Minutes for meeting Mon, 26 July 1999 at 4pm EDT.
Date: 26 July 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
Minutes
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Chuck Broadwell has posed a science question for the correlator. At the moment, when you are operating some part of the array in autocorrelation mode, it appears difficult to provide the increased number of frequency channels you get in cross-correlation mode. That is, in cross-correlation every time you cut the bandwidth in half, you also double the number of frequency channels so that the frequency resolution is improved by a factor of four. For autocorrelation, the total number of frequency channels in a given mode would remain fixed, so that resolution would improve only by a factor of two when the bandwidth is cut in half. This restriction makes it possible to operate one subarray doing single-dish mapping while the remainder of the array runs in interferometric mode. Is this restriction acceptable from the science standpoint?
The MMA ImCal group discussed this on 26 July. This restriction may require some observations to be taken in an over-resolved mode, with the data smoothed in software later. We could not identify a reason why this would not be scientifically acceptable.
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See my notes emailed separately. The strawman configuration which Tamara and Simon have devised since the Tucson meeting will be discussed as a prelude to its presentation to the MAC on Wednesday and discussion at the URSI meeting next month.
Simon and Tamara will compare the 64 element optimizations Leonia has performed and match these to existing site maps to produce a strawperson layout similar to that produced for the MMA Reference Design. The results were plotted for that 36 10m antenna design. The circles at the antenna positions are not to scale, but provide leeway for topography, etc.. Leonia's optimizations for the B, C and D arrays should be easy to mate to the site, but those for the A array and the 10km array will be more difficult, owing to incompleteness in the terrain maps in some regions.
The question of whether it is operationally desirable to have a crew committed to moving antennas always will be discussed at the 2 Aug DH meeting.
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See my notes emailed separately and since updated. Someone has changed the decision date to 1 August. Al will circulate a list of pros and cons for recommending that we adapt 183 GHz as the baseline plan for water vapor radiometry.
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Update on URSI: There will be a 17 Aug meeting with the European DHs at URSI. Kawabe has circulated a tentative agenda for the 14 August workshop. Mangum will speak on amplitude calibration of the MMA. Yun will speak on the strawperson configuration. Radford will give a short presentation on future site testing. Wootten suggested other topics to be covered might include:
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This coming Weds at the usual time. We will discuss the audit. We need to obtain last inputs on the WVR decision due next Monday and on the descope options (Q band, combining 3mm bands into one) which the Audit committee proposed. It might be possible to get the impossible eleven bands currently designated for the dewar down through two descoping means: 1) eliminate 7mm or 2) combine the two 3mm bands into one 70-116 GHz band. A sizable chunk of science would be lost from option 1), which Carlstrom is writing a report on. However, some engineers and a contingent of the ESO partners favor this option. Little would be lost from option 2), however, but there is concern about a) loss of sensitivity at band extremes, owing to uncertain performance of the OMT--Wollack will investigate this; b) 1/f noise in the HFET which would presumably be necessary to cover this band; and c) broadband first mixer for that HFET which is not currently available. At the moment the best plan seems to be to ask the receiver group to evaluate factors a, b and c, as option 2) might be preferable to option 1). BIMA currently covers the band 70-116 GHz in a single polarization with narrowband SIS devices. Also we will discuss data rates and the image library.
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The data rate figure I've been carrying in the project book is 1MB/s average, 10MB/s max sustained. This comes from the Scott et. al. memo (#164) which in turn apparently came from a Tucson science meeting (40 antennas). Mark Holdaway should know about this number. Rupen in a later memo comes up with a science case for 100's of MB/s (OTF synthesis surveys). Note that the NRAO correlator design is capable of dumping data from the LTA at a rate of 1GB/s.
This topic will be revisited next week. Brian noted that according to Escoffier, the correlator design can be upgraded to dump 16 GB/s. What is the science-driven rate?
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I will update everyone on the status of this event.
Estimate of number of attendees:
32 members of SOC (includes MAC members)
5 members of LOC (not included above)
28 non-MAC speakers
50 WWW registrants (some overlap with above)
Estimate about 120-130 registered attendees. Auditorium holds 400.
Estimate ~ 50 poster papers. Posters in reception hall, 57 x 29 feet.
At this time, seven people have paid registration fees, and seven people have reserved a room.
Lodging will be covered by each individual attending the conference. AUI has a contract with the Omni-Shoreham, which will provide these at a reduced rate of $149. This block of rooms is released on 9/12/99, after which rooms will be available for space available at prevailing rates.
Rental of Carnegie will be (has been?) negotiated with CIW Treasurer/ AUI Trustee Lively. Detailed cost unknown to HAW or PvB.
House science reception to be covered by AUI and registration. Provisions provided by House caterer. Room holds 50 people seated, 75-100 standing. This reception will be by invitation only owing to space constraints.
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Progress is slow owing to a lack of suitable simulation software. We discussed a) breaking the memo up into parts describing 1) Noise in e.g. EKH chopped and restored maps and 2) Noise in OTF maps. A qualitative description with numbers can be prepared for the project book, which aleady has 1/f noise constraints in a table.
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DECISION: Configurations--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: MAC meeting 28 July 1999 at noon. ------
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T. Helfer: 13-17 July AOC Imaging meeting.
A. Wootten: 14-25 July Vacation, 13-19 Aug URSI.
J. Mangum:
M. Yun:
B. Butler: Baby leave.
S. Radford: