WISE Software Interface Specification; fco01; (WSDC D-I125)

Written by F. Masci, version 1.0, 03/24/2009


Interface Name:     Interpolated single-frame co-add products:
                    "int", "unc", and "cov" (level-2a and 2b frames)


Type of Interface:  FITS-Formatted 32-bit frames from "wawaic" pipeline


Read By:            EXEC _____________________________ T. Conrow 


Written/Updated By: AWAIC ____________________________ F. Masci
                    (A WISE Astronomical Image Co-adder
                     executed through the "wawaic" wrapper)


DESCRIPTION:

Level-2a frames:

These are internal intermediate FITS products to enable the first round of
source extraction to support single frame position reconstruction (SFPRex).
The band frames first need to be interpolated onto a common grid to enable 
simultaneous source detection across bands. This is accomplished by the 
AWAIC module (see the COADD Subsystem Design Specification: WSDC D-D019).
There are three FITS image products per band: an intensity (int),
uncertainty (unc), and effective pixel-coverage image (cov); see generic
filenames below. The intensity and uncertainty pixel values are
intrumentally calibrated and have units of DN. The coverage image is
dimensionless and indicates the effective contribution of the Point Response
Function (PRF) to each pixel. It's important to note that the WCS pointing
keywords in the level 2a frames (as shown below) correspond to that generated
by raw ADCS telemetry. They are accurate to a few arcminutes.

Level-2b frames:

These are also internal intermediate FITS products. These are similar to the 
2a's except that they are astrometrically calibrated, i.e., their WCS
pointing (primarily CRVAL1, CRVAL2, CROTA2) corresponds to reconstructed
or refined values computed by SFPRex. These frames are used for the final round
of multi-band source detection to support creation of the single-frame
source catalog.  


FITS HEADER:

Below is an example of a level-2a or 2b FITS image header. Keyword values are
not realistic. These are primarily written by the AWAIC module.

   SIMPLE  =                    T / file does conform to FITS standard
   BITPIX  =                  -32 / number of bits per data pixel
   NAXIS   =                    2 / number of data axes
   NAXIS1  =                 2054 / length of data axis 1
   NAXIS2  =                 2054 / length of data axis 2
   EXTEND  =                    T / FITS dataset may contain extensions
   COMMENT   FITS (Flexible Image Transport System) format is
             defined in 'Astronomy and Astrophysics', volume 376,
             page 359; bibcode: 2001A&A...376..359H
   CRVAL1  =           346.620270 / RA at CRPIX1,CRPIX2, J2000.0 (deg)
   CRVAL2  =            24.723413 / Dec at CRPIX1,CRPIX2, J2000.0 (deg)
   EQUINOX =               2000.0 / Equinox of WCS, (year)
   CTYPE1  = 'RA---SIN'           / Projection type for axis 1
   CTYPE2  = 'DEC--SIN'           / Projection type for axis 2
   CRPIX1  =          1027.500000 / Axis 1 reference pixel at CRVAL1,CRVAL2
   CRPIX2  =          1027.500000 / Axis 2 reference pixel at CRVAL1,CRVAL2
   CDELT1  =  -0.0003819444391411 / Axis 1 scale at CRPIX1,CRPIX2 (deg/pix)
   CDELT2  =   0.0003819444391411 / Axis 2 scale at CRPIX1,CRPIX2 (deg/pix)
   CROTA2  =           295.960723 / Image twist: +axis2 W of N, J2000.0 (deg)
   BITMASK =                    4 / Fatal bitstring mask template
   HISTORY aWaic: A WISE Astronomical Image Coadder; Vsn 4.1
   DATE    = '2009-03-05T20:34:41' / file creation date (YYYY-MM-DDThh:mm:ss UT)
   END


FILE NAMES:

The generic names for the three FITS image products for level-2a/b frames are:

   <scan/frameid>-w<band>-int-2a.fits
   <scan/frameid>-w<band>-unc-2a.fits
   <scan/frameid>-w<band>-cov-2a.fits

   <scan/frameid>-w<band>-int-2b.fits
   <scan/frameid>-w<band>-unc-2b.fits
   <scan/frameid>-w<band>-cov-2b.fits

where angle brackets indicate information whose literal content depends
on actual execution circumstances and

   "int" = interpolated main intensity image frame with pixel values in
           reduced DN
   "unc" = corresponding 1-sigma uncertainty image frame with pixel 
           values in reduced DN
   "cov" = corresponding effective pixel coverage map