Difference between revisions of "Sky temperature maps"

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== File names ==
 
== File names ==
The FITS filenames are of the form ''{H|L}FI_SkyMap_fff_nnnn_R1.nn_{coverage}_{type}.fits'', where ''fff'' are three digits to indicate the Planck frequency band, and ''nnnn'' is the Healpix Nside of the map, ''coverage'' indicates which part of the mission is covered, and the optional ''type'' indicates the subset of input data used.  A full list of products, with links to them in the Archive, is given in the tables below.
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The FITS filenames are of the form ''{H|L}FI_SkyMap_fff{-tag}_Nside_R2.nn_{coverage}-{type}.fits'', where ''fff'' are three digits to indicate the Planck frequency band, ''tag'' indicates the single detector or the detset,  ''Nside'' is the Healpix Nside of the map, ''coverage'' indicates which part of the mission is covered (full, half mission, survey, year, ...) , and the optional ''type'' indicates the subset of input data used.  The table below lists the products by type, with the appropriate unix wildcards that form the full filename.
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{| class="wikitable"  align="center" style="text-align"left" border="1" cellpadding="15" cellspacing="20"  width=880px
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|+ '''FITS filenames'''
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|- bgcolor="ffdead"
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! Coverage  ||  filename  ||  half-ring filename
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|-
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| Full chan, full mission ||HFI_SkyMap_???_2048_R2.??_full.fits ||HFI_SkyMap_???_2048_R2.??_full-ringhalf-?.fits
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|-
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| Full channel, nominal mission ||HFI_SkyMap_???_2048_R2.??_nominal.fits || n/a
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|-
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| Full channel, single survey || HFI_SkyMap_???_2048_R2.??_survey-?.fits || n/a
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|-
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| Full channel, single year || HFI_SkyMap_???_2048_R2.??_year-?.fits  || n/a
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|-
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| Full channel, half mission || HFI_SkyMap_???_2048_R2.??_halfmission*-?.fits || n/a
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|-
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| Det-set, full mission || HFI_SkyMap_???-ds?_2048_R2.??_full.fits || HFI_SkyMap_???-ds?_2048_R2.??_full-ringhalf-?.fits
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|-
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|Single SWB, full mission || HFI_SkyMap_???-?_2048_R2.??_full.fits || HFI_SkyMap_???-?_2048_R2.??_full-ringhalf-?.fits
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|}
  
 
For the benefit of users who are only looking for the frequency maps with no additional information, we also provide a file combining the 9 frequency maps as separate columns in a single extension. The 9 columns in this file contain the intensity maps ONLY and no other information (hit maps and variance maps) is provided.
 
For the benefit of users who are only looking for the frequency maps with no additional information, we also provide a file combining the 9 frequency maps as separate columns in a single extension. The 9 columns in this file contain the intensity maps ONLY and no other information (hit maps and variance maps) is provided.
  
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{| class="wikitable"  align="center" style="text-align:center" border="1" cellpadding="3" cellspacing="0"  width=500px
 
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{{PLASingleFile|fileType=map|name=HFI_SkyMap_857_2048_R1.10_nominal_ringhalf_2.fits|link=HFI_SkyMap_857_2048_R1.10_nominal_ringhalf_2.fits}}
 
{{PLASingleFile|fileType=map|name=HFI_SkyMap_857_2048_R1.10_nominal_ringhalf_2.fits|link=HFI_SkyMap_857_2048_R1.10_nominal_ringhalf_2.fits}}
 
|}
 
|}
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--->
  
 
== FITS file structure ==
 
== FITS file structure ==

Revision as of 11:24, 10 December 2014

General description[edit]

Sky maps give the best estimate of the intensity and polarization (Stokes Q and U components), if available, of the signal from the sky after removal, as far as possible, of known systematic effects (mostly instrumental, but including also the solar and earth-motion dipole, and the Zodiacal light). Sky maps are provided for the full Planck mission using all valid detectors in each frequency channel, and also for various subsets by splitting the mission in various time ranges or in subsets of the detectors in a given channel. These products are useful for the study of source variability, but they are especially interesting for characterisation purposes (see also the data validation section). The details of the start and end of the time ranges are given in this table.

