Imaging and Calibration Group

Agenda for meeting Tuesday, 12 Sep 2000 at 4:00pm EDT.

Date: 12 Sep 2000

Time: 4:00 pm EDT (2:00 pm Socorro, 1:00 pm Tucson)

Phone: (804)296-7082 (CV SoundStation Premier Conference phone).

Past ImCal minutes, etc on MMA Imaging and Calibration Division Page

"NSF is also pleased to be playing a leadership role in developing the international partnership for ALMA--the Atacama Large Millimeter Array." --remarks of Dr. Rita Colwell, Director, NSF, at the Dedication of the Green Bank Telescope, August 25, 2000.

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Agenda

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ASAC Meeting -- Wootten

I attended the ASAC meeting at Berkeley, held an ImCal meeting to brief people on the results of that meeting, and prepared and submitted the report of ImCal August activities. Highlights of the meeting included a general agreement that an enhance ALMA, with Japanese collaboration, should include a compact array (ACA), and a complete complement of receivers if possible. There seems general agreement that the ACA will consist of about a dozen antennas of 6m or 8m diameter, operating primarily or solely in a standalone mode. Components of the enhanced ALMA for which there was less enthusiasm included additional 12m antennas, or the particular FX correlator which was described (see below). Calibration was a major point of discussion. All were agreed that the drawbacks of including a cold load in the system were not worth the modest gains which might be realized. Guilloteau recommended further investigation of the semi-transparent calibration scheme mentioned by Plambeck in his ALMA memo. Emerson presented the proposed passband calibration system, which was enthusiastically received by the panel. It seems to offer a particular promise for polarization calibration. Yun presented the state of configuration investigations, currently progressing through a simulation stage. Receivers were discussed but complete consensus could not be reached on ordering within the second priority list of bands, which contains bands 1,4,8 and 10. Woody reviewed the state of 22 GHz water vapor radiometry at OVRO. He has improved the cooled receiver stability and will outfit the remaining five antennas with a goal toward application of phase correction by early 2001. The system works now, but details need improvement; ultimately a delay error of less than 30 microns is a goal. Richer presented a new plan for 183 GHz radiometers--both a Dicke switched and a correlation receiver are planned, both uncooled. The former provides insufficient spectral resolution, in our view, but the latter allows for sideband separation and could be more stable. The meeting closed with a review of antenna progress and test interferometer plans. Jack Welch became Chairman of the ASAC, Ewine van Dishoeck was elected vice chairman. However, since the vice chairman's duties include arranging the next meeting and the ASAC had just met in Leiden, it was decided to meet next March in Florence, the exact date to be set when the ACC meeting date is set.

I also attended the correlator meeting held just after the ASAC meeting. The Europeans presented their plans for their "Digital Hybrid Correlator" based on frequency division into subbands, and a backplane operating at 256 MHz. The incremental improvements of this correlator on the baseline correlator, at least insofar as scientific capabilities go, are to provide 4 bit correlation, more channels (4096) over the broadest bandwidths, and simultaneous broad and narrow band performance at a given frequency. Design is expected to be finished by Dec 2001, including an experimental mockup including reconfigurable elements. A prototype will be built after that in time for a decision point during 2003 for the project. The FX correlator proposed by Japan had a number of drawbacks, for which modifications were suggested by Chikada. As proposed, the finest resolution is 31.25 kHz, which fails by a factor of 8 to be sufficient for the ALMA science. Furthermore, the sensitivity decreases as resolution increases, by 20% at highest resolution. A reduction in the 'X' part of the correlator realized a 50% or so saving over the original $44M cost estimated for this correlator. The proposed modifications will be considered further.

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JRDG Meeting -- Wootten

Marc Rafal shared his impressions. The JRDG decided that incorporation of a cold load would be difficult, and not clearly achieve the accuracy desired.

Various optic designs were considered. A general principle which all could subscribe to was that the optics should be capable of alignment off-site. Carter had ideas for modification of his design, and movement toward a common solution was manifest. Five or so members will meet in Tucson toward the end of September to iterate further.

Several more phone meetings are contemplated, but the next face to face meeting will probably be the February PDR.

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Action Items 1 Aug2000

DECISION: Configurations--where are we? Next phone meeting plans...ACA/THzA?

DECISION: Implementation of 183 GHz WVR?

DECISION: Are the specs for a nutating secondary correct?

DECISION: What is the total power specification on the ALMA?

DECISION: What is the effect of 1/f noise in the HEMT amplifiers of SIS receivers upon our ability to combine total power and interferometric images into a faithful representation of the sky?

Year 2000

January	February	March	April
May	June	July	August
September	October	November	December

May, 1-2	Site Development Discussions	Garching, Germany
May 15-17	Test Interferometer Planning	Tucson, Arizona

Jun, 12-16	2nd IRAM Millimeter Interferometry Summer School	IRAM Grenoble, France
June 19-20	Vertex Antenna PDR	Duisburg, Germany
Jun, 20-27	7th Synthesis Imaging Summer School	Socorro, USA
June 21-22	EIE Antenna PDR	Venice, Italy

October 13

ACC Meeting

Paris, France

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Travel

AW -> Socorro 20-25 May 2000 ------