Difference between revisions of "Effective Beams"

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<span style="color:red">The second part of this section is mostly unreadable. Please use proper style in terms of sectioning (i.e. pseudo headings that are underlined), lists (bullet or numbered) - see other pages for examples.  Info regarding M3 (and NERCS) is probably irrelevant to external users)</span>
+
{{DISPLAYTITLE:2015 Effective Beams}}
 +
<span style="color:red"></span>
  
 
==Product description==
 
==Product description==
−
----------------------
 
−
 
 
The '''effective beam''' is the average of all scanning beams pointing at a certain direction within a given pixel of the sky map for a given scan strategy. It takes into account the coupling between azimuthal asymmetry of the beam and the uneven distribution of scanning angles across the sky.
 
The '''effective beam''' is the average of all scanning beams pointing at a certain direction within a given pixel of the sky map for a given scan strategy. It takes into account the coupling between azimuthal asymmetry of the beam and the uneven distribution of scanning angles across the sky.
−
It captures the complete information about the difference between the true and observed image of the sky. They are, by definition, the objects whose convolution with the true CMB sky produce the observed sky map.  
+
It captures the complete information about the difference between the true and observed image of the sky. The effective beams are, by definition, the objects whose convolution with the true CMB sky produce the observed sky map.  
  
−
The effective beam is computed by stacking within a small field around each pixel of the HEALPix sky map.  Due to the particular features of Planck scanning strategy coupled to the beam asymmetries in the focal plane, and data processing of the bolometer and radiometer TOIs, the resulting Planck effective beams vary over the sky.  
+
Details of the beam processing are given in the respective pages for [[Beams|HFI]] and [[Beams_LFI|LFI]].
  
−
----
+
The full algebra involving the effective beams for temperature and polarisation was presented in  {{BibCite|mitra2010}}, and a discussion of its application to Planck data is given in the appropriate LFI {{PlanckPapers|planck2013-p02d}}, {{PlanckPapers|planck2014-a05||Planck-2015-A05}} and HFI {{PlanckPapers|planck2013-p03c}} papers. Relevant details of the processing steps are given in the [[Beams|Effective Beams]] section of this document.
  
−
# '''Comparison of the images of compact sources observed by Planck-HFI with the results of FEBeCoP'''
+
<!-- Everything from here down to the "Production Process" section should eventually be moved to a new section the Joint Processing pages -->
  
−
 
+
===Comparison of the images of compact sources observed by Planck with FEBeCoP products===
−
We show here a comparison of the FEBeCoP derived effective beams, and associated point spread functions (see here), to the actual images of a few compact sources observed by Planck, for 30GHz and 100GHz frequency channels. We show below a few panels of source images organized as follows:
+
We show here a comparison of the FEBeCoP-derived effective beams, and associated point spread functions, PSF (the transpose of the beam matrix), to the actual images of a few compact sources observed by Planck, for all LFI and HFI  frequency channels, as an example. We show below a few panels of source images organized as follows:
 
* Row #1- DX9 images of four ERCSC objects with their galactic (l,b) coordinates shown under the color bar
 
* Row #1- DX9 images of four ERCSC objects with their galactic (l,b) coordinates shown under the color bar
−
* Row #2- linear scale FEBeCoP PSFs computed using input scanning beams BS Mars12 apodized for the CMB channels and the BS Mars12 for the sub-mm channels
+
* Row #2- linear scale FEBeCoP PSFs computed using input scanning beams, Grasp Beams, GB, for LFI and B-Spline beams,BS, Mars12 apodized for the CMB channels and the BS Mars12 for the sub-mm channels, for HFI (see section Inputs below).
 
* Row #3- log scale of #2; PSF iso-contours shown in solid line, elliptical Gaussian fit iso-contours shown in broken line
 
* Row #3- log scale of #2; PSF iso-contours shown in solid line, elliptical Gaussian fit iso-contours shown in broken line
 +
 +
<center>
 +
 +
<gallery widths=400px heights=400px perrow=2 caption="Comparison  images of compact sources and effective beams, PSFs">
 +
File:30.png| '''30GHz'''
 +
File:44.png| '''44GHz'''
 +
File:70.png| '''70GHz'''
 +
File:100.png| '''100GHz'''
 +
File:143.png| '''143GHz'''
 +
File:217.png| '''217GHz'''
 +
File:353.png| '''353GHz'''
 +
File:545.png| '''545GHz'''
 +
File:857.png| '''857GHz'''
 +
</gallery>
 +
</center>
 +
 +
===Histograms of the effective beam parameters===
 +
Here we present histograms of the three fit parameters - beam FWHM, ellipticity, and orientation with respect to the local meridian and of the beam solid angle. The sky is sampled (pretty sparsely) at 3072 directions which were chosen as HEALpix nside=16 pixel centers for HFI and at 768 directions which were chosen as HEALpix nside=8 pixel centers for LFI.  These uniformly sample the sky.
 +
 +
Where beam solid angle is estimated according to the definition:  '''<math> 4 \pi \sum</math>(effbeam)/max(effbeam)'''
 +
i.e., <math> 4 \pi \sum(B_{ij}) /  max(B_{ij}) </math>
  
  
 +
[[File:ist_GB.png | 800px| thumb | center| '''Histograms for LFI effective beam parameters''' ]]
 +
[[File:ist_BS_Mars12.png | 800px| thumb | center| '''Histograms for HFI effective beam parameters''' ]]
  
−
*'''30  GHz and 100 GHz'''
+
===Sky variation of effective beams solid angle and ellipticity of the best-fit Gaussian===
 +
* The discontinuities at the Healpix domain edges in the maps are a visual artifact due to the interplay of the discretized effective beam and the Healpix pixel grid.
  
−
||border=1, width=1200, align=center
 
−
|| '''30 GHz''' || || '''100 GHz''' ||
 
−
|| %width=600px,%[[Attach:30.png|Attach:30.png]] || || %width=600px,%[[Attach:100.png|Attach:100.png]] ||
 
  
 +
<gallery widths=300px heights=220px perrow=3 caption="Sky variation of effective beams ellipticity of the best-fit Gaussian">
 +
File:e_030_GB.png| '''ellipticity - 30GHz'''
 +
File:e_044_GB.png| '''ellipticity - 44GHz'''
 +
File:e_070_GB.png| '''ellipticity - 70GHz'''
 +
File:e_100_BS_Mars12.png| '''ellipticity - 100GHz'''
 +
File:e_143_BS_Mars12.png| '''ellipticity - 143GHz'''
 +
File:e_217_BS_Mars12.png| '''ellipticity - 217GHz'''
 +
File:e_353_BS_Mars12.png| '''ellipticity - 353GHz'''
 +
File:e_545_BS_Mars12.png| '''ellipticity - 545GHz'''
 +
File:e_857_BS_Mars12.png| '''ellipticity - 857GHz'''
 +
</gallery>
  
−
[[File:30.png | 500px| thumb | center|  "'30GHz''']]
 
