[alma-config] Re: Imaging Simulations

[John Conway]

On Wed, 19 Jan 2000, Simon Radford wrote:

> 
> John,
> 
> Your results of your simulations should provoke some lively discussion.
> A couple of points:
>

 
> -- As Mark Holdaway has often pointed out to me, a centrally condensed
> configuration, such as your spiral, requires more physical real estate
> than a ring configuration for the same nominal resolution. If I read
> your (proto-)memo correctly, you compared a 3 km spiral to a 1.5 km
> ring. This is, of course, an important trade-off. Since the maximum
> extent of the ALMA configurations is fixed (3 and 10 km) by various
> constraints, the trade-off becomes higher resolution (uniform uv
> illumination) vs. better overall imaging quality (Gaussian uv
> illumination).
> 

This is an important point, thats why the array in memo 283 
and in my web page smoothly joins to a 3km ring.  Going from 
the largest spiral of size 3km to the ring of 3km diameter 
provides an extra factor of two in resolution. For a limited
size of real estate of course the optimum resolution is 
achieved by putting all telecopes on the perimeter of that 
real estate.  Adding the extra final ring to achieve 
maximum resolution from the land doesn't cost very many
extra pads and is probably worth it.    

> -- You make an analogy to the effective uv coverage of an optical
> telescope. Another analogy is Single dish radio telescopes, which are
> almost always illuminated with a Gaussian taper, at least at mm
> wavelengths.
>

good pint
 
> Simon
> 
> PS: In section 5, you speak of a "small *increase* in resolution" for
> the long track observations because the east-west beam size increases to
> 147 mas from 135 mas. You mean *decrease* in resolution, don't you?
> 

yes of course your right I'll change this.