ALMA previous meeting     next meeting

Contact Information

  • 2005-2-15 15:30 UT
  • Duration: 1 hr
  • USA Toll Free Number: 877-874-1919
  • Toll Number: +1-203-320-9891
  • Passcode: 185064
  • Leader: Al Wootten


18 Feb 2005 ANASAC Telecon
18 Feb 2005 NA Board Telecaucus
24 Feb 2005 ALMA Board Telecon Dates for 2005
24-25 Feb 2005 ASAC Face-to-face Garching
21 Mar 2005 IEEE ICASSP Meeting, Philadelphia Session on Radioastronomical instruments
22-24 Mar 2005 JAO/IPT face-to-face, Garching
4 April 2005 ALMA Executive Meeting, Pasadena, CA
5-6 April 2005 AMAC Meeting, Pasadena, CA
7-8 April 2005 ALMA Board Face-to-face meeting, Pasadena, CA.


  1. Old Business The enhanced Agenda from last month's meeting is available. Science IPT notes from last month's telecon.

DUSTY04 collection of papers relevant to ALMA.

  1. New Business--Project news/updates (Wootten, Wilson, Kawabe)
  2. Milestones-- Complete draft ICD between Science and Site Planned 2303d Not Critical
  3. Frequency Switching in Phased Array mode unsupported
  4. Group Activities (all)
  5. Next meeting is on March 15th (15:30 UT)

Science IPT Group Activity Reports

Please include your Group Activity Report here (How to Enter Your Report), or email it to AlWootten

1 Science IPT Rebaselining documents

2 ASAC news Charges received for face-to-face meeting 24-25 Feb in Garching.

3 Antennas ACA will go to the West location.

4 Astronomer Outreach: NRAO Newsletter ESO Newsletter. NRAO ALMA Calendar

Emerson/Laing -- Instrument Scientists

John Conway -- Configuration

A configuration is under study for the ACA in Japan. The current strawman positions are shown in the figure. ACA strawman configuration

Configuration Redesign. Discussion topic:

Were ALMA never to contain the currently planned population of 64 x 12m antennas in the main array, the current approved configuration might not provide the excellent imaging mandated by the Project Plan, depending on the final population of antennas. Were ALMA never to contain more than fifty antennas, the redesigned configuration would probably contain fewer than the currently designed 216 antenna stations. In our judgment, unsupported by detailed design study, an array optimized for fifty antennas might contain thirty or forty fewer antenna stations. This is a possible project rescope.

John earlier designed an array for the first few antennas. As antennas come on line we'll have to decide where to put them. The not much work option is: 'Where to we put the first 50 antennas to optimize the Early Science for that number of antennas?' We would eventually need to do this anyway.

A) I favor a redesign of the 60 element configuration set which would provide good imaging if populated by only fifty antennas. This redesigned configuration could include results of a study aimed at determining whether the 4 x 12m in the ACA might provide useful baelines if they were to be incorporated into the main ALMA array. "best 60 config - 10 + N? additions" Currently, the thought is not to include any ACA pads in the optimization.

B) Completely redesign the array, optimizing for 50 antennas. This is the current strawman, but assume that 2 may be missing from the array at any given moment.

C) Completely redesign the array, optimizing for 50 antennas but with the possibility of eventual expansion to 60 antennas taken into account (sort of an inverse of A). "best 50 config + optimized N? additions" Maybe it is not different at all.

The current strawman is to pursue Option B toward completion before August.

Jeff Mangum -- Calibration

Robert Lucas -- SSR

Michiel Hogerheijde -- DRSP

Robert Laing -- Commissioning and Science Verification

Mark Holdaway/Steve Myers -- Imaging

OK, I've got a personal report, not a group report. I've been doing simulations of how image quality depends upon N ants, and finally got the first batch out of the oven -- sources limited to 1000:1 dynamic range by thermal noise, observed by arrays with 40, 43, 46, 50, and 56 antennas. Too early to say much. Cleaning down to 1 sigma noise level doesn't give great images, but the images continue to improve in fidelity until about 0.2 sigma (ie cleaning way down into the noise), beyond which image improvements are minimal.

Hey, first results: I owe everyone a big apology, my intuition was WRONG! N ants makes a HUGE difference (at least in the simulations I performed this time). Check it out:

M31 Fidelity vs N ants

OK, this is the M31 model image (ie, dominated by extended structure), with thermal noise limiting the dynamic range to 1000:1 (hey, a 4 hour continuum integration at 300 GHz led to a thermal noise of 8 uJy, so this is a source with peak flux of 8 mJy!) and the integration time has been adjusted so the theoretical thermal noise is the same for all array configurations. The configs with different N ants were optimized by Boone's algorithm, but with an inner core of 11 antennas fixed to give good coverage for the inner 300m. Fidelity is calculated for all pixels brighter than 0.01 of the peak reconstructed image. Fidelity vs N ants is plotted for both MEM (open symbols) and CLEAN (solid symbols). Size DOES matter.

