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Description
Planck is ESA's third generation space based cosmic microwave background
experiment, operating at nine frequencies between 30 and 857 GHz and was
launched May 2009. Planck provides all-sky survey data at all nine
frequencies with higher resolution at the 6 higher frequencies.
It provides substantially higher resolution and sensitivity
than WMAP. Planck orbits in the L2 Lagrange point.
<p>
These data come from the legacy Release 3 of the Planck
mission.
<p>
These products include polarization information available to
visualize in several ways. The data contain Stokes parameters I, Q,
and U, and in addition to these, it is possible to visualize the
polarized intensity PI=sqrt(Q^2+U^2) and the polarization angle
PA=1/2atan(U/Q). Note that at their native resolution of a few
arcmin (depending on the frequency), these polarization data will
appear very noisy. In order to visualize the polarization
information, it is highly recommended that the data be resampled
with the "Clip (intensive)" sampler and the result smoothed. That
sampler will average all the data points within a given output pixel
rather than the more common nearest neighbor. It will do this averaging before
computing either PI or PA to reduce the effects of the noise. This
sampler is set as the default for this survey. If the output pixel
resolution is not significantly larger than the resolution, a smoothing of the
output pixels will also be necessary.
<p>
Note also that Q and U are defined relative to a given co-ordinate
system, in this case Galactic, and following the
CMB convention (not the IAU); see
https://lambda.gsfc.nasa.gov/product/about/pol_convention.cfm. This
means that they will appear to vary rapidly near the pole of that coordinate
system. The PI and PA will be computed correctly for any position
on the sky.
<p>
The original data are stored in HEALPix pixels. SkyView treats HEALPix as a standard
projection but assumes that the HEALPix data is in a projection plane with a rotation of -45 degrees.
The rotation transforms the HEALPix pixels from diamonds to squares so that the boundaries of the
pixels are treated properly. The special HealPixImage class is used so that SkyView can use
the HEALPix FITS files directly. The HealPixImage simulates a rectangular image but
translates the pixels from that image to the nested HEALPix structure that is used
by the HEALPix data. Users of the SkyView Jar will be able to access this survey through the web
but performance may be poor since the FITS files are 150 to 600 MB in size and must be completely
read in. SkyView will not automatically
cache these files on the user machine as is done for non-HEALPix surveys.
</p>
Data from the frequencies of 100 GHz or higher are stored
in a HEALPix file with a resolution of approximately 1.7' while lower frequencies are stored with
half that resolution, approximately 3.4'. Provenance: Data split using skyview.survey.HealPixSplitter from the PR3 distriuted by the Planck Science team.. This is a service of NASA HEASARC.
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