atmosphere have been included into the tables to facilitate a comparison with measured data. A satisfactory agreement with theory is obtained, if measured and theoretical values of zenith intensity for lambda or 330 nm are examined in dependence on the measured values of optical thickness of extinction including Rayleigh-and aerosal scattering for the days in question. Author