The Brewer instrument

Brewer operates automatically and is designed to measure total ozone and sulphur dioxide in the atmosphere. In addition, the instrument measures direct and global (direct + diffuse) spectral irradiance in the wavelength range 290 - 372 nm. During sunny days total ozone is derived from direct sun (DS) measurements at 4 UV wavelengths. For cloudy sky conditions ozone can be derived from scattered UV radiation from the zenith direction. The present algorithms for deriving total ozone from zenith measurements are sensitive to clouds. Therefore we use a modified DS routine to redirect the 5 Brewer standard wavelengths through the UV-B irradiance port and use a similar technique as with the GUV-511. This technique has shown to be little sensitive to clouds. Consequently, our Brewer provides high quality toatal ozone measurements the year around. The Brewer instrument in Oslo has been in operation since 1990.

More Brewer pictures: View from the roof

The Dobson spectrophotometer

The Dobson instrument was developed by G.M.B. Dobson in the 1920s. It is designed to measure total ozone abundance in the atmosphere. The instrument is operated manually and the ozone abundance is deduced from direct sun measurements or zenith sky measurements. The Dobson spectrophotometer is known to be a very stable instrument and constitutes the basis of the global ozone monitoring network. From 1978 to 1998 total ozone was measured at the University of Oslo with Dobson #56.

The GUV-511 instrument

This is a 5 channel instrument designed to measure UV irradiances at 4 channels, with center wavelengths at 305 nm, 320 nm, 340 nm and 380 nm. Bandwidths are approximately 10 nm FWHM (Full Width at Half Maximum). The fifth channel is a PAR channel (Photosynthetically Active Radiation, 400-700 nm). The instrument is manufactured by Biospherical Instruments Inc, USA. The instrument is temperature stabilized at 40ºC and has a time resolution of 1 min. Using a technique developed by Dahlback (1996), we are able to derive total ozone abundance, cloud cover information, complete UV spectra from 290 to 400 nm and biologically weighted UV doses for any action spectra in the UV. The irradiance measurements may also be used to derive spectral actinic fluxes to compute photodissociation rates for different photochemical processes (Beine et al, 1999).