VII. 3-Band Cryo Data Release

1. Introduction

d. Cautionary Notes

WISE 3-Band Cryo data products are subject to most of the same limitations and exhibit the same features as the WISE All-Sky Release Image and Source List data products. We recommend that you begin by reviewing the Cautionary Notes for the All-Sky Release Products before making use of the 3-Band Cryo Data Products.

The WISE survey data acquisition strategy, data processing and quality assurance measures were all designed to yield data products of high reliability and fidelity. However, the changing nature of the payload and detectors during the 3-Band Cryo survey phase make it difficult to produce calibrated products that have the same uniformity and fidelity of the products generated from the full cryogenic survey when the performance of the WISE payload was extremely stable. This combined with the challenge of validating such a large data set in a limited time result in a number of limitations and problems that persist into the 3-Band Cryo Release products.

3-Band Cryo Release Supplement sections VII.1.d.i through VII.1.d.vi contain descriptions of known features and limitations that pertain to WISE 3-Band Cryo Data Release products. Section VII.1.d.i below contains a list of the most important things that you should know about the Release products to make the best use of them in your research. Click on any item in the list to see a more detailed discussion.

Section VII.1.d.ii contains general information that pertain to all of the 3-Band Cryo Release products. Sections VII.1.d.iii and VII.1.d.iv contain essential information specific to the 3-Band Cryo Source Working Database and Image Atlas. Sections VII.1.d.iv and VII.1.d.v contains Cautionary Notes for users who make use of the 3-Band Cryo Single-exposure Source Database and Images. The Known Solar System Object Possible Association List is subject to the same limitations that apply to the All-Sky Release that are described in I.4.d.iv.

You are strongly encouraged to read and familiarize yourself with all of these Cautionary Notes before using the WISE 3-Band Cryo Release data products.

i. Top 10 (or so) Things You Should Know About the WISE 3-Band Cryo Release Data Products

Click on the links below to read more detailed descriptions.

1. The quality of the WISE 3-Band Cryo Release data products is generally not as good as that of the All-Sky Release products. Performance in the W1 and W2 bands is close that in the full cryogenic survey phase, but the W3 performance is significantly degraded because of increasing temperatures and reduced exposure times.


2. The WISE All-Sky Release Catalog and Atlas are the most complete and uniform compendia of the mid-infrared sky. The WISE 3-Band Cryo Release Products are most useful as a resource to learn more about objects found in the All-Sky Release products, such as possible flux variability, proper motion, and verification for very faint or confused objects.


3. The 3-Band Cryo Release products do not contain any measurements in the W4 (22 μm) band.


4. The 3-Band Cryo observations covered only 30% of the sky. See also VII.5.a.


5. There is a gap in the W3 coverage during the 3-Band Cryo survey when the W3 Single-exposure measurements began to saturate on normal sky backgrounds before the exposure times could be reduced. These W3 frames were omitted from Multiframe Pipeline processing that produced the W3 Atlas Images and Source Working Database.


6. The W3 band sensitivity varied in a complex way during the 3-Band Cryo period because of the increasing temperatures and the reduced exposure times. 3-Band Cryo W3 Atlas Images were assembled using Single-exposure images with very different depth and quality, so depth-of-coverage in the Atlas Image cannot be used as a reliable proxy for relative sensitivity. Use the 3-Band Cryo Atlas Image Uncertainty Maps to account properly for the net sensitivity in W3.


7. The 3-Band Cryo Source Working Database is not a highly reliable, well-vetted list of mid-infrared sources like the All-Sky Release Source Catalog. The 3-Band Cryo Database contains detections of real astrophysical objects, as well as spurious extractions of image artifacts and transient noise events, and redundant detections of objects in the Atlas Tile overlap regions.


8. The 3-Band Cryo Source Working Database profile-fit photometry measurements may be systematically fainter than measurements in the All-Sky Release Source Catalog. This bias increases towards fainter fluxes, and with increasing source density.


9. The 3-Band Cryo Single-exposure Images and Source Working Database W3 calibrations have ±6%, time-dependent variations with respect to the All-Sky Release calibrations. These variations were compensated for during the construction of the 3-Band Cryo Atlas Images and the Source Working Database.


10. Saturated pixels and sources may not be accurately flagged in the 3-Band Cryo Release image and extracted source databases because of the loss of on-board saturated pixel encoding. This results in erroneous flux measurements for saturated sources and incorrect flagging of spurious detections of by image artifacts from bright sources..

Last update: 2012 June 26