VIII. Post-Cryo Data Release

2. Post-Cryo Data Products

b. Single-Exposure Images, Bit Masks, Uncertainty Maps

The 2013 Post-Cryo Release image archive contains 901,271 image sets that were produced during second-pass data processing that used improved calibrations and data reduction algorithms. The Preliminary Post-Cryo Release image archive contained 901,274 images sets that were produced during first-pass processing. The 2013 Post-Cryo Release Single-exposure images supersede the Post-Cryo Preliminary Release images.

The 2013 Post-Cryo Release contains three fewer image sets than the Post-Cryo Preliminary Release because the framesets corresponding to these image sets failed processing during the second-pass. In one case, scan/frame number 09866a144, the failure was caused by severe image smearing. In the remaining two cases, 09918a195 and 10196a265, W1 images were lost during downlink and second-pass processing required both W1 and W2 images to be available for successful completion.

Each element of the Post-Cryo Single-exposure image sets is a 1016x1016 pix @ 2.75"/pix FITS format image. Each image set consists of:

• Intensity images - Two images, one in the W1 and W2 bands, that contain the calibrated sky images for each individual 7.7sec W1 and W2 exposure. Instrumental calibrations have been applied to these images to remove instrumental signatures, and the headers contain photometric zero points and full WCS information.


• Uncertainty maps - Two images that give the 1-σ uncertainty estimate for each pixel in the corresponding intensity images.


• Bit-masks - Two images, one in the W1 and W2 bands, that provide information about the status of each pixel in the Single-exposure intensity images.

WISE Post-Cryo Single-exposure images are in the Flexible Image Transport System (FITS) format and follow the World Coordinate System (WCS) standard for astronomical image data.

Single-exposure Image products have filenames as follows:

• Intensity image: frameID-wBAND-int-1b.fits


• Uncertainty image: frameID-wBAND-unc-1b.fits


• Bit-Masks: frameID-wBAND-msk-1b.fits

where BAND = 1, 2, 3, or 4, and frameID is a unique identification string pertaining to the frameset. FrameID has the form SSSSxMMM, where SSSSSx is the identifier of the scan in which the framset was taken, scan_id, and MMM is the frame number, frame_num, within the scan. BAND and frameID are variables that match the values of keywords with the same name in FITS headers. The WISE Single-exposure Image FITS header content is described in II.4.a.i.

The Post-Cryo Single-exposure (L1) Frame Metadata Table provides additional information about the WISE Single-exposure image sets including much of the image header content and derived statistical and quality assessment information pertaining to both the Single-exposure images and extracted source database. This metadata table can be searched using the IRSA Gator catalog search engine.

CAUTION: The Post-Cryo Single-exposure image archive contains all images taken during Post-Cryo operations, regardless of their quality. Many of these framesets suffer from the following problems:

• Degraded image quality due to spacecraft jitter,


• Contamination by severe scattered light artifacts from the moon and bright planets,


• Contamination by bright satellite streaks both on an off the FOV,


• Contamination by large numbers of cosmic ray strikes because they were taken while WISE was passing through the South Atlantic Anomaly (SAA),


• Contamination by electronic noise signatures.

Examples of frames that show many of these problems can be seen in the All-Sky and 3-Band Cryo Release Single-exposure Image Anomaly galleries in II.4.b.ii and VII.2.d.i.

You can identify Single-exposure image sets that are of good quality using several of the keywords in the FITS headers and/or values in the metadata tables as follows:

• qual_fact > 0 - Good overall quality score (includes image quality and pixel noise levels; available in Frame Metadata and Image Inventory Tables only)


• SAA_SEP (saa_sep) > 0 - Outside of the nominal boundaries of the SAA


• MOON_SEP (moon_sep) > 24° - Beyond the worst of the scattered moonlight (Use larger values to be more conservative)

Last update: 2013 March 14