[daip] imagr

[Eric Greisen]

Shea D. Brown writes:
 > Hello,
 >     I was wondering where imagr gets it's frequency information in the
 > uv-data?
 >      I am reducing WSRT data with AIPS: 8 IFs, 64 channels per IF.  I've
 > used SPLAT to apply a Hanning taper and have selected every other
 > channel to make 32 channels per IF.  The frequencies look correct in
 > the header, but when I make the images with imagr, the images become
 > distorted across an IF, as if imagr is not getting the frequencies
 > correct (the problem then 'resets' when you get to the next IF, only
 > to start distorting again).  I've included the IMHEADER output for my
 > multisource file below.  Thanks for any suggestions on how to hunt
 > down this problem.
 > 
 > Shea Brown
 > University of Minnesota
 > Department of Astronomy
 > 
 > AIPS 1: Telescope=WSRT               Receiver=WSRT
 > AIPS 1: Observer=ProcessD            User #=   77
 > AIPS 1: Observ. date=20-JAN-2006     Map date=31-MAY-2006
 > AIPS 1: # visibilities    200928     Sort order  TB
 > AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  TIME1  BASELINE
 > AIPS 1:            INTTIM  SOURCE  FREQSEL  WEIGHT  SCALE
 > AIPS 1: ----------------------------------------------------------------
 > AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
 > AIPS 1: COMPLEX      1   1.0000000E+00       1.00  1.0000000E+00    0.00
 > AIPS 1: STOKES       4  -1.0000000E+00       1.00 -1.0000000E+00    0.00
 > AIPS 1: FREQ        32   3.8140625E+08       1.00 -3.1250000E+05    0.00
 > AIPS 1: IF           8   1.0000000E+00       1.00  1.0000000E+00    0.00
 > AIPS 1: RA           1    05 42 36.138       1.00       3600.000    0.00
 > AIPS 1: DEC          1    49 51 07.236       1.00       3600.000    0.00
 > AIPS 1: ----------------------------------------------------------------
 > AIPS 1: Coordinate equinox 2000.00
 > AIPS 1: Rest freq      0.000         Vel type: OPTICAL wrt YOU
 > AIPS 1: Alt ref. value  0.00000E+00  wrt pixel    0.50
 > AIPS 1: Maximum version number of extension files of type SU is   1
 > AIPS 1: Maximum version number of extension files of type AN is   1
 > AIPS 1: Maximum version number of extension files of type HI is   1
 > AIPS 1: Maximum version number of extension files of type CL is   2
 > AIPS 1: Maximum version number of extension files of type FQ is   1
 > AIPS 1: Maximum version number of extension files of type NX is   1
 > AIPS 1: Maximum version number of extension files of type BP is   2
 > AIPS 1: Maximum version number of extension files of type FG is   1
 > 

great another telescope observing in lower sideband and not fixing
things (GMRT mixes the 2 bands and really can make a mess).

I need to see the contents of the FQ table which is what is used by
IMAGR to get the frequencies.  The channel increment can even have
opposite signs in different IFs in some cases and that can be found
only from the FQ table.

Eric Greisen