Validation of SCIAMACHY limb ozone profiles with lidar

The National Institute for Public Health and the Environment (RIVM) has examined the quality of SCIAMACHY measurements on the structure of the ozone layer of the entire atmosphere. SCIAMACHY is a measurement instrument onboard the environmental satellite ENVISAT. It gives information on the composition of the atmosphere, for example on the amount of ozone. De structure of the ozone layer is represented by ozone profiles. SCIAMACHY profile measurements are made by scanning the atmosphere horizontally layer by layer (limb measurements). Limb ozone profiles measured with SCIAMACHY have been validated by comparing them to very reliable ozone measurements from the ground (lidar). This validation shows that individual SCIAMACHY ozone profiles can differ from lidar measurements with 35 percent or more. The average difference is -8 to 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 the effectiveness of ozone reduction measures. SCIAMACHY profile measurements are hampered because ENVISAT's attitude with respect to the earth is not sufficiently known. As a result, the accurate altitude at which SCIAMACHY measures is not well enough known. This leads to so-called altitude shifts that influence the results of the measurements. The investigation has shown for the first time with SCIAMACHY measurements that the altitude shifts are more complicated than thought before. This makes a correction on the measurements even more difficult. However, it gives more insight into the unclearness of ENVISAT's attitude with respect to the earth. If a solution is found, it can be implemented with retroactive effect (till 2002) on all SCIAMACHY profile measurements.