• Sun irradiance over the quartz volume reflection diffuser.


  • Spatial zoom-in sun irradiance measurements over the quartz volume reflection diffuser.
  • Provides spatial zoom-in sun irradiance level-1b data product for normalisation of Earth radiance spectra to obtain sun-normalised Earth radiances, or absolutely calibrated Earth reflectances.
  • 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 month.
  • As a result of an anomaly in the Folding Mirror Mechanism (FMM) no ICID 50 measurements were performed from 10 February 2006 up to (including) 16 June 2006. After this period the anomaly was resolved and the regular measurement schedule of one measurement per month was resumed.


Sun over quartz volume reflection diffuser spatial zoom-in 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. The individual sun irradiance measurements in the elevation angle range between -3.0 degrees and +3.0 degrees are averaged in the 0-1 data processor to obtain the level-1b irradiance data product. Averaging is performed to reduce the impact of spectral and spatial diffuser features and to improve the signal-to-noise. The dark (background) measurements of ICID 51 are eventually used to correct these light measurements in the 0-1 data processing.