Spitzer Documentation & Tools
IRAC Instrument Handbook


Appendix A.      Pipeline History Log




1. Recalibration of IRAC fluxes in channels 3 and 4

In the process of performing a detailed cross comparison of the calibration of Spitzer instruments and comparing the IRAC calibration to the HST calibration database, an error was identified in the S18.18 IRAC processing. In updating the flux conversions (FLUXCONV), erroneous color corrections were used for the calibration stars. The color corrections used were incorrect for the 5.8 and 8.0 micron bands. The S18.18 flux values were multiplied by 1.000, 1.000, 0.968 and 0.973 for the 3.6, 4.5, 5.8 and 8.0 micron channels, respectively. The headers were also updated to indicate pipeline version S18.24 and revised flux conversion values.





1. Saturation Correction in Pipeline

Saturation is now corrected before artifacts. Artifact correction for saturated sources is now possible. The criteria for selecting sources for correction were changed. The source selection is now frame time dependent. Bit 13 in imask is changed to bit 4 after correction has been performed.

2. Imask Updates

Imask header is now formatted in a way similar to the BCD header and includes information about the various bits that may have been set.

3. ABADDATA Now Often Corrected

Frames with ABADDATA set in raw file headers are now corrected. This problem is due to shifting the data by one pixel after an extra word was read into the data. If only one such instance occurs in a frame it is now corrected. Frames with multiple instances are not corrected. The BCDs will include a header keyword BADPIX. If BADPIX = T, then another header keyword ZEROPIX gives the number of bad pixels. If ZEROPIX = 1, then header keyword ZPIXPOS gives the position of the pixel that was fixed and header keyword BADFILL gives the value (in DN) of the fixed pixel.

4. New Added Header Keywords

Barycentric Julian Date calculated with SCLK precision is now included in header keyword BMJD_OBS. Also, a new header keyword AORHDR has been added. This keyword is true if the entire AOR in which the frame was taken (not just the frame itself, such as the first frame in every AOR) was taken in the high-dynamic-range (HDR) mode.





1. Saturation Correction Update

Only sources in the 2MASS Point Source Catalog are now corrected (extended sources, such as the nuclei of bright galaxies are not corrected). Bit 13 in imasks is now flipped to zero after the saturation has been corrected.

2. Mosaic of Imasks

Mosaics of all the imasks for a given frame time in a given AOR are now produced by the pipeline and placed in the PBCD directory (mmsk files).

3. Dmasks No Longer Archived

We no longer provide dmasks as they contain misleading and incomplete information. The imasks are more robust, include flagging of various artifacts that are not present in dmasks and make full use of the saturation correction made by the pipeline.

4. Higher Accuracy Pointing Refinement

Pointing refinement is now done with the help of the 100x sampled PRFs, leading to a more accurate pointing solution.





1. A New Saturated Source Fitter

The pipeline now attempts to systematically find all saturated point sources in the images and fit them using an appropriate PSF that is matched to the unsaturated wings of the source. The new module replaces the saturated point source with an unsaturated point source that has the correct flux density of the point source. Please note that the new module does not successfully fit super-saturated point sources or point sources that are too close to the edge of the field of view for proper fitting. Only the CBCD files are saturation corrected (not the BCD files). The saturated pixels that have been replaced are identified within the bimsk (imask) files (bit 13).

2. A New Muxstripe Remover

Muxstriping (due to very bright objects in channel 1 or 2 fields of view, usually exhibiting itself as a depressed bias level in every fourth column in a section of an IRAC image) is now fit and corrected in a new pipeline module. The noise of the affected pixel area is compared to the unaffected pixels in the frame and a deviation is removed, without changing the background level or the flux in the pixels. Occasionally this correction fails and the muxstriping is unchanged. Only the CBCD files include this correction, not the BCD files.

3. Pmask Bits Now Included As Part of Imasks

See the imask bit definition in Section 7.1 of the IRAC Instrument Handbook for the definition of the various bits.

4. Mosaic Mask Files Now Available

The PBCD mosaics created in the pipeline now have associated mask files. The imasks associated with the CBCDs that were used for the creation of the mosaic have been combined to create the mask file, so the bit values can be deduced from the imask bit definition table.

5. Improved First-Frame Correction

More appropriate skydarks are now used in the pipeline, producing an improved first-frame effect correction.





1. Muxbleed Correction Update

The correction of the muxbleed effect in the BCD frames was updated. After extensive testing a new functional form and scaling law was developed for muxbleed correction in channels 1 and 2. The new functional form and scaling law correct muxbleed better than before.

2. MOPEX Now Using the bimsk.fits Files

In creating the final mosaic image, *maic.fits, the MOPEX pipeline now uses the *bimsk.fits files as input, instead of the *dmsk.fits files. The *bimsk.fits files have more relevant information useful for flagging when building mosaics and analyzing the images.

3. Header Information Updated

WCS CD matrix keywords were added to the Post-BCD file headers. The CDELT1, CDELT2, and CROTA2 keywords have been preserved but were placed in comments to avoid any confusion when handled by astronomical software. The following keywords were added to the BCD, CBCD, and Post-BCD image files: PXSCAL1, and PXSCAL2, and PA. The keywords are the pixel scale along axis 1 and axis 2 in arcsec/pixel and the position angle of axis 2 (East of North) in degrees. Keywords containing additional information on the AOR mapping parameters have been added in a separate section of the header.