ICID 51 => DARK_SUN_VOLUME_SPATIAL
- Dark (background) measurements corresponding to sun irradiance (quartz volume reflection diffuser) measurements of ICID 50.
- Spatial zoom-in dark (background) measurements corresponding to sun light measurements.
- Near the north pole, first light measurements, then dark measurements.
- From launch onwards, once per month.
Dark (background) measurements with the exact same instrument settings as the SUN_VOLUME_SPATIAL light measurement of ICID 50. The dark (background) measurements are performed near the north pole directly after the sun light measurements with the Sun Aperture Mechanism (SAM) closed and with the Folding Mirror Mechanism (FMM) in the position that blocks all Earth light. The dark (background) measurements are eventually used to correct the light measurements in the 0-1 data processing.