MMA Imaging and Calibration Group

Agenda for meeting Mon, 26 April 1999 at 4pm EDT.

Date: 26 April 1999

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

Agenda

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Holography PDR Meeting - Mangum, Butler

We will discuss items arising at the this meeting on 19 April 99. --------

News; October Meeting - Wootten

Division Heads meeting stuff. Bob was interested in progress on configurations.

Sargent, Boss, Scoville, Crutcher, Spergel, Millar, Jewitt and Evans have accepted our invitation to speak. Hartmann will be at a conference in the Canaries but suggested his co-worker Nuria. Steve Beckwith is involved in the ST refurbishment mission and cannot attend. I suggest Koerner as a replacement--other suggestions before I pass this along to the SOC? Boss pointed outthat this is: ' a chance for the CIW to showcase a field that DTM helped establish through Merle Tuve's neutral hydrogen surveys and Bernie Burke's pioneering studies. I just alerted the CIW editor about the conference, and suggested that she prepare a display poster highlighting the DTM/CIW linkage, which she seemed to think was a good idea, so maybe that will do the job! ' I wasn't fully aware of this history.

Harvey is back from IRAM, he may have interesting news.

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M51 Far, far away -- Yun

Min's simulation of M51 Long, long ago will be discussed when he returns.

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BIMA MDC Report -- Wootten, from Blitz

antenna design group - Matt Fleming investigated antenna drive systems and azimuth bearings and seals for the antenna design group, and participated in design review meetings. He is working on an MMA memo discussing friction drives.

22 GHz water vapor radiometer - At Maryland, Andy Harris and Johannes Staguhn finished construction of the first analog correlator module, which will be tested at Owens Valley in June. They are putting together a flexible software package to test various phase recovery algorithms, both at 22 GHz and at 183 GHz. At Berkeley, Dick Plambeck has done a preliminary design of the 22 GHz coupling optics; the goal is to illuminate the subreflector with less than 2% spillover, to make certain that the 22 GHz beam is not picking up water emission from far off-axis.

amplitude calibration - Douglas Bock, Jack Welch, and Matt Fleming installed the amplitude calibration hardware on the subreflector of antenna 6 in Dec 1998. The associated control hardware and software is complete and integrated into the existing observing systems. The rotating mirror arrangement has proved reliable throughout the winter, during which it was operated regularly during observations. The temperature of the loads was maintained to within a few tenths of a degree. The coupling of the calibration system to the main beam has been measured over a range of wavelengths in the 1mm and 3mm bands. The next step is to use the new hardware for everyday observations to gauge its effectiveness.

MDC Networked Telescope Project - The development team at NCSA/UIUC Astronomy is currently made up of Raymond Plante, Dave Mehringer, Doug Roberts, and Mark Gates; only Dave Mehringer is (partially) funded by NRAO. Progress since fall 98 has been characterized primarily by architecture design. After a basic framework was developed, we held our first design workshop on January 14, 1999 which brought us together with a variety of consultants from NCSA and its partners to address specific design issues (for more details, see http://monet.astro.uiuc.edu/DataArchives/wkshp1.html). We expect that the basic design for the archiving and metadata management subsystems to be completed by spring 99; this will result in a general design document. Our design is based on a holistic model that tracks the life of a project from proposal to publication. Major features of the design include distributed archives for storing data and distributed compute machines for processing it. Important design choices adopted thus far include the Globus tool kit (http://www.globus.org) for managing distributed resources and XML as a metadata interchange format. Besides participating in the system design, Mehringer has begun work on tool development. He recently completed a beta version of DaRT, a flexible and user-friendly tool for retrieving data from an archive. This is currently under going friendly user testing by users of the BIMA archive.

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OVRO MDC Report - Wootten, from Sargent

Work for MMA project at OVRO

March 1, 1999

I. Antenna design work

A major part of the OVRO effort (specifically involving David Woody and James Lamb) has been in the area of antenna design for the MMA. The novel OVRO design has been refined and its performance under a variety of load conditions has been analyzed. The structural model of whole telescope was used for this analysis. The results indicate that the design is a viable solution for the MMA. At least one antenna vendor is actively pursuing this design for its bid for construction of the MMA prototype. The final report on this 10-m design is now almost complete [4].

