Blocking improved narrow-band filters for the UV-B region

Monitoring stratospheric ozone depletion with filter radiometers requires narrow-band filters with outstanding parameters. First, depending on customer specifications, the filter's central wavelength must meet an extremely precise value between 290 and 320 nm. Second, this central wavelength must be unusually stable over long periods of time and under changing environmental conditions due to the very small shifts that must be detected in the steep cutoff of the solar irradiance spectra. Third, the filter passband must have a very narrow bandwidth with steep cutoffs. Last, but not least, a strong attenuation of light for longer wavelengths is essential while retaining high transmittance at the central wavelength. Data of improved UV-B narrow-band filters and a detailed description of attenuation of longer wavelengths in solar UV-B radiometers are presented.