SCIAMACHY Absorbing Aerosol Index – calibration issues and global results from 2002–2004 M. de Graaf and P. Stammes Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE De Bilt, The Netherlands
Abstract. The validity of the Absorbing Aerosol Index (AAI) product from the
SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY
(SCIAMACHY) is discussed. The operational SCIAMACHY AAI product suffers
from calibration errors in the reflectance as measured by SCIAMACHY and
neglect of polarisation effects in the AAI computational algorithm.
Therefore, the AAI product was recalculated, compensating for the
errors, with reflectance data from the start of measurements of
SCIAMACHY until December 2004. Appropriate correction factors were
determined for the UV to correct for the radiometric error in the
SCIAMACHY reflectances. The algorithm was provided with LookUp Tables in
which a good representation of polarisation effects was incorporated, as
opposed to the LookUp Tables of the operational product, in which
polarisation effects were not accounted for. The results are presented,
their validity discussed, and compared to the operational product and
independent AAI data from the Total Ozone Mapping Spectrometer (TOMS).
The AAI is very sensitive to calibration errors and can be used to
monitor calibration errors and changes. The AAI is sensitive to sunglint
and a correction flag used for the AAI is presented. From 2004 onwards,
the new SCIAMACHY AAI is suitable to add to the continuation of the
long-term AAI record. Important changes in the long-term AAI record due
to instrument and algorithm changes are highlighted. Recommendations are
given for improvement of the operational AAI product.
Citation: de Graaf, M. and Stammes, P.: SCIAMACHY Absorbing Aerosol Index – calibration issues and global results from 2002–2004, Atmos. Chem. Phys., 5, 2385-2394, doi:10.5194/acp-5-2385-2005, 2005.