ICID 141 => LONG_DARK_UNBINNED_SHORTDURATION_GC3

Illumination:

  • Dark.

Purpose:

  • Unbinned long-duration dark measurement.
  • Determination / monitoring of pixel dark current.
  • Monitoring of bad and dead detector pixels.
  • Monitoring / calibration of Random Telegraph Signal (RTS) effects.

Location:

  • Eclipse side of the orbit.

Usage:

  • From 9 March 2005 (orbit number 3457) onwards, once per day.
  • As a result of an anomaly in the Folding Mirror Mechanism (FMM) no ICID 141 measurements were performed from 28 February 2006 up to (including) 11 June 2006, with only one measurement at 6 June 2006. After this period the anomaly was resolved and the regular measurement schedule of one measurement per day was resumed.

Description:

Unbinned long-duration dark calibration measurement. These unbinned measurements are well suited to determine / monitor the unbinned detector bad and dead pixels and the dark current of the individual pixels. The ICID 141 measurements are the long-duration dark measurements with a comparatively short exposure time. The measurements are used together with the long-duration dark measurements with a comparatively long exposure time of ICID 142. Since launch 2 similar long-duration unbinned dark measurements are used: ICIDs 12 and 13. These are similar to ICIDs 141 and 142, but they have higher electronic gain factors, which may result in saturation. The electronic gain code for ICIDs 141 and 142 is 3, i.e. gain factor x4.
ICID 103 is an unbinned long-duration dark measurement with an intermediate exposure time. This ICID 103 was added to the daily measurement scenario on 9 March 2005 (orbit number 3458) in order to study the proton radiation effects in the South Atlantic Anomaly (SAA) in the vicinity of Brazil.
High-energetic protons (>10 MeV) trapped in the magnetic field of the Earth can cause damage to the CCD detector pixels. This damage manifests itself as increased dark current and Random Telegraph Signal (RTS) effects, the jumping of the dark signal level between two or more quasi-stable levels. These effects have to be corrected for in the in-flight calibration and in the 0-1 data processing. With these corrections the pixels affected by proton radiation damage can still be used for science purposes. Only for a small fraction of the pixels the effects of the proton radiation damage are so severe that these pixels need to be flagged in the level-1b radiance and irradiance data products. This small fraction of pixels, flagged as bad pixels, shall not be used for science purposes. The ICIDs 141 and 142 measurements are used to study the RTS effects in flight.
The dark measurements of ICID 141 are performed with the Folding Mirror Mechanism (FMM) in the position that blocks the Earth optical path. The dark measurements are stored in the level-1b calibration data product.