Available calibration methods

The following calibration methods are available for imaging recipes.

• baseshift -- Use the given comma-separated doublet (i.e. 0,0) as the frame's base position. This is used to locate faint sources in the mid-infra-red data where centroiding fails when there is some telescope pointing error (such as incorrect instrument apertures). It is calibrated within NOD_CHOP_APHOT on a bright standard, and used by NOD_CHOP_FAINT. For a well-tuned system, the baseshift is expected to be near 0,0, so the centre of the detector is at the reference position (derived from the FITS headers).

• bias -- Use the given bias frame.

• dark -- Use the given dark frame.

• fpcentre -- Use the given Cartesian pixel centre of the Fabry-Perot transmitted region (UFTI only).

• flat -- Use the given flat frame.

• mask -- Use the given bad-pixel mask.

• polrefang -- Use the specified polarimetry calibration angle, converting measured polarisation vector orientations into position angles. It is measured in degrees, applied clockwise to the vector direction to allow for the orientation of the analyser with respect to north.

• readnoise -- Use the given value for the detector readnoise in electrons.

• referenceoffset -- Use the comma-separated doublet (i.e. 0,0) as the frame's reference offset, which is difference between the frame centre and the reference pixel derived from the FITS headers.

• rotation -- Use the given frame as a rotation matrix. This is no longer used in the imaging recipes.

• sky -- Use the given sky frame.