Reference File

The dark current step uses a DARK reference file.

CRDS Selection Criteria

Dark reference files are selected on the basis of INSTRUME, DETECTOR, and SUBARRAY values for the input science data set. For MIRI exposures, the value of READPATT is used as an additional selection criterion.

DARK Reference File Format

Dark reference files are FITS files with 3 IMAGE extensions and 1 BINTABLE extension. The FITS primary data array is assumed to be empty. The characteristics of the three image extensions for darks used with the Near-IR instruments are as follows:

EXTNAME	NAXIS	Dimensions	Data type
SCI	3	ncols x nrows x ngroups	float
ERR	3	ncols x nrows x ngroups	float
DQ	2	ncols x nrows	integer

The dark reference files for the MIRI detectors depend on the integration number, because the first integration of MIRI exposures contains effects from the detector reset and are slightly different from subsequent integrations. Currently the MIRI dark reference files contain a correction for only two integrations: the first integration of the dark is subtracted from the first integration of the science data, while the second dark integration is subtracted from all subsequent science integrations. The format of the MIRI dark reference files is as follows:

EXTNAME	NAXIS	Dimensions	Data type
SCI	4	ncols x nrows x ngroups x nints	float
ERR	4	ncols x nrows x ngroups x nints	float
DQ	4	ncols x nrows x 1 x nints	integer

The BINTABLE extension in dark reference files contains the bit assignments used in the DQ array. It uses EXTNAME=DQ_DEF and contains 4 columns:

• BIT: integer value giving the bit number, starting at zero
• VALUE: the equivalent base-10 integer value of BIT
• NAME: the string mnemonic name of the data quality condition
• DESCRIPTION: a string description of the condition