[alma-config] msg from Woody

[Al Wootten]

Dave's email address wasn't recognized by the mailer, so I forward it:

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Reply-To: "David Woody" <dwoody at ovro.caltech.edu>
From: "David Woody" <dwoody at ovro.caltech.edu>
To: "Mark Holdaway" <mholdawa at cv3.cv.nrao.edu>, <alma-config at zia.aoc.NRAO.EDU>
Cc: "Leonia Kogan" <lkogan at zia.aoc.NRAO.EDU>,
        "Stephane Guilloteau" <guillote at iram.fr>
References: <Pine.LNX.4.10.10103291054270.20185-100000 at water.tuc.nrao.edu>
Subject: Re: 
Date: Fri, 30 Mar 2001 13:47:50 -0800
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I agree with almost everything Mark said.  I particularly like
using the PSF to evaluate array configurations.

I would add that the primary beam pattern, PB, is already in
a proper calculation of the true physical PSF.  That is the effect of
the finite antenna size and illumination function should be included
when displaying the PSF.

The effect PSF is indeed a function of where in the primary beam
the source is.  This can be handled by calculating the beam with
a phase gradient across the UV data, but with no gradient across
the illumination pattern.  Or equivalently shifting the PB across the
synthesized or dirty beam.  I don't think we need to apply the PB
twice once for the physical PB and then again for the image reconstruction.
The second application has more to do with weighting and combining
data and not with the real PSF.

I would prefer using peak sidelobe rather than ensemble averaging
for the off beam center PSFs.  I think we want to be able to tell
the astronomers and imaging algorithms at what level features are
believable or must be cleaned and not that on the average that some
feature is believable.  We should minimize the caveats that astronomers
must use in presenting their data.  A single stray sidelobe that produces
a significant erroneous feature is very bad and must be quantitatively
characterized since we don't know a priori where the sources are.

David

****************************************
| David Woody
| Owens Valley Radio Observatory
| P.O. Box 968, 100 Leighton Lane
| Big Pine, CA 93513, USA
| Phone 760-938-2075ext111, FAX 760-938-2075
|dwoody at caltech.edu
****************************************
----- Original Message -----
From: "Mark Holdaway" <mholdawa at cv3.cv.nrao.edu>
To: <alma-config at zia.aoc.NRAO.EDU>
Cc: "Leonia Kogan" <lkogan at zia.aoc.NRAO.EDU>; "Stephane Guilloteau"
<guillote at iram.fr>
Sent: Thursday, March 29, 2001 10:03 AM