[alma-config] [mmaimcal] Re: Phone number change! Proposed phone meeting on configurations

[Min Yun]

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>From owner-mmaimcal at kochab.cv.nrao.edu Thu Dec 23 03:54 MST 1999
From: "Stephane Guilloteau" <guillote at iram.fr>
To: "Al Wootten" <awootten at cv3.cv.nrao.edu>, <mmaimcal at polaris.cv.nrao.edu>,
        <efomalon at polaris.cv.nrao.edu>, <mgordon at polaris.cv.nrao.edu>
Cc: "Tamara Helfer" <thelfer at musca.as.arizona.edu>,
        "D. Woody" <dpw at ovro.caltech.edu>, "L. Mundy" <lgm at astro.umd.edu>,
        "Francois Viallefond" <fviallef at maat.obspm.fr>,
        "J. Conway" <jconway at oso.chalmers.se>, "A. Webster" <asw at roe.ac.uk>,
        "Seiichi Sakamoto" <seiichi at nro.nao.ac.jp>,
        "Koh-Ichiro Morita" <morita at nro.nao.ac.jp>
Subject: [mmaimcal] Re: Phone number change! Proposed phone meeting on configurations
Date: Thu, 23 Dec 1999 11:58:39 +0100
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Dear colleagues,


    Due to the tragic circumstances at Plateau de Bure, I have not been able
to join the
phone meeting. Here is a document I had prepared earlier to provide some
guidelines
for the configuration selection. Please comment.

    In addition, we have been working at IRAM to provide simulations tools
(based on
initial developments by Francois Viallefond) within the GILDAS software.
Special effort
have been made to have fast tools to compute dirty beams.  Typical speed for
1 Million visibilities is about 30 sec on a HP-J280 workstation for 10
different tapering
or weighting conditions.

    This will be available in the next release of GILDAS early January.

        Stephane



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A decision tree for the ALMA configuration.


Here are some elements of thinking to prepare the Configuration selection.

Proposition 1)

	Except for the compact configuration, we assume that exact layout of the=
=20
	configuration will not affect the performances: only the style of array ma=
tters.=20
	Accordingly, details of the topography can be accomodated at a later time,
	once an agreement is reached on which style of array we are building.

Proposition 2)

	The location of the compact configuration will depend on the array style.

Proposition 3)

	ALMA will not perform full tracks on sources, but will rather optimize atm=
ospheric=20
	transparency by observing near transit.=20

	A consequence of this proposition is that the synthesized beam aspect rati=
o will=20
	depend on the zenith angle for each source. A global optimization of array=
 aspect=20
	ratio can be performed on source statistics (fraction of sky as function o=
f zenith
	angle, with ponderation if required for special regions).

Proposition 4)

	Metric to assess configuration quality should include
		a) dynamic range
		b) image fidelity
		c) sidelobe level
		d) noise degradation with tapering
		e) noise degradation in intermediate configurations

Proposition 5)
=09
	Single and multi-configuration should be explored in the context of dynami=
c
	scheduling. Optimization as so far given much importance to the single
	configuration "snapshot", but little is available on multi-configuration y=
et.

Proposition 6)

	Enhancement due to the Japanese participation should be taken into account=
.
	This includes possibly an "ultra-compact" array of 7 x 6-8 meter dishes in=
 compact
	hexagon. Location of such an array vis-a-vis the compact array should be d=
iscussed.