To help in further processing, there are also masks of the Galactic Plane and of point sources, each provided for several different depths.

All sky maps are in Healpix format, with Nside of 2048, in Galactic coordinates, and Nested ordering. The signal is given in units of Kcmb for 30-353 GHz, and of MJy/sr (for a constant [math]\nu F_\nu[/math] energy distribution ) for 545 and 857 GHz. For each frequency channel, the intensity and polarization maps are packaged into a BINTABLE extension of a FITS file together with a hit-count map (or hit map, for short, giving the number of observation samples that are cumulated in a pixel, all detectors combined) and with the variance and covariance maps. Additional information is given in the FITS file header. The structure of the FITS file is given in the FITS file structure section below.


Production process[edit]

Sky maps are produced by combining appropriately the data of all working detectors in a frequency channel over some period of the mission. They give the best estimate of the signal from the sky (unpolarised) after removal, as far as possible, of known systematic effects and of the dipole signals induced by the motion of the solar system in the CMB and of the Planck satellite in the solar system. In particular, they include the Zodiacal light emission (Zodi for short) and also the scattering from the far-side lobes of the beams (FSL). More on this below.

HFI processing[edit]

The mapmaking and calibration process is described in detail in the Map-making section and in the mapmaking paper, where detailed references are found. In brief it consists of:

binning the TOI data onto rings 
Healpix rings (HPRs) are used here, each ring containing the combined data of one pointing period.
flux calibration 
at 100-353 GHz, the flux calibration factors are determined by correlating the signal with the orbital dipole, which is determined very accurately from the Planck satellite orbital parameters provided by Flight Dynamics. This provides a single gain factor per bolometer. At 545 and 857 GHz the gain is determined from the observation of Uranus and Neptune (but not Jupiter which is too bright) and comparison to recent models made explicitly for this mission. A single gain is applied to all rings at these frequencies.
destriping 
in order to remove low-frequency noise, an offset per ring is determined by minimizing the differences between HPRs at their crossings, and removed.
Zodiacal light correction 
a Zodiacal light model is used to build HPRs of the the Zodi emission, which is subtracted from the calibrated HPRs. (TBC)
projection onto the map 
the offset-corrected, flux-calibrated, and Zodi-cleaned HPRs are projected onto Healpix maps, with the data of each bolometer weighted by a factor of 1/NET of that bolometer.

These steps are followed by some post-processing which is designed to prepare the maps for the component separation work. This post processing consists of:

Dust bandpass leakage correction 
the Q and U maps are corrected for the dust leakage due to the different bandpasses that is determined using the ground method as described here
Far Side Lobe calibration correction 
the 100-217 maps are multiplied by factors of 1.00087, 1.00046, and 1.00043, respectively, to compensate for the non-removal of the far-side lobes, and similarly the corresponding covariance maps have also been corrected by multiplication by the square of the factor.
Fill missing pixels 
missing pixels are filled in with a value that is the mean of valid pixels within a given radius. A radius of 1 deg is used for the full channel maps, and 1.5 deg is used for the detset maps. This step is not applied to the single survey maps since they have large swaths of the sky that are not covered.

These maps provide the main mission products. Together with signal maps, hit count, variance, and variance maps are also produced. The hit maps give the (integer) number of valid TOI-level samples that contribute to the signal of each pixel. All valid samples are counted in the same way, i.e., there is no weighting factor applied. The variance maps project the white noise estimate, provided by the NETs, in the sky domain.

Note that the nominal mission maps have not had the post-processing applied, which makes them more easily comparable to the PR1 products.

LFI processing[edit]

LFI maps were constructed with the Madam map-making code, version 3.7.4. The code is based on generalized destriping technique, where the correlated noise component is modeled as a sequence of constant offset, called baselines. A noise filter was used to constrain the baseline solution allowing the use of 1 second baselines.

Radiometers were combined according to the horn-uniform weighting scheme to minimize systematics. The used weights are listed in Map-making. The flagged samples were excluded from the analysis by setting their weights to $C_{w}^{-1}$ = 0. The galaxy region was masked out in the destriping phase, to reduce error arising from strong signal gradients. The polarization component was included in the analysis...

A detailed description of the map-making procedure is given in Planck-2013-II[1] and in section Map-making.

