[mmaimcal] Re: Next ACA Tiger Team telecon 1415 UT 4 Sept

[Mark Holdaway]

Koh-Ichiro wrote:

> Dear Tigers.
> 
> I just made a short memo of my recent ACA imaging simulations with
> "old SDE" package.  Please see at my web site.
> 
> http://www.nro.nao.ac.jp/~morita/CONFIG/ACA_memo_u0904.html
> 
> Here is the short summary.
> 
> 1. In noiseless cases, imaging qualities observed with ALMA+SD+ACA are 
> better than those from ALMA+SD. 
> Merit of ACA is very clear in these cases. 
> 
> 2. The improvement of imaging quality by ACA strongly depends on 
> thermal noise. In my simulation (snap shot mosaic), averaged S/N of 
> ACA visitlities had to be more than 5 to obtain better results. 
> 
> 3. Above results suggest us that science merit of ACA should be 
> considered including the flux distribution of actual targets of ALMA. 
> 
> 4. Noise effect of nonlinear deconvolution is not simple. 
> So, we should also make such simulations with CLEAN. 
> 

I agree absolutely with point 4: MEM breaks down as the noise level
increases.  Even modest amounts of noise can drastically affect the
image quality of a MEM image.  The inclusion of total power improves
the simuation over the interferometer only case ( imaging with MEM
in cases where you don't need total power can be radically affected
by noise, the inclusion of total power as required in mosaicing moderates
the effect of noise a good deal).  

	-M