Calibration Coefficients computation for IR Channels

The Calibration Coefficients Computation for IR Channels process calculates the calibration offset and gain that describe the linear relationship between pixel count and radiance for the thermal IR channels. These parameters are determined from the mean value of the Black Body (BB) pixel counts acquired during the calibration period and the mean BB temperatures of the same calibration period.

The calibration period is defined as the short interval of time in which the appropriate mean calibration coefficients are computed and applied to all packets belonging to this period – it is nominally set to 10 scan cycles.

Six sub-steps are defined:

  1. Calculate the weighted mean thermometer values for each BB, for each calibration period.
  2. Convert each weighted mean temperature to a radiance value for each IR channel.
  3. Correct the BB radiance value using the mean background temperature.
  4. Compute mean pixel counts.
  5. Calculate gains and offsets for each calibration period.
  6. Compute the radiometric noise of the instrument, expressed as noise equivalent brightness temperature difference (NEDT), computed for all IR channels.


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