widebandpbcor Namespace Reference

Functions
def	widebandpbcor

---

Function Documentation

def widebandpbcor.widebandpbcor	(		vis = '',
			imagename = '',
			nterms = 2,
			threshold = '',
			action = 'pbcor',
			reffreq = '',
			pbmin = 0.2,
			field = '',
			spwlist = [],
			chanlist = [],
			weightlist = []
	)

Wideband PB-correction on the output of the MS-MFS algorithm

   Wide-band Primary-beam correction

    (1) Compute a set of Primary Beams at the specified frequencies
    (2) Calculate Taylor-coefficient images that represent the PB spectrum
    (3) Perform a polynomial division to PB-correct the output Taylor-coefficient
  images from the MS-MFS algorithm ( clean(nterms>1) )
    (4) Recompute spectral index (and curvature) using the corrected Taylor-coefficient images.

   [ Optionally, skip PB-correction, and only recalculate spectral index
      with a different threshold ]

   This is a temporary task, meant for use until projection-based gridding algorithms
   are available via the 'clean' task.

   An output directory named imagename.pbcor.workdirectory is created, and filled with
   an image-cube of the evaluated primary beams at all specified frequencies,
   Taylor-coefficients, and a 'spectral index' due to the primary beam.  
   Note that for the actual pb-correction, only the Taylor-coefficient images are used.
 
   Task parameters :

   vis -- Name of input visibility file
   example : vis = 'ngc5921.ms'
      Only one MS can be specified here, and it must contain at-least one
       timestep of data at all frequencies required to calculate the PB spectrum. 
      ( In case of multiple MSs with different spectral windows, for now, 
        please split/concat a small fraction of the data to form such an MS )

   imagename -- Pre-name of input and output images. Same as in the clean task.           
   example : imagename = 'run1'
      Restored-images ( run1.image.tt0,etc) and residual images ( run1.residual.tt0, etc.. )
      must be available on disk. 

   nterms -- Number of Taylor terms to be used to model the frequency-dependence 
         of the primary beam.
   example : nterms = 2
        nterms must be less than or equal to the number of frequencies specified via
        spwlist, chanlist and weightlist.
        nterms=1 will do a standard division by the average PB computed over all
        specified frequencies.

   threshold -- Flux level in the restored intensity map, below which to not 
             recalculate spectral index. 
   example : threshold = '0.1Jy'

   action -- Choice of PB-correction with spectral-index recalculation
        or only spectral-index recalculation (using the specified threshold)
   example : action='pbcor'  or action='calcalpha'
       
   With action='pbcor', the following output images are created/overwritten.

      - imagename.pbcor.workdirectory  :  This directory contains an image cube with
        PBs at the list of specified frequencies, and Taylor-coefficient images that
        describe the PB spectrum.
           -  imagename.pb.cube : Concatenated cube of PBs 
           -  imagename.pb.tt0, tt1, ... : Taylor coefficients describing the PB spectrum
           -  imagename.pb.alpha : Spectral index of the PB (for information only)
      - imagename.image.pbcor.tt0,tt1,... : Corrected Taylor coefficients
      - imagename.pbcor.image.alpha : Corrected Spectral Index
      - imagename.pbcor.image.alpha.error : New error map.

    With action='calcalpha', the following output images are created/overwritten
      - imagename.image.alpha : Corrected Spectral Index
      - imagename.image.alpha.error : New error map.

   reffreq -- Reference frequency about which the Taylor-expansion is defined.
    example : reffreq = '1.5GHz'
         If left unspecified, it is picked from the input restored image.
         Note : If reffreq was specified during task clean to produce the images
                   it must be specified here. 

   pbmin -- PB gain level below which to not compute Taylor-coefficients or
        apply PB-corrections.
    example : pbmin = 0.1

   field -- Field selection for the Primary Beam calculation. 
    example : field = '3C291'
        This field selection must be identical to that used in 'clean'

   spwlist -- List of SPW ids for which to make separate Primary Beams
   chanlist -- List of channel ids, within the above SPW ids, at which to make PBs.

     example :  spwlist=[0,1,2], chanlist=[32,32,32] 
                  Make PBs at frequencies corresponding to channel 32 of
                  spws 0,1 and 2.
     example :  spwlist=[0,0,0], chanlist=[0,10,20]
                   Make PBs at frequencies corresponding to channels 0,10,20
                   of spw 0
 
           Primary beams are computed at these specified frequencies and 
           for pointings selected by 'field'.  Taylor-coefficients that represent
           the PB spectrum are computed from these images.

   weightlist -- List of relative weights to apply to the PBs selected via the
             spwlist,chanlist parameters. Weights should approximately represent the
             sum-of-weights applicable during imaging each of these frequencies.
      example : weightlist=[0.5,1.0,1.0] 
                         The first frequency had less usable data due to flagged RFI,
                         but the other two had relatively equal weight.
             These weights are applied to the PB spectrum while computing
             PB Taylor-coefficients. Setting weights to anything other than 1.0
             makes a difference only with very lop-sided weights. 

Definition at line 13 of file widebandpbcor.py.

References vla_uvfits_line_sf.verify, and task_widebandpbcor.widebandpbcor().