Types of maps[edit]

Full mission, full channel maps (6 HFI, 3 LFI)[edit]

Full channel maps are built using all the valid detectors of a frequency channel and cover the either the full or the nominal mission. For HFI, the 143-8 and 545-3 bolometers are rejected entirely as they are seriously affected by RTS noise. For this release, HFI provides the Q and U components for the 353 GHz channel only. The maps are displayed in the figures below. The color range is set using a histogram equalisation scheme (from HEALPIX) that is useful for these non-Gaussian data fields.

Nominal mission, full channel maps (6 HFI, 3 LFI)[edit]

These maps are similar to the ones above, but cover the nominal mission only. They are meant primarily to be compared to the PR1 products in order to see the level of improvements in the processing. Because of this, they are produced in Temperature only, and have not had the post-processing applied.

Single survey, full channel maps (30 HFI, ??? LFI)[edit]

Single survey maps are built using all valid detectors of a frequency channel; they cover separately the different sky surveys. The surveys are defined as the times over which the satellite spin axis rotates but 180 degrees, which, due to the position of the detectors in the focal plane does not cover the full sky, but a fraction between ~80 and 90% depending on detector position. During adjacent surveys the sky is scanned in opposite directions. More precisely it is the ecliptic equator that is scanned in opposite directions. While these are useful to investigate variable sources, they are also used to study the systematics of the time-response of the detectors as they scan bright sources, like the Galactic Plane, in different directions during different survey. Note that the HFI and LFI missions cover 5 and ??? surveys, respectively, and in both cases the last survey in incomplete.

Year maps, full channel maps (12 HFI, 6 LFI)[edit]

These maps are built using the data of surveys 1+2, surveys 3+4, and so forth. They are used to study long-term systematic effects.

Half-mission maps, full channel maps (12 HFI, 6 LFI)[edit]

For HFI, the half mission is defined after eliminating those rings discarded for all bolometers. There are 347 such rings, may of which are during the 5th survey when the End-of-Life tests were performed. The remaining 26419 rings are divided in half (up to the odd ring) to define the two halves of the mission. This exercise is done for the full mission only.

Full mission, detector set or detector pairs maps (8 HFI, 8 FI)[edit]

The objective here is to build independent temperature and polarisation maps with the two pairs of polarised detectors of each channel where they are available, i.e. in the 30-353 GHz channels. The table below indicates which detectors were used to built each detector set (detset).

Definition of HFI Detector Sets
Frequency DetSet1 DetSet2
100 GHz 100-1a/b & 100-4a/b 100-2a/b & 100-3a/b
143 GHz 143-1a/b 1 & 43-3a/b 143-2a/b & 143-4a/b
217 GHz 217-5a/b & 217-7a/b 217-6a/b & 217-8a/b
353 GHz 353-3a/b & 353-5a/b 353-4a/b & 353-6a/b

Full mission, single detector maps (18 HFI)[edit]

These maps are built only for the HFI SWBs (non polarized) and contain only temperature data, of course.

Half-ring maps (64 HFI, ??? LFI)[edit]

These maps are similar to the ones above, but are built using only the first or the second half of each ring (or pointing period). The HFI provides half-ring maps for the full mission only, and for the full channel, the detsets, and the single bolometers. The LFI .....


Masks[edit]

Masks are provided of the Galactic Plane and of the point sources. For the Galactic Plane, eight masks are given covering different fractions of the sky, and for the points sources two masks are given, at the 5 and 10 sigma level, for each Planck HFI frequency channel. These are generic masks, specific masks applicable to other products are delivered with the products themselves.

The table below gives the ranges in terms of ESA pointing-ID, HFI ring number, and OD. The OD ranges are indicative only: they indicate that the given ring occurs during that OD.


