2015 Healpix Rings

General description

The "HealPix Rings", or HPRs, produced by HFI for the 2015 data release, are an intermediate product of the HFI mapmaking progress, as described briefly in Frequency maps. HPRs are produced by binning the TOI data of a pointing period onto a band of Healpix map pixels. As a result of this binning, the data volume is reduced by nearly a factor of ~20

Production process

For each valid bolometer, HPRs are build for the following quantities:

signal

the actual signal, after the treatment described in Timelines TBD after removal of the total dipole and of the bandpass correction

bandpass

this is the bandpass correction that is calculated and used to clean the signal. For some applications a user might wish to see it or to add it back in.

dipole

this is the total dipole, i.e., solar + orbital. This is what is used for the flux calibration and then removed from the TOI signal.

hit count

the number of TOI samples binned into each ring pixel.

phase

the one-dimensional phase along the ring.

φ, θ, and ψ coordinates

the three coordinates, corresponding to the mean coordinates of the TOI samples actually binned into that pixel, as opposed to the pixel coordinates given by the pixelation scheme, and including the position angle ψ.

File Names

Files are named:

HFI_HPR_353-4a-{signal, bandpass, dipole, hit, phase, phi, theta, psi}_R3.00.fits

FITS file structure

The full mission (thus rings 240-26050) are stored in a single file as an image of Nrings x Npixels (25811 x 27664). The image is stored into a single extension of type IMAGE. The coordinate HPRs are encoded as double precision floating point values in order to maintain the needed accuracy, the others are single precision. File sizes are 5.4 and 2.7 GB, respectively.