[alma-config] Imaging Simulations

[John Conway]

Hi Min et al,

 OK I can easily run sumulations for my two test images
with the two-ring configurations you suggest below. 
If this is the currently most favoured ring-like model
This might be a more useful version for a submitted
memo version.


    John


 



On Tue, 18 Jan 2000, Min Yun wrote:

> Hi John,
> 
> It is a nice and substantial work.  I still have not gotten back
> to you on my comments to your ALMA draft memo, and I will return
> those comments along with more detailed comments on the current
> one.  Just repeating Bryan's point, the comparison will be more
> meaningful if you used a double ring configuration rather than
> a single ring.  If you do not have an example of such a configuration,
> you can pick it up as www.aoc.nrao.edu/~myun/mma/64_DONUT_0.25 --
> this is an ascii table with 64 antennas arranged in two rings,
> one with a 3km diameter and one with 1.5km diameter.  It is part
> of the summary of my URSI Toronto talk 
> (www.aoc.nrao.edu/~myun/mma/straw_config.html).  I am glad to hear
> that you are also addressing the issue on snapshot vs. long track.
> It is one of the topics I wanted to cover for tomorrow's telecon.
> I hope you will be able to join us.  Cheers!
> 
> 
> 
> 					-- Min
> 
> 
> 
> > From owner-alma-config at kochab.cv.nrao.edu Tue Jan 18 05:12 MST 2000
> > Date: Tue, 18 Jan 2000 13:09:01 +0100 (CET)
> > From: John Conway <jconway at oso.chalmers.se>
> > To: alma-config at cv3.cv.nrao.edu
> > cc: jconway at oso.chalmers.se
> > Subject: [alma-config] Imaging Simulations
> > MIME-Version: 1.0
> > 
> > 
> > I have been doing some CLEAN imaging simulations comparing
> > snapshot and long track imaging with a spiral zoom array, 
> > for the case of two realistic images.
> > 
> > The results can be found at
> > http://www.oso.chalmers.se/~jconway/ALMA/SIMULATIONS/ 
> > Let me know if you have any problems reading it or if
> > reads too slow.
> > 
> > The title and abstract are given below.
> > 
> >   Cheers
> >       John.
> > 
> > 
> > ---------------------------------------------------------------
> > 
> > TITLE  Imaging Simulations with a Spiral Zoom Array; 
> > Comparisons with Ring Arrays 
> > 
> > 
> > ABSTRACT 
> > 
> > Imaging simulations have been carried out with a version of the spiral
> > zoom array presented in ALMA memo 283. Two test images were
> > used, one based on a VLA image of Cygnus A and another based on an OVRO CO
> > map of M51. Both snapshot and long track CLEAN
> > simulations were carried out. The results were compared with those
> > obtained for a ring array giving similar resolution. In each case the
> > spiral array gave better imaging performance. The difference was
> > particularly large for the case of the long-track observations when the
> > rms errors were 10 times larger for the ring than for the spiral arrays.
> > This large difference arises because the large near-in sidelobes of ring
> > arrays, caused by the sharp edge to the uv-coverage, persists even after a
> > long track. 
> > 
> > These simulations illustrate that it is important to consider that
> > deconvolution requires both extrapolation of the uv data as well as
> > interpolation between uv points. A naturally tapered uv coverage such as
> > that provided by a spiral zoom array provides more constraints on
> > the necessary extrapolation than for the case of ring arrays. More imaging
> > simulations must be done before final conclusion can be drawn;
> > however these initial tests show that, at least for a broad class of
> > realistic images, spiral zoom arrays can have superior imaging
> > performance as well as superior observing efficiency as compared 
> > to fixed ring arrays. 
> > 
> > 
>