• Sun irradiance over the regular aluminium reflection diffuser.


  • Global sun irradiance measurements over the regular aluminium reflection diffuser.
  • Monitoring of absolute radiometric irradiance calibration.
  • Monitoring of potential in-flight optical and/or detector degradation.
  • Monitoring of irradiance goniometry calibration (azimuth and elevation angle dependence).
  • Monitoring of spectral calibration.
  • Monitoring of spectral and spatial diffuser features.


  • Near the north pole, first light measurements, then dark measurements.


  • From launch onwards, once per week.
  • As a result of an anomaly in the Folding Mirror Mechanism (FMM) no ICID 18 measurements were performed from 27 February 2006 up to (including) 7 June 2006. After this period the anomaly was resolved and the regular measurement schedule of one measurement per week was resumed.


Sun over regular aluminium reflection diffuser global measurement. First, 77 light measurements are performed at changing elevation angles (roughly in the range +4.0 degrees to -4.0 degrees), then 77 dark measurements are performed. As a function of the day in the year (season) the azimuth angle on the diffuser changes. These measurements are used for calibration purposes only and do not enter directly into any level-1b data product. The dark (background) measurements of ICID 19 are eventually used to correct these light measurements in the 0-1 data processing.