PSF 5x5 Image    (November 30, 2009)
[qua11 WSDC D-I177, vsn 1.0]

Interface Name:     PSF 5x5 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. This SIS concerns the 5x5
partition; for the single global PSF, see SIS qua10. 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), as described in SIS qua10. For the 5x5 image, 25 such PSF
estimates are constructed, arranged in a 5x5 grid spanning the instrument
array. Each such PSF employs data only from postage stamps with centroids
falling into the corresponding array partition. For W1, W2, and W3, the
partitions are spaced along each axis in 204-pixel ranges except for the fifth,
which is 200 pixels long. For W4, the ranges are 102 and 100, respectively.

For the 5x5 FITS image, the partition images are placed side by side, top to
bottom, in the order of the partitions of the instrument array. This results in
a 135x135 image.


Sample FITS Header:

BITPIX  =                  -32
NAXIS   =                    2                                                  
NAXIS1  =                  135                                                  
NAXIS2  =                  135                                                  
CDELT1  =     -0.0002544299932                                                  
CDELT2  =      0.0002544433519                                                  
COMMENT  Generated by psfgrid vsn 3.6  A90914 on 30-11-09 at  9:35:25           
COMMENT  This is a 5x5 PSF image                                                
COMMENT  no smoothing was performed, interlaced only                            
END