[alma-config] telecon this Wednesday

[Mark Holdaway]

> > I think the near-in sidelobe levels reported by Morita for the
> > spiral array are in error -- I believe they are the main beam's
> > wings rather than sidelobes -- this may be relevant or irrelevant,
> > I don't know.  I suppose it would make more sense to look at the
> > deviation from a Gaussian.  While it is true that the near-in sidelobes
> > of the spiral configuration will not be reduced by earth rotation,
> > I contend that they start out much smaller than the ring or donut
> > configurations near in sidelobes.
> This raises an interesting issue -- do you really want a PSF that has
> a long tail?  I remember trying to combine the VLA C and D array
> data in a "dumb" way, and the resulting PSF with a plateau posed a
> major problem in deconvolution, not surprisingly.  Even when not
> being so dumb, what one really wants is a truncated Gaussian rather than
> honest goodness Gaussian, isn't it?
> 

Running out of steam.  Looking at Morita's beam slice, his PSF does not
have a wide plateau.  Its a very well behaved beam.  Its not clear if you
want a truncated Gaussian, as that would have some issues in the Fourier
plane at the large spatial frequencies.

> > Similarly, I contend that if Leonia did an optimiazation over a long
> > integration, the outer sidelobes would be small due to earth rotation
> > averaging down, so the algorithm would concentrate more on reducing the
> > inner sidelobes via structural means, ie, by moving antennas.
> Leonia's routine in practice only works on the near-in sidelobes.  You can
> make the optimization region as large as you want, but this drives
> you do the solution space which is not particularly unique.  Again,
> this is why my current strawperson donut configurations have only 5% 
> sidelobes rather than "bigger than 10%" number routinely thrown around.

Hey, 5% is whats in my head.  Bigger tha 10% is ring array city.  (If
Barry can say "thingee", I can say "ring array city".)  While the
distinction is blurred for nearin and far out, I would count anything
beyond 5 or 10 synthesized beam widths to be "far out" sidelobes, anything
within 5 as near in.  So, for your optimizations, there is a third
region: the unoptimized far-out region, which could be problematic
for some observations.


As to your experience of being sensitivity limited in VLA proposals,
thats a selection effect based upon your kind of science.  Admittedly,
sensitivity is probably dominant at this point.

	-Mark