• White Light Source (WLS).


  • Unbinned WLS calibration measurement.
  • Monitoring of detector Pixel to pixel Response Non-Uniformity (PRNU) as a function of wavelength.
  • Monitoring of bad and dead detector pixels.


  • Eclipse side of the orbit.


  • From launch onwards, once per week.


WLS unbinned calibration measurement. First a number of dark measurements are performed (ICID 20), then a number of light measurements. It takes 8*2=16 seconds to read out one complete image. These unbinned measurements are well suited to determine / monitor the detector pixel to pixel non-uniformity (PRNU) and the detector bad and dead 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 (ICID 20) 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.