VII. 3-Band Cryo Data Release

2. 3-Band Cryo Data Products

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

The WISE 3-band Cryo Single-exposure image archive is comprised of 392,879 1016x1016 pix @ 2.75"/pix FITS format image sets. Each image set consists of:

• Intensity images - Three images, one in the W1, W2 and W2 bands, that contain the calibrated sky images for each individual 7.7sec (W1 and W2) and 8.8/4.4/2.2/1.1sec (W3) 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 - Three images that give the 1-σ uncertainty estimate for each pixel in the corresponding intensity images. These uncertainty maps are used to generate the Atlas Image Uncertainty maps.


• Bit-masks - Three images, one in the W1, W2 and W3 bands, that provide information about the status of each pixel in the Single-exposure intensity images.

WISE 3-Band 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 3-Band 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 3-Band Cryo Single-exposure image archive contains all images in the scans that are part of the WISE 3-Band Cryo Data Release scope (VII.4.a), 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),


• Residual long-term W3 latent images from bright sources that were not corrected by dynamic frame calibration step,


• Unusable W3 data because they were taken <2000 sec following the annealing of the Si:As detectors, and


• Contamination by electronic noise signatures.

Images showing example frames with many of these problems can be seen in the Single-exposure Image Anomaly galleries in II.4.b.ii and VII.2.d.i.

Most of the low-quality framesets and frames were excluded when selecting frames to constructed the coadded 3-Band Cryo Atlas Images and Source Working Database (VII.4.c), but all are present in the 3-Band Cryo Single-exposure image archive. Use this archive with caution.

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 South Atlantic Anomaly


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


• DT_ANNEAL (dtanneal) > 2000 sec - W3 detector has stabilized following annealing (W1 and W2 are not affected by anneals)

i. Single-Exposure Image Anomalies

Last update: 2012 July 6