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VII. 3-Band Cryo Data Release

2. 3-Band Cryo Data Products

The WISE 3-Band Cryo Data Release products are comprised of data taken during the mission's 3-Band Cryo survey phase. This phase covers the time following the exhaustion of solid hydrogen in the WISE payload outer cryogen tank, while the detectors and telescope were still cooled by the inner cryogen tank. During this time, WISE's W1, W2 and W3 bands were operational and continued to acquire useful data, but the W4 detector was saturated by thermal emission from the warming telescope. The sensitivity achieved in the W1 and W2 bands was similar to that during the full cryogenic mission phase. The W3 measurement sensitivity was degraded and decreased steadily during the 3-Band Cryo phase because of the increasing telescope temperature and decreasing exposure times.

WISE scanned approximately 30% of the sky during the 3-Band Cryo survey phase continuing with the same strategy that was used during the full cryogenic survey. WISE scanned along lines of constant ecliptic longitude from near one ecliptic pole to near the other pole with a scan rate close to the orbital rate of 3.8 arc-minutes/second in order to always point away from the Earth. Each semi-circular track from ecliptic pole to ecliptic pole is called a scan. During each scan WISE took a frameset every 11 seconds. Each 3-Band Cryo frameset contains three images, one for each of the W1, W2 and W3 bands, with all bands observing the same 47x47 arc-minute square patch of sky. Images within each frameset were rejected and not included in the higher level data products if they were streaky due to spacecraft acceleration or if scattered Moon light was too strong, a problem that was worse at long wavelengths.

The highest level data products are the:

  1. co-added Image Atlas, which has been match filtered to maximize signal-to-noise, and
  2. Source Working Database of over 261 million detections made on the Atlas Images with signal-to-noise ratio greater than approximately 3.5 in at least one WISE band.

The lower-level data products included in the release are the Single-exposure images (Level 1b) and a Database of all the object detections on the Single-exposure image. This database is very useful for variability studies. The Single-exposure images and object detection database include lower quality frames that were not used for making the higher level products.

Last Updated: 2012 July 11

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