Impact of Level 1 quality on BIRRA CO retrieval
Günter Lichtenberg(1), Sebastian Gimeno-Garcia(1), Franz Schreier(1), Sander Slijkhuis(1), Ralph Snel(2), Richard van Hees(2) and Piet van der Meer(2)
(1) German Aerospace Center, Münchner Str. 20, 82234 Weßling, Germany
(2) Netherlands Institute for Space Research (SRON), Sorbonnelaan 2, 3785 CA Utrecht, Netherlands
The SCIAMACHY near infrared (NIR) channels 6-8 are suitable to
retrieve vertical column densities (VCDs) of atmospheric gases such as
CO, CH4, CO2 or H2O. BIRRA will be used in the coming version 5 of
the offline Level 1b to 2 SCIAMACHY processor to retrieve CO values
The quality of VCD retrievals depends on theoretical, computational
and observational issues. Realistic atmospheric data as
well as efficient yet accurate, robust radiation transfer models
and inversion methods have to be used. However, especially operational
applications require to keep computational time within strict limits
and the best possible models are chosen according to this restriction.
The quality of the measured spectra greatly affects the accuracy of the
retrievals. Since model parameters are optimally varied during the inversion
process to mimic the measured values, errors in the input spectra will
lead to wrong retrievals.
SCIAMACHY spectra are spectrally and radiometrically calibrated and
corrected for several effects, namely: Leakage current,
pixel-to-pixel gain, non-linear response, straylight, polarisation.
Reflectances are calculated using inflight sun diffuser spectra. Additionally,
the degradation of the instrument is being monitored and the quality of the
individual spectral pixels assessed. It turned out that the effect of the
bad/dead pixel mask (BDPM) has a major impact on the retrievals.
Focussing on carbon monoxide, this work aims at studing the effect of
different calibration steps on the retrieval of atmospheric gas