Calibration data for VISIR are taken for two purposes:
assess the instrumental status
calibrate SCIENCE data.
VISIR calibration data are taken at night (e.g. standard star
observations) and as daytime calibrations. On request of
the user, also nighttime calibrations can be obtained as part of the
Observing Block which generates the SCIENCE data ("attached
calibrations"). Since the beginning of operations all the daytime calibrations have only been used to monitor health of the instrument.
All calibration data taken in VISIR are processed by QC Garching to
obtain calibration solutions. These solutions come as
calibration product fits file frames (e.g. standard star imaging frames)
calibration product fits tables (e.g. spectrum extracted in a form of a table)
At present, all sets of VISIR calibration frames are reduced
independently, i.e. there is no calibration cascade. In the future the
flatfield correction may be included. It's still under investigation.