  
−
[[File:100.png | 500px| thumb | center | "'100GHz''' ]]
+
<gallery widths=300px heights=220px perrow=3 caption="Sky (relative) variation of effective beams solid angle of the best-fit Gaussian">
 +
File:solidarc_030_GB.png| '''beam solid angle (relative) variations wrt scanning beam - 30GHz'''
 +
File:solidarc_044_GB.png| '''beam solid angle (relative) variations wrt scanning beam - 44GHz'''
 +
File:solidarc_070_GB.png| '''beam solid angle (relative) variations wrt scanning beam - 70GHz'''
 +
File:solidarc_100_BS_Mars12.png| '''beam solid angle (relative) variations wrt scanning beam - 100GHz'''
 +
File:solidarc_143_BS_Mars12.png| '''beam solid angle (relative) variations wrt scanning beam - 143GHz'''
 +
File:solidarc_217_BS_Mars12.png| '''beam solid angle (relative) variations wrt scanning beam - 217GHz'''
 +
File:solidarc_353_BS_Mars12.png| '''beam solid angle (relative) variations wrt scanning beam - 353GHz'''
 +
File:solidarc_545_BS_Mars12.png| '''beam solid angle (relative) variations wrt scanning beam - 545GHz'''
 +
File:solidarc_857_BS_Mars12.png| '''beam solid angle (relative) variations wrt scanning beam - 857GHz'''
 +
</gallery>
  
  
−
----
+
<gallery widths=300px heights=220px perrow=3 caption="Sky (relative) variation of effective beams fwhm of the best-fit Gaussian">
 +
File:fwhm_030_GB.png| '''fwhm (relative) variations wrt scanning beam - 30GHz'''
 +
File:fwhm_044_GB.png| '''fwhm (relative) variations wrt scanning beam - 44GHz'''
 +
File:fwhm_070_GB.png| '''fwhm (relative) variations wrt scanning beam - 70GHz'''
 +
File:fwhm_100_BS_Mars12.png| '''fwhm (relative) variations wrt scanning beam - 100GHz'''
 +
File:fwhm_143_BS_Mars12.png| '''fwhm (relative) variations wrt scanning beam - 143GHz'''
 +
File:fwhm_217_BS_Mars12.png| '''fwhm (relative) variations wrt scanning beam - 217GHz'''
 +
File:fwhm_353_BS_Mars12.png| '''fwhm (relative) variations wrt scanning beam - 353GHz'''
 +
File:fwhm_545_BS_Mars12.png| '''fwhm (relative) variations wrt scanning beam - 545GHz'''
 +
File:fwhm_857_BS_Mars12.png| '''fwhm (relative) variations wrt scanning beam - 857GHz'''
 +
</gallery>
  
−
# '''Statistics of the effective beams computed using FEBeCoP for 100-857 GHz channels'''
 
  
−
We tabulate the simple statistics of FWHM, ellipticity, orientation and beam solid angle for a sample of 3072 directions.
+
<gallery widths=300px heights=220px perrow=3 caption="Sky variation of effective beams <math>\psi</math> angle of the best-fit Gaussian">
−
Statistics shown in the Table are derived from the histograms shown below.
+
File:psi_030_GB.png| '''<math>\psi</math> - 30GHz'''
 +
File:psi_044_GB.png| '''<math>\psi</math> - 44GHz'''
 +
File:psi_070_GB.png| '''<math>\psi</math> - 70GHz'''
 +
File:psi_100_BS_Mars12.png| '''<math>\psi</math> - 100GHz'''
 +
File:psi_143_BS_Mars12.png| '''<math>\psi</math> - 143GHz'''
 +
File:psi_217_BS_Mars12.png| '''<math>\psi</math> - 217GHz'''
 +
File:psi_353_BS_Mars12.png| '''<math>\psi</math> - 353GHz'''
 +
File:psi_545_BS_Mars12.png| '''<math>\psi</math> - 545GHz'''
 +
File:psi_857_BS_Mars12.png| '''<math>\psi</math> - 857GHz'''
 +
</gallery>
  
−
+
<!--
−
* The results/table for delivery for the Cosmo-channels (100 to 353GHz) were obtained with the v53 '''BS Mars12_apodized''' beam maps recently provided.
+
<gallery widths=500px heights=500px perrow=2 caption="Sky variation of effective beams solid angle and ellipticity of the best-fit Gaussian">
−
* We also provide the beam derived parameters for GH Mars12 for the cosmology channels (which do not suffer from convergence issues).
+
File:e_030_GB.png| '''ellipticity - 30GHz'''
 +
File:solidarc_030_GB.png| '''beam solid angle (relative variations wrt scanning beam - 30GHz'''
 +
File:e_100_BS_Mars12.png| '''ellipticity - 100GHz'''
 +
File:solidarc_100_BS_Mars12.png| '''beam solid angle (relative variations wrt scanning beam - 100GHz'''
 +
</gallery>
 +
-->
 +
 
 +
===Statistics of the effective beams computed using FEBeCoP===
 +
 
 +
We tabulate the simple statistics of FWHM, ellipticity (e), orientation (<math> \psi</math>) and beam solid angle, (<math> \Omega </math>), for a sample of 3072 and 768 directions on the sky for HFI and LFI data respectively. Statistics shown in the Table are derived from the histograms shown above.
 +
 
 +
* The derived beam parameters are representative of the DPC NSIDE 1024 and 2048 healpix maps (they include the pixel window function).
 +
* The reported FWHM_eff are derived from the beam solid angles, under a Gaussian approximation. These are best used for flux determination while the  the Gaussian fits to the effective beam maps are more suited for source identification.
  
  
Line 49: Line 119:
 
|+ '''Statistics of the FEBeCoP Effective Beams Computed with the BS Mars12 apodized for the CMB channels and oversampled'''
 
|+ '''Statistics of the FEBeCoP Effective Beams Computed with the BS Mars12 apodized for the CMB channels and oversampled'''
 
|-
 
|-
−
!  '''frequency'''  ||  '''mean(fwhm)''' [arcmin]  ||  '''sd(fwhm)''' [arcmin]  || '''mean(e)'''  ||  '''sd(e)'''  ||  '''mean(psi)''' [degree]  ||  '''sd(psi)''' [degree]  || '''mean(Solid Angle)''' [arcmin<math>^{2}</math>']  ||  '''sd(Solid Angle)''' [arcmin<math>^{2}</math>']
+
!  '''frequency'''  ||  '''mean(fwhm)''' [arcmin]  ||  '''sd(fwhm)''' [arcmin]  || '''mean(e)'''  ||  '''sd(e)'''  ||  '''mean(<math> \psi</math>)''' [degree]  ||  '''sd(<math> \psi</math>)''' [degree]  || '''mean(<math> \Omega </math>)''' [arcmin<math>^{2}</math>]  ||  '''sd(<math> \Omega </math>)''' [arcmin<math>^{2}</math>] || '''FWHM_eff''' [arcmin]  
 +
|-
 +
| 030 || 32.239 || 0.013 || 1.320 || 0.031 || -0.304 || 55.349 || 1189.513 || 0.842 || 32.34
 
|-
 
|-
−
| 100 || 9.651 || 0.014 || 1.186 || 0.023 || -0.024 || 55.400 || 105.778 || 0.311
+
| 044 || 27.005 || 0.552 || 1.034 || 0.033 || 0.059 || 53.767 || 832.946 || 31.774  || 27.12
 
|-
 
|-
−
| 143 || 7.248 || 0.015 || 1.036 || 0.009 || 0.383  || 54.130 || 59.954 || 0.246
+
| 070 || 13.252 || 0.033 || 1.223 || 0.026 || 0.587 || 55.066 || 200.742 || 1.027  || 13.31
 
|-
 
|-
−
| 217 || 4.990 || 0.025 || 1.177 || 0.030 || 0.836  || 54.999 || 28.447 || 0.271
+
| 100 || 9.651 || 0.014 || 1.186 || 0.023 || -0.024 || 55.400 || 105.778 || 0.311 || 9.66
 
