Wide-field Infrared Survey Explorer
When DID WISE observe a source?
WISE generally observed a semi-circle at an ecliptic longitude
95o larger than the ecliptic longitude of the Sun (blue
curve below), and another semi-circle at an ecliptic longitude
90o smaller than the ecliptic longitude of the Sun (red
curve below). The asymmetry allows WISE to recover from a brief safing
event by decreasing the ecliptic longitude of the scan circles by
1o per day of duration for the safing event. This does not
cause WISE to scan any closer to the Sun.
The graph above shows the actual ecliptic longitude of the scan
semi-circles as a function of day of 2010, for actually executed
survey scans.
There were small toggles on every other orbit to smooth out the
influence of the South Atlantic Anomaly, and a monthly sawtooth
designed to get data before or after the Moon crosses the scan circle.
While WISE plans to never look at the Moon, we will collect and throw
data with the Moon closer than 15o to the line-of-sight.
The monthly sawtooth motion covers these Moon affected regions twice so
the WISE catalog will not have holes caused by the Moon.
Just as the Moon crosses the scan circle the longitudes are modified to
keep 5o away from the Moon.
Some test scans were executed trying to exactly match previous or
planned scans in order to measure non-linearity in the arrays, leading
to the stray dots not on the plan.
It should be possible to find the dates a source was observed by
computing its ecliptic longitude, adding a
±0.4o/cos(latitude)
range, and then finding the date(s) when the above curves are in the
source's ecliptic longitude range.
The map below shows the actual survey plus pretty good IOC coverage
in galactic coordinates:
UPDATE: The low coverage that used to be seen
along the galactic plane was caused by error returns from
the preliminary processing pipeline in this very bright and source rich
region.
As of 21 June 2010 all these data have been reprocessed so the
galactic center hole is filled in.
The actual coverage achieved in WISE band 4 (22 μm) is shown in the
map below:
Over 99.99% of the sky is covered 7 or more times, and 99.92% of the sky
is covered 8 or more times.
The actual coverage achieved in WISE band 3 (12 μm) before the increased
backgrounds from the telescope warming to 45 K required a reduction in
exposure time is shown in the map below:
Coverage continued with Band 3 at reduced sensitivity until 29 Sep 2010.
The full coverage for the cryogenic mission is shown in the map below.
Data continued to be collected in bands 1 and 2 for the NEOWISE asteroid
search program but this map shows the extent of the final data release
due in 17 months (01 Mar 2012 [TBD]):
The two band data collected from October 2010 through Jan 2011
will not be included
in the final data release but will be available as individual images.
Last modified 16 Mar 2011