• White Light Source (WLS).


  • WLS calibration measurement with binning factor 8 (global).
  • Monitoring of long-term radiometric stability and potential degradation as a function of wavelength.
  • Monitoring of long-term detector stability as a function of wavelength.
  • Monitoring of bad and dead detector pixels on binned pixels (binning factor 8).


  • Eclipse side of the orbit.


  • From launch onwards, once per week, five times per month.


WLS calibration measurement with binning factor 8 (global). First a number of dark measurements are performed (ICID 28), then a number of light measurements. These binned measurements are well suited to determine / monitor the long-term detector stability and optical stability and potential degradation effects as a function of wavelength in time. In addition, it is also possible to monitor detector bad and dead (binned) pixels. The WLS output drifts in time after switch on. For this reason it is very important that different measurement sequences are identical, which is the case. The output reproducibility from one switch on to the next is then very good, e.g. better than 0.5%. The WLS is particularly well suited for long-term reproducibility measurements over long time periods, less so for accurate relative measurements within one measurement series (orbit), such as electronic gain ratio measurements and non-linearity measurements, for which the LED is better suited. The corresponding dark (background) measurements of ICID 28 are available for background correction in case this would be required. The background correction is also performed in the 0-1 data processor. The WLS measurements are stored in the level-1b calibration data product.