|-
 
|-
−
| 353 || 4.818 || 0.024 || 1.147 || 0.028 || 0.655  || 54.745 || 26.714 || 0.250  
+
| 143 || 7.248 || 0.015 || 1.036 || 0.009 || 0.383  || 54.130 || 59.954 || 0.246  || 7.27
 +
|-
 +
| 217 || 4.990 || 0.025 || 1.177 || 0.030 || 0.836  || 54.999 || 28.447 || 0.271  || 5.01
 +
|-
 +
| 353 || 4.818 || 0.024 || 1.147 || 0.028 || 0.655  || 54.745 || 26.714 || 0.250 || 4.86
 
|-  
 
|-  
−
| 545 || 4.682 || 0.044 || 1.161 || 0.036 || 0.544  || 54.876 || 26.535 || 0.339  
+
| 545 || 4.682 || 0.044 || 1.161 || 0.036 || 0.544  || 54.876 || 26.535 || 0.339 || 4.84
 
|-
 
|-
−
| 857 || 4.325 || 0.055 || 1.393 || 0.076 || 0.876  || 54.779 || 24.244 || 0.193  
+
| 857 || 4.325 || 0.055 || 1.393 || 0.076 || 0.876  || 54.779 || 24.244 || 0.193 || 4.63
 
|}
 
|}
−
 
  
 
   
 
   
−
----
 
−
# '''FEBeCoP deliverables'''
 
  
−
* The derived beam parameters are representative of the DPC NSIDE 2048 healpix maps (they include the pixel window function).
 
−
* The reported FHWM are derived from the solid angles, under a Gaussian approximation.  The value in the values in parenthesis are the Gaussian fits to the effective beam maps.  The former is best used for flux determination, the latter for source identification.
 
  
−
{|border="1" cellpadding="5" cellspacing="0" align="center" style="text-align:center"
+
====Beam solid angles for the PCCS====
−
|+ '''Band averaged beam solid angles'''
 
−
|-
 
−
| '''Band'''  ||  '''Omega_beam''' [arcmin<math>^{2}</math>]  ||  '''Monte Carlo error'''[arcmin<math>^{2}</math>^]  || '''spatial variation''' [arcmin<math>^{2}</math>]  ||  '''bias''' [arcmin<math>^{2}</math>]  || '''FWHM_eff''' (Gaussian fit) [arcmin]
 
−
|-
 
−
| 100 || 105.78 || --- || 0.31 || --- || 9.66 (9.65)
 
−
|-
 
−
| 143 || 59.95 || --- || 0.25 || --- || 7.27 (7.25)
 
−
|-
 
−
| 217 || 28.45 || --- || 0.27 || --- || 5.01 (4.99)
 
−
|-
 
−
| 353 || 26.71 || --- || 0.25 || --- || 4.86 (4.82)
 
−
|-
 
−
| 545 || 26.54 || --- || 0.34 || --- || 4.84 (4.68)
 
−
|-
 
−
| 857 || 24.24 || --- || 0.19 || --- || 4.63 (4.33)
 
−
|}
 
  
−
----
+
*  <math>\Omega_{eff}</math> - is the mean beam solid angle of the effective beam, where beam solid angle is estimated according to the definition:  '''<math>4 \pi \sum </math>(effbeam)/max(effbeam)''', i.e. as an integral over the full extent of the effective beam, i.e. <math> 4 \pi \sum(B_{ij}) /  max(B_{ij}) </math>.
  
−
# '''Beam solid angles for the PCCS'''
+
* from <math>\Omega_{eff}</math> we estimate the <math>fwhm_{eff}</math>, under a Gaussian approximation - these are tabulated above
−
* Omega_beam - is the mean beam solid angle of the effective beam, where beam solid angle is estimated according to the definition:  4pi/sum(effbeam)/max(effbeam), i.e. as an integral over the full extent of the effective beam
+
** <math>\Omega^{(1)}_{eff}</math> is the beam solid angle estimated up to a radius equal to one <math>fwhm_{eff}</math> and <math>\Omega^{(2)}_{eff}</math> up to a radius equal to twice the <math>fwhm_{eff}</math>.
−
* from Omega_beam we estimate the fwhm_eff, under a Gaussian approximation - these are tabulated above
+
*** These were estimated according to the procedure followed in the aperture photometry code for the PCCS: if the pixel centre does not lie within the given radius it is not included (so inclusive=0 in query disc).
−
* Omega_beam_1 is the beam solid angle estimated up to a radius equal to 1xfwhm_eff and Omega_beam_2 up to a radius equal to 2xfwhm_eff
 
−
** These were estimated according to the procedure followed in the aperture photometry code for the PCCS: if the pixel centre does not lie within the given radius it is not included (so inclusive=0 in query disc).
 
  
  
 
{|border="1" cellpadding="5" cellspacing="0" align="center" style="text-align:center"
 
{|border="1" cellpadding="5" cellspacing="0" align="center" style="text-align:center"
 
|+'''Band averaged beam solid angles'''
 
|+'''Band averaged beam solid angles'''
−
|  '''Band'''  ||  '''Omega_beam'''[arcmin<math>^{2}</math>] || '''spatial variation''' [arcmin<math>^{2}</math>] ||  '''Omega_beam_1''' [arcmin<math>^{2}</math>]|| '''spatial variation-1''' [arcmin<math>^{2}</math>] ||  '''Omega_beam_2''' [arcmin<math>^{2}</math>] || '''spatial variation-2''' [arcmin<math>^{2}</math>]  
+
|  '''Band'''  ||  '''<math>\Omega_{eff}</math>'''[arcmin<math>^{2}</math>] || '''spatial variation''' [arcmin<math>^{2}</math>] ||  '''<math>\Omega^{(1)}_{eff}</math>''' [arcmin<math>^{2}</math>]|| '''spatial variation-1''' [arcmin<math>^{2}</math>] ||  '''<math>\Omega^{(2)}_{eff}</math>''' [arcmin<math>^{2}</math>] || '''spatial variation-2''' [arcmin<math>^{2}</math>]  
 +
|-
 +
|30 || 1189.513 || 0.842 || 1116.494 || 2.274 || 1188.945 || 0.847
 +
|-
 +
| 44 || 832.946 || 31.774 || 758.684 || 29.701 || 832.168 || 31.811
 +
|-
 +
| 70 || 200.742 || 1.027 || 186.260 || 2.300 || 200.591 || 1.027
 
|-
 
|-
 
| 100 || 105.778 || 0.311 || 100.830 || 0.410 || 105.777 || 0.311  
 
| 100 || 105.778 || 0.311 || 100.830 || 0.410 || 105.777 || 0.311  
Line 115: Line 174:
 
| 857 || 24.244 || 0.193 || 22.646 || 0.263 || 23.985 || 0.191  
 
| 857 || 24.244 || 0.193 || 22.646 || 0.263 || 23.985 || 0.191  
 
|}
 
|}
−
 
−
 
−
 
−
 
−
 
  
 
==Production process==
 
==Production process==
−
------------------------
+
FEBeCoP, or Fast Effective Beam Convolution in Pixel space{{BibCite|mitra2010}}, is an approach to representing and computing effective beams (including both intrinsic beam shapes and the effects of scanning) that comprises the following steps:
−
 
 
−
 
 
−
The methodology for computing effective beams for a scanning CMB experiment like Planck
 
−
was presented in our [[http://arxiv.org/pdf/1005.1929 | paper]].
 
