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Relevant Auxiliary Data

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6.2.3 Relevant Auxiliary Data

The auxiliary files contain data that are external input to the processing either because they were measured independently (e.g. during on-ground calibration) or because they are measured less frequently (e.g. daily sun measurements). Auxiliary data files (ADF) are calculated by the SciCal tool and stored in the IECF data base. The IPF then copies them to the level 1b files into the Global Annotation Data Set (GADS). All auxiliary data necessary to generate a calibrated level 1c product are stored in the level 1b product itself with the exception of the m-factor file. The m-factor files for the mission can be obtained at this address: SCIAMACHY m-factors (http://www.iup.uni-bremen.de/sciamachy/mfactors/downloads.html)

Once the m-factor files are locally stored, the SciaL1c user tool can be used to apply the m-factors. If only the location of the m-factor files is given, the file is chosen in the same way as in the operational processing. Additionally the user has the option to specify the file that should be used to read in the correction factors.

6.2.4 Degradation Correction: m-factors

M–factors are used in the 0-1b processor to compensate for the radiometric degradation of SCIAMACHY. In 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. (fig. 6-3)

 

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fig. 6-3:

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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 to be done by the Level 0-1b processor. The concept for calculation and provision of m-factors foresees two steps:


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A short-term solution where only science detector readouts are corrected.

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A long-term solution where all light paths are corrected.

 

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