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Description
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.
The NEOWISE Post-Cryo Data Release products were generated using data taken during the mission's Post-Cryo survey phase. This phase covers the time following the exhaustion of solid hydrogen in the WISE payload inner cryogen tank, when the detectors and optics gradually warmed until they reached a stable equilibrium temperature near 73.5 K (VIII.1.a.i). During this time, WISE's W1 and W2 detectors continued to acquire high quality imaging data with sensitivities close to that during the mission's cryogenic survey phases. The W3 and W4 detectors were fully saturated by the thermal emission from the warming telescope.
WISE scanned approximately 70% of the sky during the Post-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 Post-Cryo frameset contains two images, one for each of the W1 and W2 bands, both observing the same 47x47 arc-minute square patch of sky.
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