−
 
 
−
FEBeCoP, or Fast Effective Beam Convolution in Pixel space, is an approach to representing and computing effective beams (including both intrinsic beam shapes and the effects of scanning) that comprises the following steps:
 
 
* identify the individual detectors' instantaneous optical response function (presently we use elliptical Gaussian fits of Planck beams from observations of planets; eventually, an arbitrary mathematical representation of the beam can be used on input)
 
* identify the individual detectors' instantaneous optical response function (presently we use elliptical Gaussian fits of Planck beams from observations of planets; eventually, an arbitrary mathematical representation of the beam can be used on input)
 
* follow exactly the Planck scanning, and project the intrinsic beam on the sky at each actual sampling position
 
* follow exactly the Planck scanning, and project the intrinsic beam on the sky at each actual sampling position
Line 137: Line 185:
  
  
 +
Computation of the effective beams at each pixel for every detector is a challenging task for high resolution experiments. FEBeCoP is an efficient algorithm and implementation which enabled us to compute the pixel based effective beams using moderate computational resources. The algorithm used different mathematical and computational techniques to bring down the computation cost to a practical level, whereby several estimations of the effective beams were possible for all Planck detectors for different scan and beam models, as well as different lengths of datasets.
  
−
==Inputs==
 
−
------------
 
  
−
In order to fix the convention of presentation of the scanning and effective beams, we show the classic view of the Planck focal plane as seen by the incoming CMB photon. The scan direction is marked, and the toward the center of the focal plane is at the 85 deg angle w.r.t spin axis pointing upward in the picture.  
+
===Pixel Ordered Detector Angles (PODA)===
 +
The main challenge in computing the effective beams is to go through the trillion samples, which gets severely limited by I/O. In the first stage, for a given dataset, ordered lists of pointing angles for each pixel - the Pixel Ordered Detector Angles (PODA) are made. This is an one-time process for each dataset. We used computers with large memory and used tedious memory management bookkeeping to make this step efficient.
  
 +
===effBeam===
 +
The effBeam part makes use of the precomputed PODA and unsynchronized reading from the disk to compute the beam. Here we tried to made sure that no repetition occurs in evaluating a trigonometric quantity.
  
−
[[File:PlanckFocalPlane.png | 500px| thumb | center|  "'Planck Focal Plane''']]
 
  
 +
One important reason for separating the two steps is that they use different schemes of parallel computing. The PODA part requires parallelisation over time-order-data samples, while the  effBeam part requires distribution of pixels among different computers.
  
  
−
<span style="color:Red">A list (and brief description to the extent possible) of the input data used to generate this product (down to file names), as well as any external ancillary data sets which were used.</span>
+
===Computational Cost===
 +
The computation of the effective beams has been performed at the NERSC Supercomputing Center. The table below shows the computation cost for FEBeCoP processing of the nominal mission.
  
−
# Detector pointings:
+
{|border="1" cellpadding="5" cellspacing="0" align="center" style="text-align:center"
−
# Intrinsic beam description:
+
|+ '''Computational cost for PODA, Effective Beam and  single map convolution. Wall-clock time is given as a guide, as found on the NERSC supercomputers.'''
−
# Beam cutoff radius: 2.25 times geometric mean of FWHM of all detectors in a channel
+
|-
−
# map resolution for the derived beam data object:
+
|Channel ||030 || 044 || 070 || 100 || 143 || 217 || 353 || 545 || 857
−
* N'_side_' = 1024 for 100GHz
+
|-
−
* N'_side_' = 2048 for all other frequencies
+
|PODA/Detector Computation time (CPU hrs) || 85 || 100  || 250 || 500 || 500 || 500 || 500 || 500 || 500
 +
|-
 +
|PODA/Detector Computation time (wall clock hrs) || 7 || 10  || 20 || 20 || 20 || 20 || 20 || 20 || 20
 +
|-
 +
|Beam/Channel Computation time (CPU hrs) || 900 || 2000 || 2300 || 2800 ||  3800 || 3200 || 3000 || 900 || 1100
 +
|-
 +
|Beam/Channel Computation time (wall clock hrs) || 0.5 || 0.8  || 1 || 1.5 || 2 || 1.2 || 1 || 0.5 || 0.5
 +
|-
 +
|Convolution Computation time (CPU hr) || 1 || 1.2 || 1.3 || 3.6 || 4.8 || 4.0 || 4.1 || 4.1 || 3.7
 +
|-
 +
|Convolution Computation time (wall clock sec) || 1 || 1 || 1 || 4 || 4 || 4 || 4 || 4 || 4
 +
|-
 +
|Effective Beam Size (GB) || 173 || 123 || 28 || 187 || 182 || 146 || 132 || 139 || 124
 +
|}
  
  
−
==Related products==
+
The computation cost, especially for PODA and Convolution, is heavily limited by the I/O capacity of the disc and so it depends on the overall usage of the cluster done by other users.
−
<span style="color:Red">A description of other products that are related and share some commonalities with the product being described here. E.g. if the description is of a generic product (e.g. frequency maps), all the products falling into that type should be listed and referenced.</span>
 
  
−
Effective beams are located at nersc:
+
==Inputs==
−
??
+
In order to fix the convention of presentation of the scanning and effective beams, we show the classic view of the Planck focal plane as seen by the incoming CMB photon. The scan direction is marked, and the toward the center of the focal plane is at the 85 deg angle w.r.t spin axis pointing upward in the picture.
−
 
−
and in both the HFI and LFI DPCs at:
 
−
* On disk: /space/SimuData/effBeam_HFI_v41
 
−
* DMC group: /data/dmc/MISS01/DATA/FEBeCoP_v41
 
  
−
Interface modules were developed to easily access the beams and the PSFs from the disk and the database.
 
−
For HFI:
 
−
The codes for reading the beams/PSFs and demonstration programs  (http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/)
 
−
FOr LFI:
 
  
 +
[[File:PlanckFocalPlane.png | 500px| thumb | center|'''Planck Focal Plane''']]
  
−
The interface contains Fortran 90 routines to read the beams either from disk or from database. There are IDL routines also to read the beams from disk with detailed inbuilt help and fast examples.
 
  
−
There are two sets of (serial) demonstration programs:
+
===The Focal Plane DataBase (FPDB)===
 +
The FPDB contains information on each detector, e.g., the orientation of the polarisation axis, different weight factors, (see the instrument [[The RIMO|RIMOs]]):
  
−
* to extract beams/PSF at any given set of pixels from disk/database and make .fits skymaps
+
*HFI - {{PLASingleFile|fileType=rimo|name=HFI_RIMO_R1.00.fits|link=The HFI RIMO}}
−
** beam_extract_f : extract beams from disk
+
*LFI - {{PLASingleFile|fileType=rimo|name=LFI_RIMO_R1.12.fits|link=The LFI RIMO}}
−
** beam_extract_f_PIO: extract beams from database
 
−
** psf_extract_f  : extract PSF from disk
 
−
** psf_extract_f_PIO : extract PSF from database
 
  
−
* to make a full sky convolution of input maps with effective beams
 
−
** effConv : convolve map reading beam from disk
 
−
** effConv_PIO : convolve map reading beam from database
 
  
 +
<!--
 +
*HFI - LFI_RIMO_DX9_PTCOR6 -  {{PLASingleFile|fileType=rimo|name=HFI_RIMO_R1.00.fits|link=The HFI RIMO}}
 +
*LFI - HFI-RIMO-3_16_detilt_t2_ptcor6.fits - {{PLASingleFile|fileType=rimo|name=LFI_RIMO_R1.12.fits|link=The LFI RIMO}}
  
−
Example parameter files (with explanation) for these demonstration programs are available here: http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/params/
+
{{PLADoc|fileType=rimo|link=The Plank RIMOS}}
 +
-->
  
−
A detailed README on the usage of the routines and the programs are available as: http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/README.txt
+
===The scanning strategy===
−
included here:
+
The scanning strategy, the three pointing angle for each detector for each sample: Detector pointings for the nominal mission covers about 15 months of observation from Operational Day (OD) 91 to OD 563 covering 3 surveys and half.
  
