Wilkinson Microwave Anisotropy Probe DR2

The data made available through this page has been updated. The most recent version of this data may be accessed through https://lambda.gsfc.nasa.gov/product/wmap/current/

Beam Maps

Coordinate System:
Focal Plane
Projection Type:
0.23°- 0.93° (frequency dependent)
R ectilinear, pixelized at 2.4 arcminutes (0.04°)
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The main and near-sidelobe response of each of the 20 WMAP antenna feeds has been mapped in-flight using observations of Jupiter. The 3-year release is comprised of 6 Jupiter observing seasons: Oct/Nov 2001, Feb/Mar 2002, Nov/Dec 2002, Mar/Apr 2003, Dec 2003/Jan 2004, and Apr/May 2004. As a prelude to beam analysis, an archive of calibrated time-ordered observations is constructed, consisting of Jupiter passages within roughly 9.0, 6.5, 5.0, 2.5 and 2.5 degrees of either the A- or B-side beam center for K, Ka, Q, V and W bands respectively. The time-ordered observations are corrected to a fiducial Jupiter distance of 5.2 AU, background subtracted and corrected for aberration. To constrain low signal-to-noise beam pedestals, a hybrid TOD archive is then constructed in which model predictions (Jarosik et al. 2006) are substituted for data at the 17,17,18,19 and 20 dBi levels of K,Ka,Q,V and W respectively. This hybrid beam archive serves as the basis for beam map and window function analysis.

For purposes of constructing beam maps, the data in the hybrid beam TOD archive are assigned to 2.4 arcminute bins on a coordinate grid centered on either the A or B-side focal plane axis. The beam response for each feed is computed from the average temperature in each bin. No correction has been made for the side-A vs. side-B input transmission imbalance.

Beam maps are provided in 10 FITS image format files, one file for each differencing assembly. Each file contains:

  • the beam map for the A side, in mK (antenna temperature)
  • the statistical error of each bin of the A side beam map, in mK (antenna temperature). The statistical error is based on the number of observations in each bin.
  • the beam map for the B side, in mK (antenna temperature)
  • the statistical error of each pixel of the B side beam map, in mK (antenna temperature)

The beam coordinates form an equal area rectangular coordinate system centered on the optic axis of the spacecraft. They are related to coordinates theta (elevation from optic axis) and phi (azimuth about optic axis) as follows:

  • Xbeam = 2*sin(theta/2) * cos(phi)
  • Ybeam = 2*sin(theta/2) * sin(phi)

Beam Radial Profiles

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For each differencing assembly, a symmetrized radial beam profile is computed by fitting the ensemble of individual A- and B-side Jupiter observations in the hybrid TOD data with Hermite polynomials of even order.

The polynomial fits to the data are tabulated in 0.5 arcminute increments, increasing outwards from beam center (radius=0.0) to the cutoff radius chosen for the window function determination. The profiles are normalized to 1.0 at r=0.

Beam Transfer Functions

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Beam transfer functions are computed from the Legendre transform of the Hermite polynomial fit to the hybrid radial beam profile. The window function applicable to power spectra is the square of the beam transfer function.

Beam transfer functions are presented as ASCII tables, with the first column being multipole moment l and the second column the transfer function (amplitude) normalized to 1.0 at l=1.

Additional Information

A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Andrew F. Ptak
LAMBDA Director: Dr. Thomas M. Essinger-Hileman
NASA Official: Dr. Thomas M. Essinger-Hileman
Web Curator: Mr. Michael R. Greason