Ranges for mission and surveys
Range ODs rings pointing-IDs Comment
nominal mission 91 - 563 240 - 14723 00004200 - 03180200
full mission 91 - 974 240 - 27005 00004200 - 05322620 for HFI
Survey 1 91 - 270 240 - 5720 00004200 - 01059820
Survey 2 270 - 456 5721 - 11194 01059830 - 02114520
Survey 3 456 - 636 11195 - 16691 02114530 - 03193660
Survey 4 636 - 807 16692 - 21720 03193670 - 04243900
Survey 5 807 - 974 21721 - 27005 05267180 - 05322590 end of mission for HFI
Survey 5 807 - 993 21721 - 27641 05267180 - 06344800 end of survey for LFI
Survey 6 993 - tbd 27642 - tbd 06344810 - tbd LFI only
HFI mission-half-1 91 - 531 240 - 13471 00004200 - 03155580
HFI mission-half-2 531 - 974 13472 - 27005 03155590 - 05322590

The Zodiacal light correction maps[edit]

The Zodiacal light signal depends on the location of the observer relative to the Zodiacal light bands, and thus it is not a fixed pattern on the sky but depends on the period of observation. The maps presented here are the difference between the uncorrected (and not delivered) and the corrected maps.


Caveats and known issues[edit]

TBW

Map zero-level[edit]

For the 100 to 857 GHz maps, the zero levels are set to their optimal levels for Galactic and CIB studies. A procedure for adjusting them to astrophysical values is given in the HFI Mapmaking and Calibration paper [2].

For the 30, 44 and 70 GHz, maps are corrected for zero level monopole by applying an offset correction, see LFI Calibration paper Planck-2013-V[3] section 3.4 "Setting the zero levels in the maps". Note that the offset applied is indicated in the header as a comment keyword.

Inputs[edit]

HFI inputs[edit]

  • The cleaned TOIs of signal of each detector, together with their flags, produced by the TOI processing pipeline
  • The TOIs of pointing (quaternions), described in Detector pointing
  • Bolometer-level characterization data, from the DPC's internal IMO (not distributed)
  • Planck orbit data used to compute and remove the earth dipole
  • WMAP solar dipole information used to calibrate the CMB channels
  • Planet models used to calibrate the Galactic channels.

LFI inputs[edit]

The Madam map-maker takes as an input:

  • The calibrated timelines (for details see TOI Processing)
  • The detector pointings (for details see Detector pointing)
  • The noise information in the form of three-parameter (white noise level ($\sigma$), slope, and knee frequency ($f_\mathrm{knee}$)) noise model (for details see RIMO)

Related products[edit]

Masks[edit]

Masks are provided of

the point sources
15 masks are provided, three for the LFI (one mask for each frequency masking at the 4[math]\sigma[/math] level) and 12 for the HFI (two masks for each frequency at the 5 and 10[math]\sigma[/math] levels. For the HFI the masks can be used as they are, for the LFI they need to be downgraded to Nside=1024 except for the 70 GHz channel at Nside=2048 which does not need to be downgraded.
the Galactic Plane
8 masks are provided giving 20, 40, 60, 70, 80, 90, 97, and 99% sky coverage in two different files, at Nside=2048. For the HFI they can be used as they are, for the LFI they need to be downgraded at Nside=1024 (note that if using the 70 GHZ at Nside=2048 no downgraded is needed)


The masks are binary, in GALACTIC coordinates, and NESTED ordering. The table below give the filenames.


FITS filenames for masks
Frequency LFI Point Source masks
30GHz LFI_MASK_030-ps_2048_R1.00.fits
44GHz LFI_MASK_044-ps_2048_R1.00.fits
70GHz LFI_MASK_070-ps_2048_R1.00.fits
HFI Point Source masks
HFI_Mask_PointSrc_2048_R1.10.fits
Galactic Plane masks
HFI_Mask_GalPlane_2048_R1.10.fits


The masks are shows below in a single figure. While this is quite clear for the Galactic Plane masks, it is less so for the point source masks, but it does give a clear perspective on how the latter are distributed over the sky.

File names[edit]

The FITS filenames are of the form {H|L}FI_SkyMap_fff{-tag}_Nside_R2.nn_{coverage}-{type}.fits, where fff are three digits to indicate the Planck frequency band, tag indicates the single detector or the detset, Nside is the Healpix Nside of the map, coverage indicates which part of the mission is covered (full, half mission, survey, year, ...) , and the optional type indicates the subset of input data used. The table below lists the products by type, with the appropriate unix wildcards that form the full filename.

