The National Institute for Public Health and the Environment (RIVM) hasexamined the quality of SCIAMACHY measurements on the structure of theozone layer of the entire atmosphere. SCIAMACHY is a measurementinstrument onboard the environmental satellite ENVISAT. It givesinformation on the composition of the atmosphere, for example on theamount of ozone. De structure of the ozone layer is represented by ozoneprofiles. SCIAMACHY profile measurements are made by scanning theatmosphere horizontally layer by layer (limb measurements). Limb ozoneprofiles measured with SCIAMACHY have been validated by comparing them tovery reliable ozone measurements from the ground (lidar). Thisvalidation shows that individual SCIAMACHY ozone profiles can differ fromlidar measurements with 35 percent or more. The average difference is -8to 5 percent.Ozone concentrations, measured world wide and over a long time period,give information on the condition of the ozone layer and with that on theeffectiveness of ozone reduction measures.SCIAMACHY profile measurements are hampered because ENVISAT's attitudewith respect to the earth is not sufficiently known. As a result, theaccurate altitude at which SCIAMACHY measures is not well enough known. This leads to so-called altitude shifts that influence the results of themeasurements. The investigation has shown for the first time withSCIAMACHY measurements that the altitude shifts are more complicated thanthought before. This makes a correction on the measurements even moredifficult. However, it gives more insight into the unclearness ofENVISAT's attitude with respect to the earth. If a solution is found, itcan be implemented with retroactive effect (till 2002) on all SCIAMACHYprofile measurements.
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