Why Umkehr

The Arosa Umkehr series started 1956. No other series provides such a long record of the undisturbed ozone in the upper stratosphere. Umkehr covers a range up to 40 km which is not reached by operational balloon soundings.
 

The Umkehr profile is normally given in 10 layers, named L1 to L10, although the resolution is worse. It fits reasonably with other ozone profiling methods. For trend analysis it is strongly recommended to combine L1, L2 and L3 in a layer L3-, and to add L8, L9, L10 as a layer L8 +.

The Umkehr method is ground based optical remote sensing. The intensity relations of two wavelengths is compared, one of which is strongly, the other one weakly absorbed by ozone.  From the  logarithmic intensity relation and instrumental and extra- terrestrial constants, the N-values are calculated. Plotted over the solar angle, this is called an Umkehr curve. The Umkehr algorithm employs the inversion technique of Rodgers (1976), to estimate  an ozone  profile from this Umkehr curves and from the separately measured total ozone. Umkehr suffers from all the deficiencies inherent to remote sensing and inversion techniques.

Several Umkehr instruments run at the LKO (Lichtklimatisches Observatorium) at Arosa. They belong to the Swiss Met office and are carefully maintained. Here the Dobson spectrophotometer D101 is depicted.

New! Recent analysis of instrument stability published here: statement (after  April 2000)

Rodgers, C. D. Retrieval of Atmospheric Temperature and Composition from Remote Measurements or Thermal Radiation. Reviews of Geophysics and Space Physics, Vol 14, 609-624, 1976.

Mateer, C. L. and  DeLuisi, J. J. A new Umkehr inversion algorithm. J. Atmospheric and Terrestrial Physics,
Vol 54, 537-556, 1992.

Mateer, C. L. and Duetsch, H.U. and Staehelin, J and DeLuisi, J. J. Influence of a priori profiles on trend calculations from Umkehr data. J. Geophysical Research,  Vol 101, 16,779-16,787, 1996.