Effect of the out-of-band stray light on the retrieval of the Umkehr Dobson ozone profiles

Abstract

The technique of producing a vertical ozone profile using ground-based observations of the Umkehr effect is well established and is widely used for ozone trend analysis. Still, observations of the Umkehr effect by Dobson ozone spectrophotometers have a documented problem: simultaneous measurements from collocated instruments produce noticeably different results, with the difference shown to be dependent on solar zenith angle and total ozone. Ozone profiles are thus difficult to compare from station to station. Current investigations into the level and effects of stray light within the instrument suggest that much of the difference can be attributed to out-of-band stray light characteristics of individual Dobson instruments. Resulting changes in retrieved ozone profiles suggest that adjusting measurements for stray light components removes much of the existing bias between Umkehr profiles and other ozone measuring datasets. This new information has implications for both observational methods and completeness of the existing datasets.