[alma-config] BOUNCE alma-config at majordomo.cv.nrao.edu: Non-member submission from ["David Woody" <dwoody at caltech.edu>]

[Min Yun]

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Date: Mon, 7 Feb 2000 18:03:15 -0500 (EST)
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Subject: BOUNCE alma-config at majordomo.cv.nrao.edu:    Non-member submission from 
["David Woody" <dwoody at caltech.edu>]   
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>From myun at nrao.edu  Mon Feb  7 18:03:11 2000
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From: "David Woody" <dwoody at caltech.edu>
To: "ALMA config" <alma-config at zia.aoc.NRAO.EDU>
Subject: Re: footnote to taper discussion
Date: Mon, 7 Feb 2000 15:08:34 -0800
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The taper issue is easy if you can do the tapering by covering the full UV
disk of interest but just spend less time at the edges were you are going
to apply tapered weighting anyway.  This is what we do at OVRO for
holographic dish maps.  But it is fundamentally different to say you are
just going to skip over most or many of the UV cells at the edge.  You
need the data for "truthful" images but you just don't want as much S/N
or integration time at the edges.

Fortunately, nature is on our side in this situation.  Earth rotation
naturally
gives you ~1/BaseLine integration time for free.  So uniform coverage in
snap shot gives you 1/UV tapering in integration time if you can wait for
the longest baseline to change by one dish diameter.  Thus the UV coverage
calculations and image simulations
should cover an appropriate amount of earth rotation time to get the
weighting ALMA data will have.

The best way to present the UV coverage is using a realistic aperture
illumination function and do a proper calculation of the S/N at each
UV-pixel (~1mx1m) and accumulate the coverage as the earth
rotates.  This shows the real coverage and indicates how
well you can hope to recover the overlap pixels through mosaicing.
*****************************************************
| David Woody
| Assistant Director of Instrumentation
| Owens Valley Radio Observatory
| California Institute of Technology
| 100 Leighton Lane (PO Box 968)
| Big Pine, CA 93513
| 760-938-2075ext111, FAX 760-938-2075
| dwoody at caltech.edu
*****************************************************


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