6.2.2 Relevant calibration parameters
Only a very short overview for the calibration is given here. For details the reader is directed to the Level 0-1c Algorithm Technical Basis Document (ATBD). All corrections can be applied by using the SciaL1c tool (see Annex 1).
220.127.116.11 Memory Effect and Non-Linearity correction
The UV/VIS and the SWIR detectors require different detector corrections. The UV/VIS channels have a memory effect, i.e. they “remember” the previous illumination and a small signal is left in the next readout, depending on the signal level. The SWIR detectors 6-8 show a non-linearity depending on the signal level of the incoming signal. Both corrections are parameterized as a function of the electronic signal on the detector and were measured in-flight and on-ground. The memory effect correction can be described as one function per channel for all pixels. The non-linearity can be described with four functions per channel for odd pixels, even pixels and pixels with a number higher and lower than 512 (the middle pixel). The functions are part of the key data. In the Level 1b product the correction value for each pixel is contained within one byte as a compressed value.
18.104.22.168 Dead and Bad Pixel Mask
The SWIR channels 6-8 suffer from a rising number of bad pixels that are not (or only to a small degree) usable for retrieval. The reason was a lattice constant mismatch between the substrate material and the light detecting material of the detectors. The bad pixels are detected using dark, WLS and sun measurements. Several thresholds for the three were determined to separate bad from good pixels. The number of bad pixels rised with the life time of the instrument due to proton impact. The mask is calculated for each orbit and stored in the Pixel-to-Pixel Gain (PPG) ETALON ADS.