[arbitrary string] Re: [mmaswg] Re: [mmaimcal] Dynamic Scheduling

[Mark Holdaway]

On Dynamic Scheduling:

I found from my simulations of a distribution of observing frequencies
and the phase stability of the site, assuming fast switching phase
calibration, that phase stability was still the limiting factor:
ie,  the times of good phase stability are not particularly correlated
with the times of good opacity, and the integrated sensitivity of the
array over all projects for a distribution of observing frequencies
is optimized by matching the good phase stability conditions to the 
high frequency projects, rather than matching the good opacity conditions
to the high frequency projects.  (The loss in sensitivity by opacity is
obvious; the loss in sensitivity by phase stability is due to faster
switching -- ie, less time on source -- and larger residual phase errors
-- ie, higher decorrelation;  there is an analogous, but different,
sensitivity loss for radiometric phase correction, but I don't think
anyone is in a possition to estimate what that is at this moment.)

I think satelite imagery will not tell us much about phase stability on
the site.

To further Bryan's vivid story about variable conditions across the VLA
(A array, I hope!), differences in phase stability between the MMA site
and the LMSA site some 10km distant indicate that while the median phase
conditions are very similar, one site or the other can be up to 10 times
worse at any given instant (thats an extreme case; typically the two
sites are within a factor of 2 in rms phase). There are phase disturbances
that cross one site which do not corss the other site.  SO: especially
for phase stability, it is important to monitor across the array.  While
I would argue for a stand-alone instrument like Simon's phase-o-meter,
it is too costly to sample the phase across the array that way -- we
will also need to rely upon data culled from the telescope itself (ie,
phase stability across the array as calculated from coincidental
observations of calibrators).

I'll spare you similar diatribes on wind/solar-pointing and anomalous
refraction-pointing affecting mosaicing and high frequency observations,
and opacity. 

	-M