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

[Stephane Guilloteau]

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.

Since the Fourier Transform is a linear operation, that works whatever the
model you take. Best results
are obviously obtained when the model leaves as little differences as
possible.

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.


        Stephane