Here's another similar result for the M51 model (dominated by compact features), with thermal noise limiting us to 3000:1 SNR (ie, a 24 mJy source):

M51 Fidelity vs N ants

Other topics:

More on imaging: we (ie, I) need to do a study of multi-configuration imaging with ALMA. IE, how should we do the observing strategies (how much time in each configuration) and imaging strategies (reweighting, perhaps multi-scale methods). THEN, the multi-configuration imaging can be compared with single configuration imaging. FOR EXAMPLE: IF we have to make do with N ants << 64, we may be in a regime where we need to do multiconfiguration observing/imaging routinely, and we should have some detailed understanding for addressing any tradeoffs.

As to configuration redesign, I prefer option C: redesign the entire set of configurations for 50 (or whatever #) elements.

As to site testing: the NRAO container needs NEW BATTERIES or we need to put the NRAO container to bed for the night - at least until we can bring things back to life with electricity from power cables.

As to dynamic scheduling & site testing: some 5% of the time (more like 15% of the time in November 2004) the 11.2 GHz Site Testing Interferometer (STI) is dominated by ionospheric phase fluctuations. Hence, during those times, we will not be able to utilize the STI to help us select the project to observe. We could (1) ignore this as it is usually only 5%, (2) recognize when it is happening and apply the most recent valid phase measurement, (3) use the two WVR units to determine phase conditions, or (4) point one interferometer over the Atlantic and one over the Pacific so we will usually have some valid information from at least one. I favor (3).

-- MarkHoldaway - 14 Feb 2005

L.-A. Nyman -- Site Characterization

The meteorological instruments group was to define the 'ancillary devices'; the current draft of that is in almaedm at: The second task was to define the interface of the ancillary devices to the site. The current draft of that document is in almaedm at:

There has been a lot of email traffic on the first document but I don't know of a new draft. It has been necessary to assume some things to construct the rebaselined Science IPT plan. will summarize the plan which I will submit.

We now own four 'weather stations' on the site. There is one at the ATF. A reasonable plan seems to me to be: Relocate one station to the OSF as soon as that structure is capable of accepting us. That is known as the beneficial occupancy date. That date is currently: 2007 June 5 Beneficial occupancy of the OSF That's too late for my liking but that is what the PMCS guy tells me. I therefore have that date in the plan as the date to establish a weather station at the OSF for use in testing of the first antennas.

The current date for the AOS is 2006 Dec 6. At the telecon Monday we discussed the possibility that that date might slip a few months. That is the date on which the current site characterization equipment will begin the migration to the AOS (or be junked). Certainly we will want to establish the first weather station at the compact configuration at this time.

After that we will deploy the remaining items--weather stations, interferometer(s), lightning detectors, etc. The cameras will go to the system IPT for use in security monitoring of the site. Will we launch the radiosondes during ALMA operation? It would be useful to develop a new 1.3mm tipper but I think this needs to wait for ALMA operations. I don't know about the 183 GHz tippers--opinions? Simon is interested in the submillimeter tippers I believe. Site characterization as a Science IPT activity ends with the end of 2007.

What should be the status of the seismometer?

New equipment includes the thermal profiler in the oxygen line and an infrared camera. It appears to me that the profiler will fit within our current M&S budget, which I am rearranging to accommodate it. When? We can reasonably expect to use the array for real science verification when there are three antennas on Chajnantor. In the current Plan this occurs in March 2009. I think we should plan on the purchase and installation of this device during 2008, after redeployment of the other devices. I think that the IR camera also fits within the budget. I have put that as last for deployment.

Discussion on this would be welcome. I think it is appropriate to try to decide some of these things before the calibration meeting tomorrow, and to discuss the decisions at the Science IPT meeting next Tuesday. Therebaselining plan is due last week and will be submitted asap.

- AlWootten - 14 Feb 2005

Science Corner:

Upcoming Meetings

Dusty and Molecular Universe 27-29 October 2004, Paris Presentations Online

2005 IEEE International Conference on Acoustics, Speech, and Signal Processing March 19-23 2005, Philadelphia See

Radio Astronomy Session; ALMA Article for ICASSP. Comments? Reviews welcomed.

IAU Symposium 227 Massive Star Birth: A Crossroads of Astrophysics May 16-20 2005, Acireale, Italy

Workshop on submillimeter wavelength astronomy in Cambridge (JUN 13-16).

Astrochemistry throughout the Universe: Recent Successes and Current Challenges 2005 August 29 - September 2; Asilomar, California

Protostars and Planets V 24 - 28 October 2005 Hilton Waikoloa Village, The Big Island, Hawaii

URSI General Assembly 23-29 October 2005; New Delhi, India; "Mm/submm Techniques and Science" session 25-26 Oct.

-- AlWootten - 11 Feb 2005
Topic revision: r6 - 2010-08-03, ToddHunter
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback