Sky temperature maps
Introduction[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.
Sky maps are provided for the nominal Planck mission and for the first two single surveys, the third one being covered only for a small part during the nominal mission (REF). AMo: There is a table with table below that defines these coverage periods, but I believe that information should be in an earlier section that describes the mission and the events that interrupted it, the planet passages, the pointing, issues relating to timing, etc. That section should define a pointing period, and operational day, etc. There is some of that info in the HFI pre-processing section, but that may not be the best place for it.For characterization purposes, are also provided maps covering the nominal survey but using only half of the available data. These are the ringhalf_{1|2} maps, which are built using the first and second half of the stable pointing part of the data in each pointing period.
| Name | Ini_OD | Ini_Ring | Ini_ptgID | End_OD | End_ring | End_ptgID |
|---|---|---|---|---|---|---|
| Nominal | 91 | 240 | 00004200 | 563 | 14724 | 03180200 |
| HFI-Full | 91 | 240 | 00004200 | 993 | 27008 | 06344800 |
| LFI-Full | 91 | 240 | 00004200 | TBD | TBD | TBD |
| SCAN1 | 91 | 240 | 00004200 | 270 | 5720 | 01059820 |
| SCAN2 | 270 | 5721 | 01059830 | 456 | 11194 | 02114520 |
| SCAN3 | 456 | 11195 | 02114530 | 636 | 16691 | 03193660 |
| SCAN4 | 636 | 16692 | 03193670 | 807 | 21720 | 04243900 |
| SCAN5 | 807 | 21721 | 95000020 | 993 | 27008 | 06344800 |
| SCAN6 | 993 | ---- | 06344810 | 993 | ---- | TBD |
All sky maps are in Healpix format, with Nside of 2048 for HFI and of 1024 for LFI, in Galactic coordinates, and Nested ordering. The signal is given in units of Kcmb for 33-353 GHz, and of MJy/sr (for a constant $\nu F_\nu$ energy distribution ) for 545 and 857 GHz. Each sky map is packaged into a BINTABLE extension of a FITS file together with a hit-count map (or hit map, for short) and a variance map, and additional information is given in the FITS file header. The structure of the FITS file is given in the FITS file structure section below.
The FITS filenames are of the form {H|L}FI_SkyMap_fff_nnnn_R1.nn_{type}_{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, by their names, is given in the List of products below.
HFI processing[edit]
The inputs to the mapmaking are TOIs of signal that have been cleaned (as far as possible) of instrumental effects and calibrated in absorbed watts. While the processing involved is described in detail in the TOI processing section, we give a very brief summary here for convenience. That pipeline performs the following operations:
- demodulation
- this is performed around a variable level which is determined from the valid input data (a validity flag from a previous version of the processing is used for this purpose), and the data are converted to engineering units (V) using known conversion coefficients.
- despiking
- using the demodulated data converted to V (by the transfer function) the glitches are identified and fitted with templates. A glitch flag is produced that identifies the strongest part of the glitches, and a timeline of glitch tails is produced from the template fits, and subtracted from the demodulated timeline from step 1. Finally, the flagged ranges are replaced with data from an average over the pointing period (TBC)
- dark template removal
- the two dark bolometers are demodulated and despiked as above; the resulting timelines are then smoothed and used as an indicator of the overall temperature variations of the bolometer plate. Where the variations are consistent with each other, they are combined and removed from the bolometer signal timelines using appropriate coupling coefficients. The few percent of the data where they are not consistent are flagged on the timelines.
- conversion to absorbed power
- the timeline is converted to watts of absorbed power using the bolometer function. This includes a non-linearity correction
- removal of the 4K cooler lines
- the electromagnetic interference of the 4K cooler with the bolometer readout wires induces some sharp lines in the signal power spectra at frequencies of the 4K cooler's fundamental and its multiples, folded by the signal modulations. Fourier coefficients of the relevant lines are determined on a per-ring basis, and then removed from the data. The quality of the removal depends on the bolometer.
- deconvolution by the time transfer function
- this is done to correct for the non-instantaneous time response of the bolometers. The function itself is modeled using 4 parameters which are adjusted primarily on the planet data and also from comparisons of the northward and southward scans of the Galactic Plane. It is then removed using Fourier techniques, which has the side-effect of increasing the noise at high frequencies.
- jump correction
- removes some (relatively rare: 0.3 jumps per bolometer per pointing period, on average) jumps in the signal baseline. The jumps are detected characterized on smoothed TOIs, and corrected by adding a constant to part of the signal timeline. The origin of the jumps is not known.
The results of this processing are a timeline of signal (in absorbed watts) and a valid data flag timeline for each of the 50 valid bolometers processed; these timelines contain the full sky signal, i.e., including the solar and orbital dipoles, the Zodiacal light, and contributions from the Far-Side lobes. The dipoles are necessary for the flux calibration and are removed at the mapmaking stage. The remaining two bolometers (143-8 and 535-3) show semi-random jumps in the signal level, typically jumping over 2-5 different pseudo-baseline levels, a behavior known as Random Telegraphic Signal, so that these are commonly called the RTS bolometers. Finally, ring-level statistics of different types (mean, median, rms, kurtosis, etc.) are determined on a per-ring basis for all timelines, and a selection based on these statistics is used to discard anomalous rings, which are recorded in a ring-level flag for each valid bolometer timeline.
Throughout this processing, bright planets (Mars, Jupiter, Saturn, Uranus) and bright asteroids are masked in the timeline in order to avoid ringing effects in the processing. Since they move on the sky, the portion of the sky masked during one survey is observed during one, and no hole is left in the final map. In parallel, the planet data are processed in a similar way, but with different parameters for the despiking step, and without the final jump correction step. These results are processed separately to determine the beam shapes and the focal plane geometry.
The pointing is determined starting from the AHF produced by MOC, which gives the direction and orientation of the LOS of a fiducial position in the focal plane at frequencies of 8Hz during stable pointing and 4 Hz during maneuvers (TBC for details, reference). This is interpolated to the times of data observation (ref to method), corrected for the wobble and other time-dependent offsets determined from the observed positions of a large number of sources around the sky, and finally converted to the LOS of each detector using the quaternions in the IMO (which are determined from observations of bright planets - see the Focal plane reconstruction pipeline).
The mapmaking pipeline is described in detail in the Map-making section, and a brief summary is given here for convenience.
The cleaned TOIs of signal of each detector, together with their flags, produced by the TOI processing pipeline, and the TOIs of pointing (quaternions), described in Detectors pointing and beams, are the inputs to the mapmaking step.
The input signal TOIs are expressed in Watts from the sky absorbed by the bolometer, and their associated flags are used to samples or full rings to discard. Are discarded periods of unstable pointing and pointing maneuvers in general, glitched data, transits over bright planets (since they move, the hole flagged during one survey is covered during another sky survey), and some full rings are discarded if their noise properties differ significantly from the nominal value and the few rings of duration longer than 90 min, since the pointing is not sufficiently stable over such long periods (details in Discarded rings section).
The preparation of input pointing TOIs is described in Detectors pointing and beams. In brief, the STR (StarTracker) pointing produced by Flight Dynamics is interpolated to the detector sampling frequency in order to obtain a tuple of pointing quaternions for each sample and corrected for certain known effects. The angular offset between the STR line of sight and that of each bolometer is reflected in the Focal Plane Geometry, which is determined from the observation of bright planets. Also, the STR pointing timeline is corrected for slowly varying offsets between the STR and the HFI focal plane using observations of all planets and of other (fixed) bright sources.
Using the pointing TOIs, the signal TOIs are first used to build Healpix rings using the nearest grid point method; each ring containing the combined data of one pointing period. These are then calibrated in brightness, cleaned of the dipole signals, and projected onto Healpix maps as explained in the following sections.
The cleaned TOIs must be calibrated in astrophysical units. At 100-353 GHz, the flux calibration gains are determined for each pointing period (or ring) from the solar-motion dipole after removal of the small dipole induced by the motion of the Planck satellite in the solar system. The solar-motion dipole from WMAP (REF) is used for this purpose. This gain by ring is then smoothed with a window of width 50 rings, which reveals an apparent variation of ~1-2% on a scale of 100s to 1000s of rings for the 100-217 GHz channels, and is applied to the Watt data. At 353GHz, where the solar motion dipole is weaker compared to the signal, no gain variation is detected, and a single fixed gain is applied to all rings. At 545 and 857 GHz the gain is determined from the observation of Uranus and Neptune (Jupiter is not used because its brightness produced some non-linearity in the bolometer response) and comparison to recent models (REF) made explicitly for this mission. A single gain is applied to all rings at these frequencies.
Prior to projecting the Healpix rings (HPRs) onto a map, a destriping approach is used to remove low-frequency noise. The noise is modelled as the sum of a white noise component and a constant, or offset, per pointing period which represents the low frequency 1/f noise. The offsets are determined by minimizing the differences between HPRs at their crossings. After subtracting these offsets, calibrated data are projected onto Healpix maps, with the data of each bolometer weighted by a factor of 1/NET of that bolometer, and accounting for the slight different band transmission profiles of the bolometers in each band.
These maps provide the main mission products. A second, reduced, set of maps, cleaned of the Zodiacal emission of the FSL leakage is also produced for the nominal mission and the two single surveys, but not for the half-rings (since the contribution would be the same for the two halves of each ring). For this purpose, the the Zodiacal emission and the FSL contamination, which are not fixed on the sky, are modeled separately at HPR-level, and subtracted from the signal HPR before projecting them onto the maps.
Together with signal maps, hit count 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.
LFI processing[edit]
LFI processing is covered in Sect. 4.5
Selected images[edit]
Insert here some images:
Types of maps[edit]
Full channel maps[edit]
Full channel maps are built using all the valid detectors of a frequency channel and cover the full mission (or the nominal mission for the 1st release). For HFI, the 143-8 and 545-3 bolometers are rejected entirely as they are seriously affected by RTS noise.
Single survey maps[edit]
Single survey maps are built using all valid detectors of a frequency channel, but cover separately the different sky surveys. The single sky surveys are defined in terms of the direction of the satellite's spin axis: the first survey covers from the beginning of the science observations (the First Light Survey) to the time when the spin axis has rotated by 180 degrees (to the nearest pointing period), the following ones covers from 180 to 360, and so on. In the case of the nominal mission, the process stops at the third survey, which is incomplete. In the case of the full mission the 4th survey was interrupted shortly before completing the 180 degree rotation (see LINK), in order to begin observing with a different scanning law. The HFI mission ended slightly before the natural end of the 5th survey, the LFI mission continued to the XXX survey. The coverage of each of these periods in terms of ring number, pointingID, and OD, is given in the table below. Note that the OD numbers are only to indicate during which OD the period boundary occurs.
Half-ring maps[edit]
Half-ring maps are built using only the first or the second half of the stable pointing period data. There are thus two half-ring maps per frequency channel named ringhalf_1 and ringhalf_2 respectively. These maps are built for characterization purposes in order to perform null tests. In particular, the difference between the two half-ring maps at a given frequency give a good estimate of the high frequency noise in the data.
Caveats and known issues[edit]
The Zodiacal light and the Far-Side Lobes[edit]
Insert here how these are seen in the differences of the single survey maps
Artifacts near caustics of the scanning strategy[edit]
TBW if still an issue??
List of products[edit]
The list of products containing sky maps are given below, grouped by type
Outstanding: link to archive objects / LFI to fill in their products
- Full channel maps
LFI maps …. HFI_SkyMap_100_2048_R1.nn_nominal.fits HFI_SkyMap_143_2048_R1.nn_nominal.fits HFI_SkyMap_217_2048_R1.nn_nominal.fits HFI_SkyMap_353_2048_R1.nn_nominal.fits HFI_SkyMap_545_2048_R1.nn_nominal.fits HFI_SkyMap_857_2048_R1.nn_nominal.fits
- Single survey maps
LFI maps …. HFI_SkyMap_100_2048_R1.nn_survey_1.fits HFI_SkyMap_143_2048_R1.nn_survey_1.fits HFI_SkyMap_217_2048_R1.nn_survey_1.fits HFI_SkyMap_353_2048_R1.nn_survey_1.fits HFI_SkyMap_545_2048_R1.nn_survey_1.fits HFI_SkyMap_857_2048_R1.nn_survey_1.fits HFI_SkyMap_100_2048_R1.nn_survey_2.fits HFI_SkyMap_143_2048_R1.nn_survey_2.fits HFI_SkyMap_217_2048_R1.nn_survey_2.fits HFI_SkyMap_353_2048_R1.nn_survey_2.fits HFI_SkyMap_545_2048_R1.nn_survey_2.fits HFI_SkyMap_857_2048_R1.nn_survey_2.fits
- Half-ring maps
LFI maps …. HFI_SkyMap_100_2048_R1.nn_nominal_ringhalf_1.fits HFI_SkyMap_143_2048_R1.nn_nominal_ringhalf_1.fits HFI_SkyMap_217_2048_R1.nn_nominal_ringhalf_1.fits HFI_SkyMap_353_2048_R1.nn_nominal_ringhalf_1.fits HFI_SkyMap_545_2048_R1.nn_nominal_ringhalf_1.fits HFI_SkyMap_857_2048_R1.nn_nominal_ringhalf_1.fits HFI_SkyMap_100_2048_R1.nn_nominal_ringhalf_2.fits HFI_SkyMap_143_2048_R1.nn_nominal_ringhalf_2.fits HFI_SkyMap_217_2048_R1.nn_nominal_ringhalf_2.fits HFI_SkyMap_353_2048_R1.nn_nominal_ringhalf_2.fits HFI_SkyMap_545_2048_R1.nn_nominal_ringhalf_2.fits HFI_SkyMap_857_2048_R1.nn_nominal_ringhalf_2.fits
- Zodi and Far-side-lobes corrected maps
HFI_SkyMap_100_2048_R1.nn_nominal_ZodiCorrected.fits HFI_SkyMap_143_2048_R1.nn_nominal_ZodiCorrected.fits HFI_SkyMap_217_2048_R1.nn_nominal_ZodiCorrected.fits HFI_SkyMap_353_2048_R1.nn_nominal_ZodiCorrected.fits HFI_SkyMap_545_2048_R1.nn_nominal_ZodiCorrected.fits HFI_SkyMap_857_2048_R1.nn_nominal_ZodiCorrected.fits
HFI_SkyMap_100_2048_R1.nn_survey_1_ZodiCorrected.fits HFI_SkyMap_143_2048_R1.nn_survey_1_ZodiCorrected.fits HFI_SkyMap_217_2048_R1.nn_survey_1_ZodiCorrected.fits HFI_SkyMap_353_2048_R1.nn_survey_1_ZodiCorrected.fits HFI_SkyMap_545_2048_R1.nn_survey_1_ZodiCorrected.fits HFI_SkyMap_857_2048_R1.nn_survey_1_ZodiCorrected.fits HFI_SkyMap_100_2048_R1.nn_survey_2_ZodiCorrected.fits HFI_SkyMap_143_2048_R1.nn_survey_2_ZodiCorrected.fits HFI_SkyMap_217_2048_R1.nn_survey_2_ZodiCorrected.fits HFI_SkyMap_353_2048_R1.nn_survey_2_ZodiCorrected.fits HFI_SkyMap_545_2048_R1.nn_survey_2_ZodiCorrected.fits HFI_SkyMap_857_2048_R1.nn_survey_2_ZodiCorrected.fits
A comment from E. Keihänen:
Here is a list of things that should go into this section: Insert a table of maps delivered: *file name *radiometers included *PID/OD range *resolution *(-polarization included or not) *sky coverage *baseline length *-reference to input toi objects) Explain the format of the files, what is in what column, in what units. Information common for all LFImaps: *LFI maps were constructed with the Madam map-making code (version 3.7.4). Maps are in Healpix format, in nested pixeling scheme, in K_cmb units, and in galactic coordinate system. *Unobserved pixels are marked by the special value -1.6375e30.
EK's comment ends ------
FITS file structure[edit]
The FITS files for the sky maps contain a simple primary header with no data, and BINTABLE extension (EXTENSION 1, EXTNAME = 'FREQ-MAP') containing the data. The structure is shows schematically in the figure at right. The primary header has the form
;----------------------------------------------------------------------------- ; EXTENSION 0: ; - Header ;----------------------------------------------------------------------------- MRDFITS: Null image, NAXIS=0 SIMPLE = T /Dummy Created by MWRFITS v1.11 BITPIX = 8 /Dummy primary header created by MWRFITS NAXIS = 0 /No data is associated with this header EXTEND = T /Extensions may (will!) be present END
The FREQ-MAP BINTABLE extension contains the data. The table contains 3 columns of that contain the signal, variance, and hit-count maps in Healpix format. the number of rows is 50331648 for HFI and 12582912 for LFI, corresponding to the number of pixels in a Healpix map of Nside= 2048 and 1024, respectively (N.B: Npix = 12 Nside^2). The 3 columns are I_STOKES for the intensity (or temperature) signal, II_COV for the variance, and HIT for the hit-count. The exact order of the columns in the figure is indicative only, and the details can be found in the keywords. Keywords also 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 is 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).
A typical header for the data extension of an intensity only map is:
;----------------------------------------------------------------------------- ; EXTENSION 1: FREQ-MAP ; - Header ;----------------------------------------------------------------------------- MRDFITS: Binary table. 3 columns by 1 rows. XTENSION= 'BINTABLE' /Written by IDL: Thu Jan 31 11:03:21 2013 BITPIX = 8 / NAXIS = 2 /Binary table NAXIS1 = 603979776 /Number of bytes per row NAXIS2 = 1 /Number of rows PCOUNT = 0 /Random parameter count GCOUNT = 1 /Group count TFIELDS = 3 /Number of columns COMMENT COMMENT *** End of mandatory fields *** COMMENT EXTVER = 1 /Extension version DATE = '2013-01-31' /Creation date COMMENT COMMENT *** Column names *** COMMENT TTYPE1 = 'I_STOKES' / TTYPE2 = 'HITS ' / TTYPE3 = 'II_COV ' / COMMENT COMMENT *** Column formats *** COMMENT TFORM1 = '50331648E' / TFORM2 = '50331648J' / TFORM3 = '50331648E' / COMMENT COMMENT *** Column units *** COMMENT TUNIT1 = 'K_CMB ' / TUNIT2 = ' ' / TUNIT3 = 'K_CMB^2' / COMMENT COMMENT *** Planck params *** COMMENT EXTNAME = 'FREQ-MAP' / Extension name COORSYS = 'GALACTIC' / Coordinate system ORDERING= 'NESTED ' / Healpix ordering NSIDE = 2048 / Healpix Nside FIRSTPIX= 0 / First pixel # (0 based) LASTPIX = 50331647 / Last pixel # (0 based) FILENAME= 'HFI_SkyMap_217_2048_R1.10_nominal_ZodiCorrected.fits' / FITS filename CHECKSUM= '3aIB6Z993aGA3Y99' / HDU checksum created 2013-01-31T10:03:22 BAD_DATA= -1.63750E+30 / bad pixel value FREQ = '217 ' / reference frequency PROCVER = 'DX9_Delta' / Product version COMMENT COMMENT ------------------------------------------------------------------------ COMMENT Full channel sky map: nominal mission, corrected for Zodi & FSL COMMENT ------------------------------------------------------------------------ COMMENT Link to description in Planck Explanatory Supplement: COMMENT http://www.sciops.esa.int/wikiSI/planckpla/index.php?title= COMMENT Frequency_Maps&instance=Planck_PLA_ES COMMENT ------------------------------------------------------------------------ COMMENT HFI-DMC objects: COMMENT in-group: MAP_v53_noZodi_2048_GALACTIC_0240_27008/ COMMENT Creation date - object name COMMENT 13-01-03 18:33 - 217GHz_W_TauDeconv_nominal_I COMMENT 13-01-03 18:33 - 217GHz_W_TauDeconv_nominal_H COMMENT 13-01-03 18:33 - 217GHz_W_TauDeconv_nominal_II COMMENT ------------------------------------------------------------------------ END
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).
Cosmic Microwave background
(Planck) High Frequency Instrument
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.
(Planck) Low Frequency Instrument
To be defined / determined
Flexible Image Transfer Specification
To be confirmed
sudden change of the baseline level inside a ring
random telegraphic signal
Attitude History File
[ESA's] Mission Operation Center [Darmstadt, Germany]
Line Of Sight
Star TRacker
Noise Equivalent Temperature
Planck Legacy Archive
Explanatory Supplement
Data Management Component, the databases used at the HFI and LFI DPCs
