Solar UVB measurements with the double- 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 obtained by a conventional, single-monochromator Brewer instrument. The comparison shows that the performance of the new instrument is much superior in the low UVB wavelengths (lambda<305 nm), because of the much higher stray-light rejection capability of the instrument. The conventional Brewer spectrophotometer is capable of recording accurately solar UVB spectra at wavelengths greater than about 300 nm. The error in UVB dose calculations made using data from the conventional Brewer is estimated to be of the order of +1%, while the absolute irradiances at wavelengths below 300 nm may be overestimated by more than 10%, depending on the measured wavelength and the solar zenith angle.