Reference File

The superbias subtraction step uses a SUPERBIAS reference file.

CRDS Selection Criteria

Superbias reference files are selected on the basis of the INSTRUME, DETECTOR, READPATT and SUBARRAY values of the input science data set.

SUPERBIAS Reference File Format

Superbias 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 extension are as follows:

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

The BINTABLE extension 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