SCIAMACHY Absorbing Aerosol Index – calibration issues and global results from 2002–2004

[摘要] The validity of the Absorbing Aerosol Index (AAI) product from theSCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY(SCIAMACHY) is discussed. The operational SCIAMACHY AAI product suffersfrom calibration errors in the reflectance as measured by SCIAMACHY andneglect of polarisation effects in the AAI computational algorithm.Therefore, the AAI product was recalculated, compensating for theerrors, with reflectance data from the start of measurements ofSCIAMACHY until December 2004. Appropriate correction factors weredetermined for the UV to correct for the radiometric error in theSCIAMACHY reflectances. The algorithm was provided with LookUp Tables inwhich a good representation of polarisation effects was incorporated, asopposed to the LookUp Tables of the operational product, in whichpolarisation effects were not accounted for. The results are presented,their validity discussed, and compared to the operational product andindependent AAI data from the Total Ozone Mapping Spectrometer (TOMS).The AAI is very sensitive to calibration errors and can be used tomonitor calibration errors and changes. The AAI is sensitive to sunglintand a correction flag used for the AAI is presented. From 2004 onwards,the new SCIAMACHY AAI is suitable to add to the continuation of thelong-term AAI record. Important changes in the long-term AAI record dueto instrument and algorithm changes are highlighted. Recommendations aregiven for improvement of the operational AAI product.

[学科分类] 大气科学