−
*HFI
+
===The scanbeam===
 +
The scanbeam modeled for each detector through the observation of planets. Which was assumed to be constant over the whole mission, though FEBeCoP could be used for a few sets of scanbeams too.
  
−
How to use FEBeCoP effective beams and PSFs on magiqueIII
+
* LFI: [[Beams LFI#Main beams and Focalplane calibration|GRASP scanning beam]] - the scanning beams used are based on Radio Frequency Tuned Model (RFTM) smeared to simulate the in-flight optical response.
−
---------------------------------------------------
+
* HFI: [[Beams#Scanning beams|B-Spline, BS]] based on 2 observations of Mars.
  
−
<span style="color:red">Is this of any relevance?  external users don't use M3</span>
+
(see the instrument [[The RIMO|RIMOs]]).
  
−
The methodology for computing effective beams for a scanning CMB experiment like Planck was presented in our paper: http://arxiv.org/pdf/1005.1929
+
<!--
  
−
  For easy access to the FEBeCoP  beams and PSFs computed on NERSC, they have been transferred to magiqueIII. They are currently stored at two locations:
+
*HFI - LFI_RIMO_DX9_PTCOR6 - {{PLASingleFile|fileType=rimo|name=HFI_RIMO_R1.00.fits|link=The HFI RIMO}}
 +
*LFI - HFI-RIMO-3_16_detilt_t2_ptcor6.fits - {{PLASingleFile|fileType=rimo|name=LFI_RIMO_R1.12.fits|link=The LFI RIMO}}
 +
[[Beams LFI#Effective beams|LFI effective beams]]
 +
-->
  
−
1. Hard disk: /space/SimuData/effBeam_HFI_v41
+
===Beam cutoff radii===
−
2. DMC group: /data/dmc/MISS01/DATA/FEBeCoP_v41
+
N times geometric mean of FWHM of all detectors in a channel, where N
  
−
The gory details of how binary data is organized in the files / DMC objects are not essential to the user and may also change in the future. Here we present how the FEBeCoP I/O interface (installed and tested on magiqueIII) can be used to read effective beams and PSFs for any given set of pixels.
+
{|border="1" cellpadding="5" cellspacing="0" align="center" style="text-align:center"
 +
|+'''Beam cut off radius'''
 +
| '''channel''' || '''Cutoff Radii in units of fwhm''' || '''fwhm of full beam extent'''
 +
|-
 +
|30 - 44 - 70 || 2.5 ||
 +
|-
 +
|100 || 2.25 || 23.703699
 +
|-
 +
|143 || 3 || 21.057402
 +
|-
 +
|217-353 || 4 || 18.782754
 +
|-
 +
|sub-mm || 4 || 18.327635(545GHz) ;  17.093706(857GHz)
 +
|}
  
 +
===Map resolution for the derived beam data object===
 +
* <math>N_{side} = 1024 </math> for LFI frequency channels
 +
* <math>N_{side} = 2048 </math> for HFI frequency channels
  
−
I/O routines to read effective beams are in:
+
==Related products==
−
http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/src/util/
+
===Monte Carlo simulations===
  
−
At present, the Fortran routines are available as .f90 sources, they will be available as a compiled library in future. getBeam.f90 can be used read beams from the disk and getBeam_PIO.f90 to read from the database.
+
FEBeCoP software enables fast, full-sky convolutions of the sky signals with the Effective beams in pixel domain. Hence, a large number of Monte Carlo simulations of the sky signal maps map convolved with realistically rendered, spatially varying, asymmetric Planck beams can be easily generated. We performed the following steps:
  
−
Example Fortran programs and Makefiles to load beams/PSFs either from disk or from database and make their .fits skymaps are in:
+
* generate the effective beams with FEBeCoP for all frequencies for dDX9 data and Nominal Mission
 +
* generate 100 realizations of maps from a fiducial CMB power spectrum
 +
* convolve each one of these maps with the effective beams using FEBeCoP
 +
* estimate the average of the Power Spectrum of each convolved realization, and 1 <math>\sigma</math> errors
  
−
http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/src/beam_extract_f/
 
−
and
 
−
http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/src/psf_extract_f/
 
  
 +
As FEBeCoP enables fast convolutions of the input signal sky with the effective beam, thousands of simulations are generated. These Monte Carlo simulations of the signal (might it be CMB or a foreground (e.g. dust)) sky along with LevelS+Madam noise simulations were used widely for the analysis of Planck data. A suite of simulations were rendered during the mission tagged as Full Focalplane simulations, FFP#.
 +
For example [[HL-sims#FFP6 data set|FFP6]]
  
−
There are two test programs to make full sky effective beam convolved maps, reading beams either from disk or from database, in:
+
===Beam Window Functions===
−
http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/src/convolve/
+
The '''Transfer Function''' or the '''Beam Window Function'''  <math> W_l </math> relates the true angular power spectra <math>C_l </math> with the observed angular power spectra <math>\widetilde{C}_l </math>:
  
−
List of programs
+
<math>
−
----------------
+
W_l= \widetilde{C}_l / C_l
−
beam_extract_f    : extract beams from disk
+
\label{eqn:wl1}</math>
−
beam_extract_f_PIO : extract beams from database
 
−
psf_extract_f      : extract PSF from disk
 
−
psf_extract_f_PIO  : extract PSF from database
 
−
effConv            : convolve map reading beam from disk
 
−
effConv_PIO        : convolve map reading beam from database
 
  
−
Example parameter files with brief explanations are provided in:
+
Note that, the window function can contain a pixel window function (depending on the definition) and it is {\em not the angular power spectra of the scanbeams}, though, in principle, one may be able to connect them though fairly complicated algebra.
−
http://cvs.planck.fr/cvs/Level2/Task_pkg/HL2_FEBeCoP/params/
 
  
 +
The window functions are estimated by performing Monte-Carlo simulations. We generate several random realisations of the CMB sky starting from a given fiducial <math> C_l </math>, convolve the maps with the pre-computed effective beams, compute the convolved power spectra <math> C^\text{conv}_l </math>, divide by the power spectra of the unconvolved map <math>C^\text{in}_l </math> and average over their ratio. Thus, the estimated window function
  
−
The IDL routines (beaminit.pro and getbeam.pro/getpsf.pro) can be used to read the beams/PSFs from disk. These routines have detailed inbuilt help with easy to use examples.
+
<math>
 +
W^{est}_l  = < C^{conv}_l / C^{in}_l >
 +
\label{eqn:wl2}</math>
  
 +
For subtle reasons, we perform a more rigorous estimation of the window function by comparing C^{conv}_l with convolved power spectra of the input maps convolved with a symmetric Gaussian beam of comparable (but need not be exact) size and then scaling the estimated window function accordingly.
  
 +
Beam window functions are provided in the [[The RIMO#Beam Window Functions|RIMO]].
  
