@prefix skos: . skos:prefLabel "Profilers/Sounders"@en ; a skos:Concept ; skos:narrower . skos:definition """Umkehr observations of the vertical profile of ozone up to 50 km, beginning in the late 1950s, were the only source of data for trend analysis of ozone changes in the photochemical region near 40 km until satellite data became available starting in 1979. The Umkehr ozone profile trend analysis performed in the early 1980s on the historical data set indicated a significant reduction in ozone concentration near 40 km. Confirmation of ground-based and satellite trend results, published in 1992, has greatly improved the credibility of the data derived from both methods of observations. While the Umkehr observation produces laudable results, the method is sensitive to stratospheric aerosol interference (especially during elevated aerosol loading conditions after a significant volcanic eruption) and this requires information on the profiles and optical properties of the stratospheric aerosol to account for the interference. The method to correct Umkehrs for stratospheric aerosol is tedious and complex and has not been fully developed up to the level that it should be. The research funded by the Department of Energy will provide a comprehensive data set on stratospheric aerosols back to 1958, will evaluate the uncertainties in the method of correction, and will provide a measure of the uncertainties in the application of Umkehr data for trend analysis. Additional information available at "http://www.atmos.anl.gov/ACP/5-ozone_summtab.html" [Summary provided by University of Colorado and NOAA]"""@en ; skos:prefLabel "UMKEHR OBSERVATIONS"@en ; skos:inScheme ; skos:broader ; a skos:Concept .