This is the SCIAMACHY m-factors main page.
M–factors are used in the 0-1b processor to compensate for the
radiometric degradation of SCIAMACHY
general, an m-factor is defined as the ratio between a measured
spectrum of a constant light source (typically the sun) at a certain
time to a spectrum obtained for the
same optical path at a reference time. M-factors therefore provide an
end-to-end degradation correction for each individual light path.
Schematic view of the different SCIAMACHY monitoring light paths.
M–factors have an impact on the polarization correction and on the
absolute radiometric calibration.
The m–factors for the science detectors are multiplicative factors to
the absolute radiometric calibration of SCIAMACHY.
The m–factors for the PMDs influence in a non-linear way the
polarization correction of SCIAMACHY.
Regarding the m–factors for the polarization requires re-processing of
the full mission, as the calculation of the polarization correction has
done by the Level 0-1b processor.
The concept for calculation and provision of m-factors foresees two
- A short-term solution where only science detector readouts
- A long-term solution where all light paths are corrected.
Details about the generation of m-factors are given in a corresponding Technical Note
based on partly calibrated Level 0 data
The m-factor impact on polarization correction is neglected within the
The m–factors are provided by an external
database, which than can be applied by a modified Level 1b-1c
Advantages of this approach are:
- The application of m-factors can be switched on and off by
the Level 1 data users.
- M-factors are decoupled from the operational 0-1b
therefore a fast implementation is possible.
- Updates of the m-factor data base are possible independent
from a Level 1 re-processing.
Only the m-factors describing the degradation of the science
channels are needed here; the PMD m-factors are set to 1.
On long-term, a full set of m-factors including PMDs can be
set up. For this concept, changes of the Level 0-1b processor are
m-factors are included in the Level 1 product and cannot be switched
off, if polarization correction or
absolute radiometric calibration is needed.
Advantage of this approach is full consistency
for reprocessed products.
Currently only m-factors for the
short-term solution are available.
to download the data base.
- K. Bramstedt, Calculation of SCIAMACHY M-Factors, Technical
Note, IFE-SCIA-TN-2007-01-CalcMFactor, Issue: 1,
file, ca. 1.3 MB)
If you are interested in more information on SCIAMACHY m-factors
or Klaus Bramstedt
Author of this page: Stefan