−
Details on the subroutines
 
−
--------------------------
 
−
(Please look at the appropriate routines to get the exact syntax)
 
  
−
The basic scheme to load the beams/PSFs (in Fortran or IDL) has two steps:
+
====Beam Window functions, Wl, for Planck mission====
−
 
+
[[File:plot_dx9_LFI_GB_pix.png | 600px | thumb | center |'''Beam Window functions, Wl, for LFI channels''']]
−
1. Init
+
[[File:plot_dx9_HFI_BS_M12_CMB.png | 600px | thumb | |center |'''Beam Window functions, Wl, for HFI channels''']]
−
 
 
−
function: "beaminit"
 
−
 
 
−
arguments:
 
−
 
 
−
"beaminfo" (output of this routine, users need not worry about this)
 
−
 
 
−
"prefix" is the prefix to the beam files or DMC objects, e.g., for 100GHz beams
 
−
 
 
−
from disk: prefix=/data/smitra/effBeam_HFI_v41/100/beams_
 
−
 
 
−
from DMC: prefix=/data/dmc/MISS01/DATA/FEBeCoP_v41/100_
 
−
 
 
−
 
 
−
2. Read beams/PSFs
 
−
 
 
−
function: "readbeam"/"readpsf"
 
−
 
 
−
arguments:
 
−
 
 
−
"beam"/"psf" structure describes beams/PSFs using the following elements:
 
−
 
 
−
pix    : (int_32) pixel index of the beam centre
 
−
 
 
−
nlist  : (int_32) number of pixels used to describe the beam (typically ~200)
 
−
 
 
−
listpix : (nlist int_32) list of pixel indices describing the beam
 
−
 
 
−
map    : (nlist or 6 x nlist float_32) values at the pixels listed in listpix
 
−
 
 
−
nobs    : (1 or 6 float_64) effective number of observation matrix
 
  
 +
==File Names==
 +
The effective beams are provided by the PLA as FITS files containg HEALPix maps of the beams. For the file names the following convention is used:
 +
*Single beam query: '''beams_FFF_''PixelNumber''.fits'''
 +
**FFF is the channel frequency (one of '''30''', '''44''', '''70''', '''100''', '''143''', '''217''', '''353''', '''545''', '''857''');
 +
** ''PixelNumber'' is the number of the pixel to which the beam corresponds (<math>0</math> - <math>12 \times N_{\rm side}^2 - 1</math>). For the LFI <math>N_{\rm side}=1024</math>, for the HFI <math>N_{\rm side}=2048</math>;
 +
*Multiple beam query: '''beams_FFF_''FirstPixelNumber''-''LastPixelNumber''.zip''' <br /> The compressed files contains a set of files with the beams for the pixels covereing the selected region. FFF as for sinle beam query. The naming convention for the beam files contained in the ''.zip'' file is the same as for single beam queries.
 +
** ''FirstPixelNumber'' is the lowest pixel number for the area covered by the request;
 +
** ''LastPixelNumber'' is the highest pixel number for the area covered by the request;
  
−
"beaminfo" (output of beaminit, no need to worry about this)
+
==File format==
 +
The FITS files provided by the PLA contain HEALPix maps of the beams.
  
−
"pixlist" is the list of pixels for which beam should be loaded
+
== References ==
 +
<References />
  
−
"npixel" number of pixels for which beam should be loaded
 
  
−
----
 
  
  
  
−
 
+
[[Category:Mission products|004]]
−
==File Names==
 
−
 
 
−
==Meta data==
 
−
<span style="color:Red">A detailed description of the data format of each file, including header keywords for fits files, extension names, column names, formats….</span>
 
−
 
 
−
[[Category:Mission science products|004]]
 

Latest revision as of 10:37, 5 February 2015

Product description[edit]

The effective beam is the average of all scanning beams pointing at a certain direction within a given pixel of the sky map for a given scan strategy. It takes into account the coupling between azimuthal asymmetry of the beam and the uneven distribution of scanning angles across the sky. It captures the complete information about the difference between the true and observed image of the sky. The effective beams are, by definition, the objects whose convolution with the true CMB sky produce the observed sky map.

Details of the beam processing are given in the respective pages for HFI and LFI.

The full algebra involving the effective beams for temperature and polarisation was presented in [1], and a discussion of its application to Planck data is given in the appropriate LFI Planck-2013-IV[2], Planck-2015-A05[3] and HFI Planck-2013-VII[4] papers. Relevant details of the processing steps are given in the Effective Beams section of this document.


Comparison of the images of compact sources observed by Planck with FEBeCoP products[edit]

We show here a comparison of the FEBeCoP-derived effective beams, and associated point spread functions, PSF (the transpose of the beam matrix), to the actual images of a few compact sources observed by Planck, for all LFI and HFI frequency channels, as an example. We show below a few panels of source images organized as follows:

  • Row #1- DX9 images of four ERCSC objects with their galactic (l,b) coordinates shown under the color bar
  • Row #2- linear scale FEBeCoP PSFs computed using input scanning beams, Grasp Beams, GB, for LFI and B-Spline beams,BS, Mars12 apodized for the CMB channels and the BS Mars12 for the sub-mm channels, for HFI (see section Inputs below).
  • Row #3- log scale of #2; PSF iso-contours shown in solid line, elliptical Gaussian fit iso-contours shown in broken line
  • Comparison images of compact sources and effective beams, PSFs

  • 30GHz

  • 44GHz

  • 70GHz

  • 100GHz

  • 143GHz

  • 217GHz

  • 353GHz

  • 545GHz

  • 857GHz

Histograms of the effective beam parameters[edit]

Here we present histograms of the three fit parameters - beam FWHM, ellipticity, and orientation with respect to the local meridian and of the beam solid angle. The sky is sampled (pretty sparsely) at 3072 directions which were chosen as HEALpix nside=16 pixel centers for HFI and at 768 directions which were chosen as HEALpix nside=8 pixel centers for LFI. These uniformly sample the sky.

Where beam solid angle is estimated according to the definition: [math] 4 \pi \sum[/math](effbeam)/max(effbeam) i.e., [math] 4 \pi \sum(B_{ij}) / max(B_{ij}) [/math]


Histograms for LFI effective beam parameters
Histograms for HFI effective beam parameters

Sky variation of effective beams solid angle and ellipticity of the best-fit Gaussian[edit]

  • The discontinuities at the Healpix domain edges in the maps are a visual artifact due to the interplay of the discretized effective beam and the Healpix pixel grid.


  • Sky variation of effective beams ellipticity of the best-fit Gaussian

  • ellipticity - 30GHz

  • ellipticity - 44GHz

  • ellipticity - 70GHz

  • ellipticity - 100GHz

  • ellipticity - 143GHz

  • ellipticity - 217GHz

  • ellipticity - 353GHz

  • ellipticity - 545GHz

  • ellipticity - 857GHz


  • Sky (relative) variation of effective beams solid angle of the best-fit Gaussian

