[alma-config] CLEAN and difference results for B arrays

[Bryan Butler]

>In cases like Mars which are dominated by some obvious extended structure,
>there is
>a good general solution which has not been implemented in any package to my
>knowledge.
>I used it a couple of times on my own data and that gives fairly good
>results.
>
>The trick is to remove from the UV data the Fourier component of an original
>model (in the
>case of Mars, a uniform disk would do it, but the model can be completely
>arbitrary). You then
>perform a normal deconvolution of the difference UV data. The last step is
>to add the original
>model to the Clean components found in this deconvolution, convolve it with
>a Clean beam,
>and add the deconvolution residual.

this is in fact implemented in AIPS, though not as a single task.

simply specifying any initial model (as a set of CLEAN components)
does this.  so, some combination of CCMOD (again, i have a modified
version of this which does more arbitrary models) and IMAGR will
do exactly what stephane describes.  if you want to do it more
explicitly (which i've also done in the past), then the individual
steps are all there, you just need to invoke them in the proper
order.

>What I say here can also be applied to MEM deconvolution, of course,
>although in that case you would
>probably prefer to remove a model which is some underestimate of the true
>emission, to take advantage
>of the positivity constraint, implying that you would still have to use a
>default image.

or, use a MEM that doesn't have the positivity constraint.  the
nice thing here is that you can use a default image which is
just 0 everywhere (assuming that you got the initial model pretty
close so that the "residual image" has small flux density everywhere).


	-bryan