2015 Scanning Beams

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LFI(Planck) Low Frequency Instrument beams

We released maps of the Stokes parameters of the band-averaged scanning beams. The averages are performed using the RIMO bandpass, assuming a flat spectrum of the incoming radiation. The Stokes parameters maps contain the complete information about the field intensity and polarization properties. Main Beam, Intermediate Beam, and Sidelobes are released separately.

More information on LFI(Planck) Low Frequency Instrument beams can be found at Planck-2015-A04[1] and on HFI(Planck) High Frequency Instrument beams at Planck-2015-A07[2]

File Names

The file names are of the form:

LFI(Planck) Low Frequency Instrument_ScanBeam-{mb,ib,sl}_{fff}-{rrr}_R2.{nn}.stokes

where

  • fff denotes the frequency
  • mb denotes the Main Beams
  • ib denotes the Intermediate Beam
  • sl denotes the Sidelobes
  • rrr denotes the radiometer
  • R2.nn is the version.


At the present time, HFI(Planck) High Frequency Instrument is not releasing the Scanning Beams.

FITSFlexible Image Transfer Specification file structure

The FITSFlexible Image Transfer Specification files contain a primary extension with no data and a minimal header, and one BINTABLE extension with data and with a description of the data in the header keywords. The BINTABLE extension consist in four columns, each containing the array of one Stokes parameter. The columns are called:

  • Beamdata , containing [math]I[/math]
  • BeamdataQ, containing [math]Q[/math]
  • BeamdataU, containing [math]U[/math]
  • BeamdataV, containing [math]V[/math].

Main Beam, Intermediate Beams and Sidelobes are saved with a different data format:

  • Main Beams are projected on the tangent plane to the sphere, and sampled on a grid. The grid include an angular region expressed by the keyword angularCut, and its dimensions are given by the keywords Nx and Ny, representing the number of columns and rows. Each column of the BINDATA extension contains the sequence of the [math]Nx \times Ny[/math] samples of the map in row major order. The keywords Xcentre and Ycentre express the coordinates of the beam maximum (i.e. where the sphere intersect the tangent plane).
Main Beam file structure
Column Name Data Type Units Description Comment
BEAMDATA Real*4 none Stokes parameter I
BEAMDATAQ Real*4 none Stokes parameter Q
BEAMDATAU Real*4 none Stokes parameter U
BEAMDATAV Real*4 none Stokes parameter V
Keyword Data Type Value Description Comment
Nx Int 601 X axis samples number X axis aligned with the direction of the S arm
Ny Int 601 Y axis samples number Y axis aligned with the direction of the M arm
Xcentre Int 301 X coordinate of the beam centre
Ycentre Int 301 Y coordinate of the beam centre
Xdelta Float X step in radians
Ydelta Float Y step in radians



  • Intermediate Beams and Sidelobes are sampled on the sphere. The resolution in [math]\theta[/math] and [math]\phi[/math] is given by the keywords "Ntheta" and "Nphi". The columns of the BINDATA extension contain the sequence of Nphi Stokes parameters for each [math]\theta[/math].
Intermediate Beam and Sidelobes file structure
Column Name Data Type Units Description Comment
BEAMDATA Real*4 none Stokes parameter I
BEAMDATAQ Real*4 none Stokes parameter Q
BEAMDATAU Real*4 none Stokes parameter U
BEAMDATAV Real*4 none Stokes parameter V
Keyword Data Type Value Description Comment
Ntheta Int [math]\theta[/math] samples number colatitude
Nphi Int [math]\phi[/math] samples number longitude
Mintheta Float Minimum value of [math]\theta[/math]
Maxtheta Float Maximum value of [math]\theta[/math]
angularCut Float Angular cut [deg]

HFI(Planck) High Frequency Instrument Beams

The HFI(Planck) High Frequency Instrument scanning beams are a combination of observations of Saturn, for the central parts, and Jupiter, for the wings, as described in the Beams section of this document, and in Section 4.1 of Planck-2015-A07[2] on Hybrid beams. Saturn data are used where they are signal-dominated; when the SNR of Saturn drops to < 9, Jupiter data are used, after binning them azimuthally. Beyond that, i.e., below the noise floor of the Jupiter data, and out to 100 arcmin, a power law (~θ -3) is used, where the exponent is derived from GRASP physical optics models. The figure below, taken from the Beams section of this document, shows graphically the different portions of the beam model.


Scanning beam map for detector 143-6 showing a rough diagram of the regions that are handled with a different data selection or binning.


The beams are provided in FITSFlexible Image Transfer Specification files named

  • HFI(Planck) High Frequency Instrument_ScanBeam_{det-name}_R2.nn.fits,

where det-name is of the form 100-1a, and nn is the version number. Each file contains a single IMAGE extension. The image is 6001x6001 pixels of size 2x2 arcsec2 (given in the DELTAX and DELTAY keywords), centred on pixel 3001,3001, and normalised to 1 at the maximum, where X and Y and in the Dxx reference system.

References

  1. Planck 2015 results. IV. LFI beams and window functions, Planck Collaboration, 2016, A&A, 594, A4.
  2. 2.0 2.1 Planck 2015 results. VII. High Frequency Instrument data processing: Time-ordered information and beam processing, Planck Collaboration, 2016, A&A, 594, A7.