[mmaimcal] Summary of case for OSF interferometry

[Mark Holdaway]

Al,

Can we get the accuracy of the various methods declassified for this 
discussion?
Also, what is the difference between Out-of-Focus Beam Maps and
Out-of-Focus Holography?

Also, Robert Lucas said that IRAM does interferometric holography using
planets, something which I had discounted in my short writeup --
so you probably WOULD get the sensitivity for panel settings from
1 baseline astronomical holography at the OSF.

The question to ME becomes:
can we set panels at the high site?
If NOT (as has been stated by Jeff), we probably need the
OSF correlator so we can do astronomical holography observations
at the OSF, plus panel settings there; otherwise, we will do
astronomical holography at the high site, bring each antenna down to
adjust panels, and then bring each antenna back up for a second time.
BASICALLY, the trade off is:

The time it takes to set up the 1-baseline correlator and do each 1-baseline
holography measurement

VS

The time it takes to bring each antenna back down and back up again, plus
any commissioning pileups that coccus because you've got a bunch of antennas
at the high site with sub-optimal surfaces (the latter may not be an 
issue, as
we should be able to proceed with most commissioning work at 90 GHz
even with sub-optimal surfaces).

Anyway, thats my take.

-Mark








Alwyn Wootten wrote:

>Folks,
>Truth time is here--comments on the following?
>Holdaway’s simple holography simulation package in AIPS++/glish
>See https://wikio.nrao.edu/bin/view/ALMA/HoloGraphy
>Using two-element interferometric holography and the brightest compact
>celestial radio sources available, we will have enough sensitivity to
>accurately set the panels near the center of the dish, and not at the edge
>of the dish. Alternatively, using a larger cell size (0.4 m) which won't
>permit panel setting, we can very accurately confirm the surface accuracy
>of the dishes.
>Discussion: The basic question: is it worthwhile to set up a correlator at
>the OSF site to do two element holography on astronomical sources?
>Note that second antenna is followed one month later by third—time for
>interferometry at the OSF is very limited.
>NOTE: if we want to do panel settings from astronomical holography at the
>AOS, we will have to wait until we have 10 antennas.
>Alternatives:
>	Tower holography provides setting at one elevation.
>       Photogrammetry provides measure of surface variation as f(el); has
>worked better than expected at ATF (numbers secret?)
>Out of focus beam maps have given good results at ATF (numbers secret?)
>Out of focus holography has given poor results at ATF owing to limitations
>of the evaluation receivers.  (Numbers secret?)
>Need estimate of accuracy at OSF with ALMA receivers.
>I think that the project might not establish an interferometer at the OSF
>and be just as well off.
>
>
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