PSF 1x1 Image    (November 30, 2009)
[qua10 WSDC D-I176, vsn 1.0]

Interface Name:     PSF 1x1 Image
Type of Interface:  FITS file
Written By:         PSFGRID _________________________________ J. Fowler
Read By:            PSFmoments_______________________________ T. Jarrett
                    WISE QA Application Framework ___________ D. Kirkpatrick


This file is produced by the ops pipeline for each science scan by the
PSFGRID module.

The PSF module makes 9x9-pixel postage stamps centered on each WISE detection
passed to it. Each postage stamp is background-subtracted and volume-normalized
to unity. There are options about how to get the background (read it from the
mdex file or compute it from either the mean or median of the outer rows and
columns of the postage stamp).

The postage stamps are passed to the PSFGRID module, which averages them via a
two-pass process with outlier rejection. Averaging is done separately in a 5x5
partition of the array and in one global average. By default, the latter average
omits data from pixels whose distance from the array center is more than 91.5%
of the distance from the center to a corner. Currently, any postage stamp
containing a NaN or masked pixel is discarded.

Each PSF estimate is constructed in a grid of 3x3 oversampling pixels (hence a
27x27 array). A given postage stamp may be shifted by plus or minus 1 over-
sampling pixel on each axis to position the point-source centroid over the
central oversampling pixel. Averaging may be done by including each array pixel
in all nine projected oversampling pixels beneath it (called "smoothed",because
this convolves the oversampling pixel size into the resulting PSF; selected by
the "-s" command-line option) or only into the one oversampling pixel directly
beneath the array pixel center (called "interlaced"; selected by the "-n"
command-line option, which is also the default).


Sample FITS Header:

BITPIX  =                  -32
NAXIS   =                    2
NAXIS1  =                   27
NAXIS2  =                   27
CDELT1  =     -0.0002544299932
CDELT2  =      0.0002544433519
COMMENT  Generated by psfgrid vsn 3.5  A90506 on  2-09-09 at 10:16:22
COMMENT  This is a PSF image
COMMENT  no smoothing was performed, interlaced only