Comparison of Absorbing Aerosol Index products from GOME-2 and SCIAMACHY

In this paper we present validation results obtained from a direct comparison between the Absorbing Aerosol Index (AAI) measured by GOME-2 (on MetOp-A) and SCIAMACHY (on Envisat) at roughly the same time and place. Because of the slightly different orbital periods, such an intercomparison is not possible for all days of the year. However, for many days on which intercomparison is possible, the orbit tracks overlap completely, ensuring that the scattering geometries (that is, the viewing and solar angles) are nearly identical, which increases the of accuracy and the credibility of the intercomparison. The agreement between the two AAI products is found to be quite good, with systematic differences of less than 0.1 index points over the entire overlapping time range (2007-2012).