Both Woody and Lamb participated actively in the discussion of the optimal antenna diameter for the MMA/LSA. To this end two written evaluations of the antenna design issues were provided to NRAO and a presentation was made at the November 1998 meeting of the Millimeter Array Advisory Committee (MAC). Preliminary scaling of the OVRO design to 12-m has been carried out and a few load cases analyzed to verify that the design can be successfully scaled to 12-m.

A full analysis of the thermal measurements of the Leighton 10-m antenna backing structure has been completed [1]. This gives sufficient data for evaluating MMA antenna designs which use similar geometries. It will serve as the baseline for the antenna vendors in evaluating the thermal performance. Some further work has been done to understand the thermal behavior of the proposed panels. This includes extensive measurements of a test panel and numerical modeling.

Woody and Lamb also worked on the evaluation of the prototype antenna RFP. This involved detailed analysis of contributions to the specifications (e.g., [3]). The antenna drive control will be difficult and we worked on refining how to present this requirement in the RFP. Steven Scott of OVRO also worked with the real-time computing group at NRAO to help define the software interface to the antenna.

II. Optical layout work

We have made a detailed study of the optical layout for the MMA 12-m antenna design. Losses due to aberrations from offset feeds, and secondary mirror notation were quantified. The trade-offs of the various geometrical parameters (particularly secondary mirror diameter) due to diffraction, blockage and aberrations have been studied and an optimum geometry recommended. A detailed analysis of the effect of specifications for the nutating secondary on the mechanical drive requirements was also carried out.

Some progress has been made in the optics for the MMA receivers. A preliminary investigation of an illumination shaping scheme has been carried out, but not yet written up. It explores some of the trade-offs between the improvements of the antenna efficiency and the losses and complexity of the added components.

III. Water Line Monitor

Most of the work during the last quarter has been in the area of improving the accessibility of the WLM data to the astronomer. The data are now automatically transferred to the data base. Some simple tools are available for the astronomers to evaluate the WLM to phase correlation, but it remains to finish the implementation of useful astronomy data correction algorithms.

The hardware progress has been mainly in the area of improving the reliability of the WLM systems. The down time is now much less than 1%. The design of the next generation cooled WLM was delayed by the extensive antenna design effort described above.

A technique for determining the altitude of the atmospheric delay fluctuations has been tested. The altitude of the fluctuations is important for evaluating the efficacy of different phase correction schemes. It was previously shown that the cross-correlation of the WLM signals with the telescopes pointed at the zenith can be used to determine the pattern speed for the fluctuations. The new technique involves pointing the telescopes at a common point ~2 km above ground. A comparison of cross-correlation for these two cases then reveals the altitude of the turbulence. For example, if the turbulence is at 2 km then all of the WLMs will have a peak correlation at dt=0. We discovered that in some conditions the turbulence is in one dominant layer close to 2 km but at other times there are two or more important layers. We will continue to refine this technique in the coming year.

[1] Thermal behavior of the Leighton 10-m antenna backing structure, J W Lamb and D P Woody, MMA Memo. 234, October 1998.

[2] Optimized Optical Layout for MMA 12-m Antennas, J W Lamb , MMA Memo. 246, January 1999.

[3] Secondary mirror positioning tolerances, J W Lamb, Internal note, January 1999.

[4] "A Design for a Precision 10-m Sub-Millimeter Antenna," Woody and Lamb, MMA Memo ?, Feb. 1999.

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22/183 GHz meeting plans - Ensemble

How does 7 June sound?

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Correlator Dumptime - Rupen

If he has had time, Michael will lead a discussion of how the upscoping of the array affects the discussion in his memo No. 194 .

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Total Power Mapping --'Holdaway Holdover' Memo - Butler

  • We will discuss Holdaway's Protomemo (postscript) on total power mapping. ----------------------------------------------------------------------

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    Action Items 26Apr99

    UPCOMING REVIEW: On 7 June (?) 1999 we review results from the OVRO and BIMA phase correction systems.

    DECISION: Congfigurations--where are we? DECISION: 183 GHz or 22 GHz phase correction?

    DECISION: Is a nutating secondary necessary?

    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?

    MEETINGS: Holography PDR 19 April MEETINGS: MOC meeting 12-13 May 1999, Tucson. MEETINGS: MAC meeting 19 May 1999 at noon. ------

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    Travel

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    T. Helfer:

    A. Wootten: 28 May - 3 Jun AAS 5-9 Jun I99 9 - 18 Jun CSO 19 - 30 Jun Japan.

    J. Mangum:

    M. Yun: AtCSO this week.

    B. Butler:

    S. Radford: