[mmaimcal] Re: [alma-config] Imaging simulations for ACA

[Mark Holdaway]

> >> 2. " smoothed
> >> total power data instead of raw total power data from 12 m
> >> antennas. Improvements of imaging quality have been obtained
> >> by this method."
> >> -- so do you efffectively use only up to ~ 6m spacings from the
> >> 12m antennas ?
> >
> >Yes.  But, I should test different beam width for the smoothing.
> 
>     In fact, this is the only way to minimize the effect of pointing errors
> from the single-dish measurement. These result in phase errors proportional
> to the UV distance, so improvement is obtained by only retaining the
> shortest
> spacings from the 12-m single-dish.  With 12-m SD, 6-m ACA, 12-m ALMA,
> forgetting about close packing constraints, you would cover 0-4 m from the
> 12-m
> antennas, 4-8 m from 6-m ACA, and 8-12 m from the 12-m ALMA. Adding
> close-packing
> at 1.25 D, this becomes 0-5 m, 5-10 m, 10-14 m.
>     So I guess smoothing to the equivalent of a 5-m dish will give you nice
> results.
> 

There is another way: to make the 12-m dishes point better.
I would suggest a cost-benefit analysis here: from studies
like Morita-san's, we can specify a 12-m pointing error which
results in equivalent image quality to the 64 x 12m + 18 x 6m
+ smoothed 12m data.  Which costs more, to build the ACA, or
to make the 12m antennas point better?


I would further argue that we don't need to make all the 12m
antennas point better, as it is mainly the total power measurementes
which are messing up the imaging (there is more flux to be thrown around
here), so it is only the number of antennas that are alotted to total
power measurements (yet another mess to be sorted out) that we need to
make point exceedingly well.

	-Mark