MMA Imaging and Calibration Group

Minutes for meeting Tuesday, 30 May 2000 at 4pm EDT.

Date: 30 May 2000

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

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

Past minutes, etc on MMA Imaging and Calibration Division Page

Minutes

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News. -Wootten

News from other groups at the joint DH meeting. Details in the Joint DH minutes.

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Receivers

Wild and Payne have issued a proposal on Receiver Specifications which they would like comments upon. Review, please, Steve's Receiver Specifications Needed memo, and his proposed polarization specs. Wootten will distill comments into a reply.

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Japan Involvement -Wootten

See Letter to ASAC from Bob Brown.

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Configurations - Morita, Yun

Morita has conducted several simulations for single pointing imaging including antenna pointing errors.

He reports:

'Array configurations used in these simulations are a ring array and a spiral array which was modified from an original John's spiral array. A multi compact Gaussian model was used as a source model. In the case of no pointing error, results shows that we can obtain very high quality images with both arrays, although there are significant differences of image qualities depending on array configuraions and HA coverages. However, when I put some pointing errors, such differences disappears soon. For example, dynamic ranges of no pointing error cases are from 4,000 to 15,000 but from 2,000 to 3,000 for 1 arcsec pointing error and around 1,000 for 2.5 arcsec pointing error at 230 GHz (See attached figures).

	V1. First of Morita's figures.

	V2. Second of Morita's figures.

V3. Third--attached file is a further result of the imaging simulations including the pointing error. Rms pointing error is assumed about 1/20 FWHM of the primary beam. The ring array was used for these simulations. The figure shows the image qualities normalized by those without the pointing error as a function of source size. A 10-compact-Gaussian model was used except for the case of source size of 0, for which a single Gaussian was used. Image quality decrease to about 70 - 80 % for source size = 0. For this case, we can explain as follows. Rms pointing error of about 1/20 FWHM causes visiblity amplitude error about 0.3 % for a point source at the center of the FOV. This error is correspoinding to rms on-source error of about 3.0e-5 because the far sidelobe level is about 1% of the peak. Since rms off-source error without pointing error is about 2.7e-5 (DR=37,000), total off-source error is about 4.0e-5 and corresponding DR is about 70 % of that for no pointing error case.

I am writing a short report and detailed explanation of these simulations will be appeared in the report.

These are preliminary results and I need more simulations using various configurations and source models. At the moment, however, the imaging simulation with pointing errors is limitted by CPU power so current pixel size of the model is 256 x 256. In the case of 1024 x 1024 pixel size and 64 antennas, it takes about 1 hour to calculate visilities for every integration by the most powerful CPU server at Nobeyama! So, unfortunately, I cannot use standard images in the library prepared by Min.' Morita's WWW Report has appeared on his WWW site.

These calculations are very interesting and we should proceed quickly with the simulation machine discussed in Tucson. I think we should have a goal of finishing a first round of simulations by the end of June and proceeding with AIPS++ simulations then, achieving results by July. We will have a phone meeting next week--1pm Eastern time on June 7th.

Action items from the March CoDR will be discussed. This includes the simulation strategy outline.

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Prototype Antenna, Calibration -Mangum

Upcoming Reviews: Test Interferometer plans, Antenna PDR (June 19-22). Mangum calibration protomemo. Any word from the meeting?

The test interferometer plan does not currently include a WVR in the plan. As pointed out in Butler's memo, 183 GHz may be usable some portion of the time from the Plains of San Augustin. This would fit best in the test interferometer plan after decision on the production antennas, on or after April 2003. Wootten will ask Richer if MRAO has made any plans along these lines.

The current Vertex antenna design models indicate that the ALMA/US antenna will be able to turn around in 0.8 seconds assuming a 30'/sec scan rate and a scan time of >2 seconds in OTF mode. The Antenna Group would like to know if this constraint is consistent with our requirements for all of the OTF modes we envision for ALMA. Comments?

In our discussion, we agreed that this may be in the right ballpark. Mangum will ask what the driving function is--presumably something which doesn't excite the resonant frequency of the antenna, estimated to be in the 6-8 Hz range currently.

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Action Items 30May2000

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

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

Send comments to <tcontini@eso.org> Last modified: Tue Feb 22 09:55:07 MET

Travel

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