[daip] Question

[Eric Greisen]

Vicas Dana wrote:
> Hello there,
> 
> I bumped into something I do not understand. I am combining multiple 
> array configuration data sets of new data which has not been Hanning 
> smoothed when observed. I am using CVEL to get the same correct velocity 
> at the central pixel in all data sets and also to Hanning smooth my 
> data. Then I run a UVDEC to get rid of every other channel of my now 
> Hanning smoothed data. After running UVDEC there is a change in my 
> file's header (see below), there is a line saying : phase shifted  in X 
> 0.00 and in Y 1800.00. I was wondering what does that acutally mean and 
> how does it relate to running a UVDEC on my data. Thank you!
> 
> AIPS 1: Image=DDO168    (UV)         Filename=D168.DH     .UVDEC .   1
> AIPS 1: Telescope=VLA                Receiver=VLA
> AIPS 1: Observer=AH927               User #=  527
> AIPS 1: Observ. date=07-JUL-2008     Map date=11-OCT-2009
> AIPS 1: # visibilities    137076     Sort order  TB
> AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  BASELINE  TIME1
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
> AIPS 1: COMPLEX      3   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: STOKES       2  -1.0000000E+00       1.00 -1.0000000E+00    0.00
> AIPS 1: FREQ       109   1.4194122E+09      55.00  1.2207031E+04    0.00
> AIPS 1: IF           1   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: RA           1    13 14 27.900       1.00       3600.000    0.00
> AIPS 1: DEC          1    45 55 09.000       1.00       3600.000    0.00
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Coordinate equinox 2000.00
> AIPS 1: Phase shifted in X      0.000  in Y   1800.000
> AIPS 1: Rest freq   1420.406         Vel type: OPTICAL wrt SUN
> AIPS 1: Alt ref. value  1.92000E+05  wrt pixel  109.00
> AIPS 1: Maximum version number of extension files of type HI 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 OF 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 WX is   1
> AIPS 1: Maximum version number of extension files of type FQ is   1
> AIPS 1: Keyword = 'OBSCHANS'  value =          256
> AIPS 1: Keyword = 'CORRMODE'  value = '2AC     '
> AIPS 1: Keyword = 'SELCHANS'  value =          255
> AIPS 1: Keyword = 'VLAIFS  '  value = 'AC      '
> AIPS 1: Keyword = 'CORRCOEF'  value =           -1

UVDEC had a silly error in which it tried to change the alternate 
reference pixel to account for the freq changes but stepped on the Y 
shift parameter instead.  PUTHEAD may be used to fix this:

'ALTRPIX '     Alternate reference pixel (real*4)
'YSHIFT  '     Phase shift in Dec (real*4, degrees)

KEYV = 0.5,0  for the first keyword and
KEYV=0 for the second.

Eric Greisen