[daip] [Fwd: scimg question]

[Eric Greisen]

Hanno Spreeuw writes:
 > Sorry, please disregard my question (below), I mistakenly assumed that 
 > SCIMG would make image cubes when run on spectral line data, that is not 
 > the case. It makes images, not image cubes.
 > So does SCIMG use the first channel only?

       No - it uses all channels and IFs gridded in the proper
locations in the uv-plane.  The remark in the help file that you
mention is not intended to mean "add up all the channels" - it is
intended to mean, include only channels having the same signal (i.e. a
continuum) but omit any channels with additional spectral-line
signals.  A single gain is found which applies to all channels - it is
hard to tell from the OOP code exactly what all is happeneing.  There
should be messages that will give clues and the final SN table will
tell you whether there is IF-dependent gains or not.  I expect that
the gains will be different for the different IFs.

Eric Greisen


 > 
 > -------- Original Message --------
 > Subject: scimg question
 > Date: Sun, 30 Sep 2007 12:49:28 +0200
 > From: Hanno Spreeuw <hspreeuw at science.uva.nl>
 > Organization: Universiteit van Amsterdam
 > To: daip at nrao.edu
 > 
 > Hello, I have a question about scimg.
 > The scimg helpfile says that one should first transform the spectral
 > line data into a "continuum" data set using split, uvcop, etc.
 > However, if you run scimg on your line data you seem to end up with a
 > datacube which you could then average using sumim.
 > Is this ok?
 > In this way one could avoid bandwidth smearing.
 > I must add that I probably have anough s/n per channel for selfcal (it
 > is P-band VLA data centered on SgrA).
 > Thanks,
 > Hanno.
 > 
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