FITS filenames
Coverage filename half-ring filename
Full chan, full mission HFI_SkyMap_???_2048_R2.??_full.fits HFI_SkyMap_???_2048_R2.??_full-ringhalf-?.fits
Full channel, nominal mission HFI_SkyMap_???_2048_R2.??_nominal.fits n/a
Full channel, single survey HFI_SkyMap_???_2048_R2.??_survey-?.fits n/a
Full channel, single year HFI_SkyMap_???_2048_R2.??_year-?.fits n/a
Full channel, half mission HFI_SkyMap_???_2048_R2.??_halfmission*-?.fits n/a
Det-set, full mission HFI_SkyMap_???-ds?_2048_R2.??_full.fits HFI_SkyMap_???-ds?_2048_R2.??_full-ringhalf-?.fits
Single SWB, full mission HFI_SkyMap_???-?_2048_R2.??_full.fits HFI_SkyMap_???-?_2048_R2.??_full-ringhalf-?.fits

For the benefit of users who are only looking for the frequency maps with no additional information, we also provide a file combining the 9 frequency maps as separate columns in a single extension. The 9 columns in this file contain the intensity maps ONLY and no other information (hit maps and variance maps) is provided.


FITS file structure[edit]

FITS file structure

The FITS files for the sky maps contain a minimal primary header with no data, and a BINTABLE extension (EXTENSION 1, EXTNAME = FREQ-MAP) containing the data. The structure is shows schematically in the figure at right.

The FREQ-MAP extension contains is a 3-column table that contain the signal, hit-count and variance maps, all in Healpix format, in columns 1, 2, and 3, respectively. The number of rows is 50331648 for HFI and LFI 70 GHz at Nside=2048 and 12582912 for LFI maps at Nside=1024 (N.B: Npix = 12 Nside^2). The three columns are I_STOKES for the intensity (or temperature) signal, HIT for the hit-count and II_COV for the variance. The exact order of the columns in the figure is indicative only, and the details can be found in the keywords.

Keywords indicate the coordinate system (GALACTIC), the Healpix ordering scheme (NESTED), the units (K_cmb or MJy/sr) of each column, and of course the frequency channel (FREQ). The COMMENT fields give a one-line summary of the product, and some other information useful for traceability within the DPCs. The original filename is also given in the FILENAME keyword as are the datasum and the md5 checksum for the extension. The BAD_DATA keyword gives the value used by Healpix to indicate pixels for which no signal is present (these will also have a hit-count value of 0). The COMMENT fields give further information including some traceability data for the DPC's. The main parameters are summarised below:


Sky map file data structure
1. EXTNAME = 'FREQ-MAP' : Data columns
Column Name Data Type Units Description
I_STOKES Real*4 K_cmb or MJy/sr The signal map
HITS Int*4 none The hit-count map
II_COV Real*4 K_cmb2 or (MJy/sr)2 The variance map
Keyword Data Type Value Description
PIXTYPE string HEALPIX
COORDSYS string GALACTIC Coordinate system
ORDERING string NESTED Healpix ordering
NSIDE Int 1024 or 2048 Healpix Nside
FIRSTPIX Int*4 0 First pixel number
LASTPIX Int*4 12582911 or 50331647 Last pixel number
FREQ string nnn The frequency channel


The same structure applies to all SkyMap products, independent of whether they are full channel, survey of half-ring. The distinction between the types of maps is present in the FITS filename (and in the traceability comment fields).

References[edit]

  1. Planck 2013 results. II. Low Frequency Instrument data processing, Planck Collaboration, 2014, A&A, 571, A2
  2. Planck 2013 results. V. LFI Calibration, Planck Collaboration, 2014, A&A, 571, A5

Flexible Image Transfer Specification

Cosmic Microwave background

(Planck) High Frequency Instrument

[LFI meaning]: absolute calibration refers to the 0th order calibration for each channel, 1 single number, while the relative calibration refers to the component of the calibration that varies pointing period by pointing period.

To be confirmed

Noise Equivalent Temperature

(Planck) Low Frequency Instrument

random telegraphic signal

European Space Agency

Operation Day definition is geometric visibility driven as it runs from the start of a DTCP (satellite Acquisition Of Signal) to the start of the next DTCP. Given the different ground stations and spacecraft will takes which station for how long, the OD duration varies but it is basically once a day.

Data Processing Center