[mmaimcal] Re: [alma-sw-ssr] question about frequency/band switching speeds and rates

[Mark Holdaway]

Ed,

That is built into the optimization --
In simulations, I make thousands of fake calibrator fields which
are consistent with the source counts as we think we know them
(we'll find out when we get our hands on the ATF 
Prototype Interferometer in a year).
THEN, I look at how far away each CAL is from TARGET, look at
how bright, determine how much time it takes to look at it,
how much time it takes to go there and back, and how different 
the sky is THERE from HERE -- and I select the calibrator 
(and calibration strategy -- time on cal, time on source, etc) 
which produces the best overall sensitivity.

In gauging the effectiveness of Fast Switching, I look at the
statistics of the distributions I get out of the ensemble
of fake calibrator fields.

Admittedly, it has taken me over 10 years to get this as right
as it is today -- not that its perfect yet.  I learned to tie
my shoes in just a few days, though.

   -Mark


> Hi Mark,
> 
>     Yes, your equation and the comparison of the thermal noise
> and residual atmospheric phase fluctuation is the correct way to
> look at fast switching.  One other consideration is the time spent
> on the calibrator.  The trade-off between a strong but more distant
> calibrator with a weaker but closer (to the target) calibrator is
> also interesting.  The more distant calibrator, even if infinite in
> strength may not be as good (in the sense of obtaining a better
> dynamic range on the target source) as a weaker calibrator even if you have
> to increase its integration time to 5 sec or so.  This consideration
> depends on the angular correlation of the phase fluctuations.
> 
> Ed
> 
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