Ozone profiles by the Umkehr method at Arosa

Actually, 4 spectrophotometers measure ozone profiles at Arosa. The Umkehr ozone profile serie started in 1956 with the Dobson 15. The spectrophotometer Dobson 51 is fully automated and gives 2 ozone profiles per day since 1980. The spectrophotometers Dobson 101 and 62 allow manual redundance with 4-6 profiles per month since 1967 resp. 1992. The spectrophotometer Brewer 40, also fully automated, produces 2 ozone profiles per day since 1988.

Umkehr method

Direct solar intensity is measured at 2 different wavelengths, one being more absorbed by ozone than the other. At sunrise and sunset, the intensities decrease at different rates. The ratio shows an inversion. This is called the Umkehreffekt and gives information about the vertical distribution of ozone in the atmosphere.

The vertical ozone distribution can be obtained by numerical inversion from the log of the intensity ratio using successive approximations from an a priori ozone profile (optimal estimation method, Rodgers).

Zenith sky light (UV) is measured at 2 wavelengths (Dobson) and their intensity is plotted vs. solar zenith angle (Umkehr curve). From this curve an inversion algorithm calculates the Umkehr profiles

Zenith sky measurement of the intensity ratio of 2 wavelengths vs solar zenith angle, N values vs solar zenith angle and ozone profile after inversion by the optimal estimation method.

Ozone profiles by the Umkehr method

Dobson 51 ozone isopleths for the year 2009 in Dobson units. Ozone quantities higher than 75 DU are measured from January to April.

Dobson 51 ozone isopleths for the year 2009 in Dobson units. Ozone quantities over 75 DU are measured from January to April wich is a longer period than in 2008.