[mmaimcal] Fiducial Observations

[Steven T. Myers]

We have been hacking at the data rate question, and the problem of
definining just what the scientifically needed rate is keeps coming
up.  In particular, just how many lags per baseline (or baselines
for N lags) you can get out in the 16ms accumulator integration interval
is a fundamental parameter of the system.

A mode I was using as a test case was mode 0: full bandwidth of 2 GHz
with 512 channels (which can be traded between IFs in a pair,
polarizations, and lags) per IF pair per 32x32 antenna array.  The current
design lets you get a lag measurement every 80ns, and thus it would
take 32 x 32 x 512 x 80ns = 42ms to fetch them all.  Is this fast enough.
It appears possible to do this 4x faster but is there need?

It would be good if we could come up with a suite of "standard observation
modes" that are based on real observations likely to be done.  For
example, I could think of some continuum observations using the full
bandwidth and full polarization which would use mode 0: 512 channels
split into 4 polarizations x 128 frequency channels at 15.6 MHz 
resolution.  I wouldnt particularly mind if I had to cut the number
of channels down (32 would be fine at 62.5 MHz) and unless Im mapping
on the fly, I may be able to integrate for much longer than 16ms before
hopping to a calibrator.  If I needed on-the-fly mapping and Im moving
at 0.1 deg/s ( 360"/s ) and I want to oversample x2 the beam at 850 um
(350 GHz), which is 15" FWHM, at 7" intervals (maybe less because its
smeared by the motion), then I need to dump every 20ms and would be using
the 16ms integration time.

Do y'all think it would be good to come up with a half-dozen or so of
these that we can point to when firming up these specs?  I could see
for example Min doing a cosmological line setup in several transitions.
Probably should do a high-resolution wide-field (maser?) spectral
observation.  Probably a high-resolution astro-chemistry line survey.

  -steve

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|:| Steven T. Myers                      |:|  Associate Scientist      |:|
|:| National Radio Astronomy Observatory |:|                           |:|
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|:| smyers at nrao.edu                      |:|  FAX: (505) 835-7027      |:|
|:| http://www.aoc.nrao.edu/~smyers      |:|                           |:|
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