Spitzer Documentation & Tools
IRAC artifact mitigation

Purpose: A set of procedures to mitigate electronic artifacts in IRAC data.

Author: Sean Carey
Date Contributed: 2 Sep 2005
System Requirements: IDL v5.4 or higher; astrolib IDL library

These procedures have now been incorporated into the IRAC pipeline to create the *cbcd.fits files packaged with your downloaded BCD data. If you would like to be notified of code updates and patches, please email Sean Carey (carey{@}ipac.caltech.edu (remove the {} from the address first)).

Information and Download

For software download and a complete description of the software, including operating instructions, see the IRAC Artifact Mitigation Info page

For a complete description of artifacts in IRAC data please consult the IRAC Data Handbook. The code does not work on subarray data. In general, subarray data is free of the artifacts this code will correct. The artifact mitigation code attempts to correct:

  • Muxbleed: Residual signal in multiplexers seen in 3.6 and 4.5 micron data
  • Column pulldown/pullup: A bias shift in a column containing a bright source. Effects are seen in data from all arrays
  • Electronic banding: A bias shift in a row containing a bright source. This effect is seen in the 5.8 and 8.0 micron arrays only.
  • First frame effect: The overall bias of each array has a temporal dependence (the bias depends on the readout history of the array). The bias variation between overlapping images is corrected in a least-squares fashion. Another method of correcting for bias variations is provided as part of the post-BCD software package (MOPEX task overlap.pl). In many cases the overlap.pl script will produce comparable results to the overlap correction provided by this software.

The code does not correct:

  • Muxstriping: A bias variation (3.6 and 4.5 micron arrays only) seen after observing very bright sources which manifests itself as a per readout bias shift which affects only a fraction of the array.
  • Optical banding: Some of the light from point sources observed at 5.8 and 8.0 microns is scattered into the columns and rows near the peak of the source. The optical component of banding is only partially corrected by this code as the code assumes that a source does not create artifacts in rows and columns other than the one containing the triggering pixel.
  • Stray light: Stray light is masked at a later stage in the processing using the mask_straylight procedure written by Mark Lacy. The straylight masked is bundled with the artifact correction routines, but is not used in the make_corrected_bcds.tcsh script.
  • Ghost images: Ghost images are not mitigated by this code. The stray light masking code will also mask filter ghosts in all 4 arrays. The optical ghosts are currently included in the PRFs provided here.