2015 Scanning beams

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LFI(Planck) Low Frequency Instrument beams

Maps are released 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 parameter maps contain the complete information about the field intensity and polarization properties. The Main Beam, Intermediate Beam, and Sidelobes are released separately.

More information on LFI(Planck) Low Frequency Instrument beams can be found in Planck-2015-A04[1] and on HFI(Planck) High Frequency Instrument beams in 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, as well as one BINTABLE extension with data and with a description of the data in the header keywords. The BINTABLE extension consist of four columns, each containing the array of one Stokes parameter. The columns are:

  • "Beamdata", containing I;
  • "BeamdataQ", containing Q;
  • "BeamdataU", containing U;
  • "BeamdataV", containing V.

The Main Beam, Intermediate Beams, and Sidelobes are saved with a different data format, as described below.

  • Main Beams are projected onto the tangent plane to the sphere, and sampled on a grid. The grid includes 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 a sequence of the Nx×Ny 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 intersects 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 Number of x-axis samples x axis aligned with the direction of the "S" arm
Ny Int 601 Number of y-axis samples 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 θ and φ are given by the keywords "Ntheta" and "Nphi". The columns of the BINDATA extension contain the sequence of Nphi Stokes parameters for each θ.
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 Number of θ samples Colatitude
Nphi Int Number of φ samples Longitude
Mintheta Float Minimum value of θ
Maxtheta Float Maximum value of θ
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 S/N 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 using 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 6001×6001 pixels of size 2arcsec×2arcsec (given in the "DELTAX" and "DELTAY" keywords), centred on pixel 3001,3001, and normalized to 1 at the maximum, where "X" and "Y" and are in the Dxx reference system.

References

  1. Planck 2015 results. IV. LFI beams and window functions, Planck Collaboration, 2016, A&A, 594, A4.
  2. 2.02.1 Planck 2015 results. VII. High Frequency Instrument data processing: Time-ordered information and beam processing, Planck Collaboration, 2016, A&A, 594, A7.