[alma-config] simulated imaging test

[Min Yun]

Hi John,

I agree entirely that we should use the most complex image one 
can to test each configuration.  My point is that there is an inherent
contradiction in using "complex images with 4 or 5 pixels 
per beam at each array tested and 100 - 200 beams across"
because the field of view set by the primary beam
limits how many synthesized beams you can have for each configuration.
In other words, the E array test image needs to have only 1/16 of
the numbers of pixels as the A array test image unless you want to do
mosaic imaging, which most of us won't.  Instead, what I am advocating
is to use the test images that are the most complex we can have for
the A array and see how the image degrades as the resolution is reduced.
One advantage is the ease of bookkeeping as I mentioned bofore -- we need
only a set of five well defined test images to do the entire variety of 
imaging tests, rather than having variations of each test image for each
configurations (and agreeing on what that should be again and again).
There is a price to pay, which is that the particular test image may not be
the most complex image one can imaging for some other array.
However, that is why we have 5 different types of images, each of
which presumably have structures and challenges at different scales.

I can easily produce test images for the E array that are 16 times the
size of the primary beam, but I just don't see the practical relevance
of such a test in designing a real array.  The fact that a single field
imaging with ALMA in the E-array will only have some 20 resolution 
elements across the primary beam is a fundamental limit we have to
accept and work with.  I hope you are not proposing to test images 
larger than the primary beam.  If I am not following some point in your
argument, can you propose a specific path we might follow from 
this point on?




					-- Min