  • beam solid angle (relative) variations wrt scanning beam - 30GHz

  • beam solid angle (relative) variations wrt scanning beam - 44GHz

  • beam solid angle (relative) variations wrt scanning beam - 70GHz

  • beam solid angle (relative) variations wrt scanning beam - 100GHz

  • beam solid angle (relative) variations wrt scanning beam - 143GHz

  • beam solid angle (relative) variations wrt scanning beam - 217GHz

  • beam solid angle (relative) variations wrt scanning beam - 353GHz

  • beam solid angle (relative) variations wrt scanning beam - 545GHz

  • beam solid angle (relative) variations wrt scanning beam - 857GHz


  • Sky (relative) variation of effective beams fwhm of the best-fit Gaussian

  • fwhm (relative) variations wrt scanning beam - 30GHz

  • fwhm (relative) variations wrt scanning beam - 44GHz

  • fwhm (relative) variations wrt scanning beam - 70GHz

  • fwhm (relative) variations wrt scanning beam - 100GHz

  • fwhm (relative) variations wrt scanning beam - 143GHz

  • fwhm (relative) variations wrt scanning beam - 217GHz

  • fwhm (relative) variations wrt scanning beam - 353GHz

  • fwhm (relative) variations wrt scanning beam - 545GHz

  • fwhm (relative) variations wrt scanning beam - 857GHz


  • Sky variation of effective beams <math

  • [math]\psi[/math] - 30GHz

  • [math]\psi[/math] - 44GHz

  • [math]\psi[/math] - 70GHz

  • [math]\psi[/math] - 100GHz

  • [math]\psi[/math] - 143GHz

  • [math]\psi[/math] - 217GHz

  • [math]\psi[/math] - 353GHz

  • [math]\psi[/math] - 545GHz

  • [math]\psi[/math] - 857GHz


Statistics of the effective beams computed using FEBeCoP[edit]

We tabulate the simple statistics of FWHM, ellipticity (e), orientation ([math] \psi[/math]) and beam solid angle, ([math] \Omega [/math]), for a sample of 3072 and 768 directions on the sky for HFI and LFI data respectively. Statistics shown in the Table are derived from the histograms shown above.

  • The derived beam parameters are representative of the DPC NSIDE 1024 and 2048 healpix maps (they include the pixel window function).
  • The reported FWHM_eff are derived from the beam solid angles, under a Gaussian approximation. These are best used for flux determination while the the Gaussian fits to the effective beam maps are more suited for source identification.


Statistics of the FEBeCoP Effective Beams Computed with the BS Mars12 apodized for the CMB channels and oversampled
frequency mean(fwhm) [arcmin] sd(fwhm) [arcmin] mean(e) sd(e) mean([math] \psi[/math]) [degree] sd([math] \psi[/math]) [degree] mean([math] \Omega [/math]) [arcmin[math]^{2}[/math]] sd([math] \Omega [/math]) [arcmin[math]^{2}[/math]] FWHM_eff [arcmin]
030 32.239 0.013 1.320 0.031 -0.304 55.349 1189.513 0.842 32.34
044 27.005 0.552 1.034 0.033 0.059 53.767 832.946 31.774 27.12
070 13.252 0.033 1.223 0.026 0.587 55.066 200.742 1.027 13.31
100 9.651 0.014 1.186 0.023 -0.024 55.400 105.778 0.311 9.66
143 7.248 0.015 1.036 0.009 0.383 54.130 59.954 0.246 7.27
217 4.990 0.025 1.177 0.030 0.836 54.999 28.447 0.271 5.01
353 4.818 0.024 1.147 0.028 0.655 54.745 26.714 0.250 4.86
545 4.682 0.044 1.161 0.036 0.544 54.876 26.535 0.339 4.84
857 4.325 0.055 1.393 0.076 0.876 54.779 24.244 0.193 4.63



Beam solid angles for the PCCS[edit]

  • [math]\Omega_{eff}[/math] - is the mean beam solid angle of the effective beam, where beam solid angle is estimated according to the definition: [math]4 \pi \sum [/math](effbeam)/max(effbeam), i.e. as an integral over the full extent of the effective beam, i.e. [math] 4 \pi \sum(B_{ij}) / max(B_{ij}) [/math].
  • from [math]\Omega_{eff}[/math] we estimate the [math]fwhm_{eff}[/math], under a Gaussian approximation - these are tabulated above
    • [math]\Omega^{(1)}_{eff}[/math] is the beam solid angle estimated up to a radius equal to one [math]fwhm_{eff}[/math] and [math]\Omega^{(2)}_{eff}[/math] up to a radius equal to twice the [math]fwhm_{eff}[/math].
      • These were estimated according to the procedure followed in the aperture photometry code for the PCCS: if the pixel centre does not lie within the given radius it is not included (so inclusive=0 in query disc).


Band averaged beam solid angles
Band [math]\Omega_{eff}[/math][arcmin[math]^{2}[/math]] spatial variation [arcmin[math]^{2}[/math]] [math]\Omega^{(1)}_{eff}[/math] [arcmin[math]^{2}[/math]] spatial variation-1 [arcmin[math]^{2}[/math]] [math]\Omega^{(2)}_{eff}[/math] [arcmin[math]^{2}[/math]] spatial variation-2 [arcmin[math]^{2}[/math]]
30 1189.513 0.842 1116.494 2.274 1188.945 0.847
44 832.946 31.774 758.684 29.701 832.168 31.811
70 200.742 1.027 186.260 2.300 200.591 1.027
100 105.778 0.311 100.830 0.410 105.777 0.311
143 59.954 0.246 56.811 0.419 59.952 0.246
217 28.447 0.271 26.442 0.537 28.426 0.271
353 26.714 0.250 24.827 0.435 26.653 0.250
545 26.535 0.339 24.287 0.455 26.302 0.337
857 24.244 0.193 22.646 0.263 23.985 0.191

Production process[edit]

FEBeCoP, or Fast Effective Beam Convolution in Pixel space[1], is an approach to representing and computing effective beams (including both intrinsic beam shapes and the effects of scanning) that comprises the following steps:

  • identify the individual detectors' instantaneous optical response function (presently we use elliptical Gaussian fits of Planck beams from observations of planets; eventually, an arbitrary mathematical representation of the beam can be used on input)
  • follow exactly the Planck scanning, and project the intrinsic beam on the sky at each actual sampling position
  • project instantaneous beams onto the pixelized map over a small region (typically <2.5 FWHM diameter)
  • add up all beams that cross the same pixel and its vicinity over the observing period of interest
  • create a data object of all beams pointed at all N'_pix_' directions of pixels in the map at a resolution at which this precomputation was executed (dimension N'_pix_' x a few hundred)
  • use the resulting beam object for very fast convolution of all sky signals with the effective optical response of the observing mission


Computation of the effective beams at each pixel for every detector is a challenging task for high resolution experiments. FEBeCoP is an efficient algorithm and implementation which enabled us to compute the pixel based effective beams using moderate computational resources. The algorithm used different mathematical and computational techniques to bring down the computation cost to a practical level, whereby several estimations of the effective beams were possible for all Planck detectors for different scan and beam models, as well as different lengths of datasets.


Pixel Ordered Detector Angles (PODA)[edit]

The main challenge in computing the effective beams is to go through the trillion samples, which gets severely limited by I/O. In the first stage, for a given dataset, ordered lists of pointing angles for each pixel - the Pixel Ordered Detector Angles (PODA) are made. This is an one-time process for each dataset. We used computers with large memory and used tedious memory management bookkeeping to make this step efficient.

effBeam[edit]

The effBeam part makes use of the precomputed PODA and unsynchronized reading from the disk to compute the beam. Here we tried to made sure that no repetition occurs in evaluating a trigonometric quantity.


One important reason for separating the two steps is that they use different schemes of parallel computing. The PODA part requires parallelisation over time-order-data samples, while the effBeam part requires distribution of pixels among different computers.


Computational Cost[edit]

The computation of the effective beams has been performed at the NERSC Supercomputing Center. The table below shows the computation cost for FEBeCoP processing of the nominal mission.

