SOLAR UVB MEASUREMENTS WITH THE DOUBLE-MONOCHROMATOR AND SINGLE-MONOCHROMATOR BREWER OZONE SPECTROPHOTOMETERS

In this work, the new double-monochromator version of the Brewer Ozone Spectrophotometer, especially designed for spectral UV measurements, is briefly described and its measurements are compared with those obta ined by a conventional, single-monochromator Brewer instrument. The co mparison shows that the performance of the new instrument is much supe rior in the low UVB wavelengths (lambda<305 nm), because of the much h igher stray-light rejection capability of the instrument. The conventi onal Brewer spectrophotometer is capable of recording accurately solar UVB spectra at wavelengths greater than about 300 nm. The error in UV B dose calculations made using data from the conventional Brewer is es timated to be of the order of +1%, while the absolute irradiances at w avelengths below 300 nm may be overestimated by more than 10%, dependi ng on the measured wavelength and the solar zenith angle.