Computational cost for PODA, Effective Beam and single map convolution. Wall-clock time is given as a guide, as found on the NERSC supercomputers.
Channel 030 044 070 100 143 217 353 545 857
PODA/Detector Computation time (CPU hrs) 85 100 250 500 500 500 500 500 500
PODA/Detector Computation time (wall clock hrs) 7 10 20 20 20 20 20 20 20
Beam/Channel Computation time (CPU hrs) 900 2000 2300 2800 3800 3200 3000 900 1100
Beam/Channel Computation time (wall clock hrs) 0.5 0.8 1 1.5 2 1.2 1 0.5 0.5
Convolution Computation time (CPU hr) 1 1.2 1.3 3.6 4.8 4.0 4.1 4.1 3.7
Convolution Computation time (wall clock sec) 1 1 1 4 4 4 4 4 4
Effective Beam Size (GB) 173 123 28 187 182 146 132 139 124


The computation cost, especially for PODA and Convolution, is heavily limited by the I/O capacity of the disc and so it depends on the overall usage of the cluster done by other users.

Inputs[edit]

In order to fix the convention of presentation of the scanning and effective beams, we show the classic view of the Planck focal plane as seen by the incoming CMB photon. The scan direction is marked, and the toward the center of the focal plane is at the 85 deg angle w.r.t spin axis pointing upward in the picture.


Planck Focal Plane


The Focal Plane DataBase (FPDB)[edit]

The FPDB contains information on each detector, e.g., the orientation of the polarisation axis, different weight factors, (see the instrument RIMOs):


The scanning strategy[edit]

The scanning strategy, the three pointing angle for each detector for each sample: Detector pointings for the nominal mission covers about 15 months of observation from Operational Day (OD) 91 to OD 563 covering 3 surveys and half.

The scanbeam[edit]

The scanbeam modeled for each detector through the observation of planets. Which was assumed to be constant over the whole mission, though FEBeCoP could be used for a few sets of scanbeams too.

  • LFI: GRASP scanning beam - the scanning beams used are based on Radio Frequency Tuned Model (RFTM) smeared to simulate the in-flight optical response.
  • HFI: B-Spline, BS based on 2 observations of Mars.

(see the instrument RIMOs).


Beam cutoff radii[edit]

N times geometric mean of FWHM of all detectors in a channel, where N

Beam cut off radius
channel Cutoff Radii in units of fwhm fwhm of full beam extent
30 - 44 - 70 2.5
100 2.25 23.703699
143 3 21.057402
217-353 4 18.782754
sub-mm 4 18.327635(545GHz) ; 17.093706(857GHz)

Map resolution for the derived beam data object[edit]

  • [math]N_{side} = 1024 [/math] for LFI frequency channels
  • [math]N_{side} = 2048 [/math] for HFI frequency channels

Related products[edit]

Monte Carlo simulations[edit]

FEBeCoP software enables fast, full-sky convolutions of the sky signals with the Effective beams in pixel domain. Hence, a large number of Monte Carlo simulations of the sky signal maps map convolved with realistically rendered, spatially varying, asymmetric Planck beams can be easily generated. We performed the following steps:

  • generate the effective beams with FEBeCoP for all frequencies for dDX9 data and Nominal Mission
  • generate 100 realizations of maps from a fiducial CMB power spectrum
  • convolve each one of these maps with the effective beams using FEBeCoP
  • estimate the average of the Power Spectrum of each convolved realization, and 1 [math]\sigma[/math] errors


As FEBeCoP enables fast convolutions of the input signal sky with the effective beam, thousands of simulations are generated. These Monte Carlo simulations of the signal (might it be CMB or a foreground (e.g. dust)) sky along with LevelS+Madam noise simulations were used widely for the analysis of Planck data. A suite of simulations were rendered during the mission tagged as Full Focalplane simulations, FFP#. For example FFP6

Beam Window Functions[edit]

The Transfer Function or the Beam Window Function [math] W_l [/math] relates the true angular power spectra [math]C_l [/math] with the observed angular power spectra [math]\widetilde{C}_l [/math]:

[math] W_l= \widetilde{C}_l / C_l \label{eqn:wl1}[/math]

Note that, the window function can contain a pixel window function (depending on the definition) and it is {\em not the angular power spectra of the scanbeams}, though, in principle, one may be able to connect them though fairly complicated algebra.

The window functions are estimated by performing Monte-Carlo simulations. We generate several random realisations of the CMB sky starting from a given fiducial [math] C_l [/math], convolve the maps with the pre-computed effective beams, compute the convolved power spectra [math] C^\text{conv}_l [/math], divide by the power spectra of the unconvolved map [math]C^\text{in}_l [/math] and average over their ratio. Thus, the estimated window function

[math] W^{est}_l = \lt C^{conv}_l / C^{in}_l \gt \label{eqn:wl2}[/math]

For subtle reasons, we perform a more rigorous estimation of the window function by comparing C^{conv}_l with convolved power spectra of the input maps convolved with a symmetric Gaussian beam of comparable (but need not be exact) size and then scaling the estimated window function accordingly.

Beam window functions are provided in the RIMO.


Beam Window functions, Wl, for Planck mission[edit]

Beam Window functions, Wl, for LFI channels
Beam Window functions, Wl, for HFI channels

File Names[edit]

The effective beams are provided by the PLA as FITS files containg HEALPix maps of the beams. For the file names the following convention is used:

  • Single beam query: beams_FFF_PixelNumber.fits
    • FFF is the channel frequency (one of 30, 44, 70, 100, 143, 217, 353, 545, 857);
    • PixelNumber is the number of the pixel to which the beam corresponds ([math]0[/math] - [math]12 \times N_{\rm side}^2 - 1[/math]). For the LFI [math]N_{\rm side}=1024[/math], for the HFI [math]N_{\rm side}=2048[/math];
  • Multiple beam query: beams_FFF_FirstPixelNumber-LastPixelNumber.zip
    The compressed files contains a set of files with the beams for the pixels covereing the selected region. FFF as for sinle beam query. The naming convention for the beam files contained in the .zip file is the same as for single beam queries.
    • FirstPixelNumber is the lowest pixel number for the area covered by the request;
    • LastPixelNumber is the highest pixel number for the area covered by the request;

File format[edit]

The FITS files provided by the PLA contain HEALPix maps of the beams.

References[edit]

  1. ↑ 1.01.1 Fast Pixel Space Convolution for Cosmic Microwave Background Surveys with Asymmetric Beams and Complex Scan Strategies: FEBeCoP, S. Mitra, G. Rocha, K. M. Górski, K. M. Huffenberger, H. K. Eriksen, M. A. J. Ashdown, C. R. Lawrence, ApJS, 193, 5-+, (2011).
  2. ↑ Planck 2013 results. IV. Low Frequency Instrument beams and window functions, Planck Collaboration, 2014, A&A, 571, A4
  3. ↑ Planck 2015 results. IV. LFI beams and window functions, Planck Collaboration, 2016, A&A, 594, A4.
  4. ↑ Planck 2013 results. VII. HFI time response and beams, Planck Collaboration, 2014, A&A, 571, A7

Cosmic Microwave background

(Planck) Low Frequency Instrument

(Planck) High Frequency Instrument

Early Release Compact Source Catalog

Full-Width-at-Half-Maximum

Data Processing Center

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 Legacy Archive

Flexible Image Transfer Specification

(Hierarchical Equal Area isoLatitude Pixelation of a sphere, <ref name="Template:Gorski2005">HEALPix: A Framework for High-Resolution Discretization and Fast Analysis of Data Distributed on the Sphere, K. M. Górski, E. Hivon, A. J. Banday, B. D. Wandelt, F. K. Hansen, M. Reinecke, M. Bartelmann, ApJ, 622, 759-771, (2005).

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