Minutes for meeting Mon, 27 September 1999 at 4pm EDT.
Date: 27 September 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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The project book data rate is 1MB/s average, 10MB/s max sustained. This comes from the Scott et. al. memo (#164)</a> which in turn apparently came from a Tucson science meeting (40 antennas). Rupen in a later memo (#194) comes up with a science case for 100's of MB/s (OTF synthesis surveys). In Memo #192, Rupen discussed some science issues which may drive data sampling parameters. Note that the NRAO correlator design is capable of dumping data from the
LTA at a rate of 1GB/s. What is the science-driven rate?
The science requirement which most drives this is:
Wide Field of View
- Mosaicing capability (fast moti
- Total power capability (fast motion)
- Compact array configuration
- Precision amplitude and phase calibration (fast switching)
- Fast correlator dump times -- High data rates
Fast Integration
- Solar observations (bandwidth can be reduced as sensitivity is not an issue
- Pulsar observations (array may be phased)
Since the issue was last considered, the number of antennas has increased to 64(though 50 is a
more realistic number) and the diameter has increased to 12m. Since the number of baselines has
gone up by a factor of 2.6, the average and peak datarates should be increased by at least this
number. An increase in antenna diameter decreases the beamsize and therefore affects the rate at
which a large field of view may be imaged. As Rupen points out in Memo No. 192, this rate
goes with the square of antenna diameter, and so for the simplest case requires sampling at rate
2.25 times faster for 12m antennas than was required for 8m antennas. The maximum sampling
rate is now 1 ms for autocorrelation data, and 16 ms for cross-correlation data. Rupen (192)
suggested that dump times of 40 (D/8m)-2 were desirable. The increase in antenna diameter has
left the rates within the nominal range.
What are the datarates which these dump times correspond to? Rupen shows that at the fastest
rate the antennas can be driven, a rate set by the necessity to be able to suppress atmospheric
fluctuations, the integration times may be as short as one millisec for a 12m antenna at the
highest range of operating frequency, 850 Ghz. This results in a datarate of 1000*256 spectral
channels*4bytes per datum*64 antennas or perhaps 65 MB per second, about twice times the
project book standard scaled to 64 antennas. One could choose to cut this by compromising e.g.
the number of channels, the degree of atmospheric cancellation (perhaps by observing only in the
best weather), or by observing with a subarray (in the case where this might provide the requisite
sensitivity).
The conclusion was reached by the discussion group that the datarates should be modified upward to:
30 Mbytes/s Maximum sustained data rate
3 Mbytes/s Average raw data rate
Barry Clark opined that today one could get off-the-shelf hardware which could accomplish 10 Mbytes/s; while 30 Mbytes/s was probably the maximum achievable.
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Comments on MMA Memo No. 274.
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So here is a possible agenda for the 9 October meeting.
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ALMA Science Advisory Committee
9 October 1999
Agenda
Omni Shoreham Hotel meeting room reserved, setup in school room style.
Provisional estimate: 70 attendees, maximum.
'Freshly brewed coffee, tea, hot chocolate' $47 per gallon
'Mineral water' $6 per liter
'Muffins' Blueberry, Orange cranberry, , Banana $30 per dozen
0900 Committee Caucus
Overview of the Project at Midcourse -- R. Brown
Antenna Procurement Contract -- P. Napier, Anderson(?)
1030 Coffee 'Freshly brewed coffee, tea, hot chocolate' $47 per gallon
Other Technical Reports
Report on LO PDR? -- as appropriate
ALMA Frequency Bands -- Wootten, Guilloteau
Long baselines -- Wootten, Guilloteau
Science updated -- Wootten, Guilloteau
1200 Lunch (hotel charges begin at $25 per person; perhaps eat out?)
Blueprint for the Joint ALMA Project D&D Phase -- R. Kurz, R. Brown
Definition and Formation of Joint ALMA Science Advisory Committee
-- Wootten, Churchwell,
Guilloteau, Menten
Committee Caucus -- New SAC
1530 Coffee
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Stephane proposed a similar set of goals:
" US-Europe Meeting goals
- Setup a proposal for the joint ALMA SAC (format, suggested names perhaps in a restricted session)
- Discuss timeline differences between Europe and US
- Discuss the 35 GHz band issue
- Discuss the longest baseline issue
- Present and discuss the draft Work Plan which we must have prepared for that date (I'll send you soon a preliminary draft)
- Discuss our position vis-a-vis the Japanese proposals
- Any items you wish
- Any other business
Since most of the scientific topics will have been covered before, I believe we should stick to practical problems."
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I will update everyone on the status of this event.
Registered: 178 (-2 cancellations)
Paid: 132
Banquet: 122
Posters: 59 abstracts received; 72 including intendees.
I've created a posterbook for the meeting. Some pages are not in this version-- participants and paper numbers, for instance.
Kate has posted these to the WWW. I will order posterboards enough for 72 posters.
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| Geoff Blake wrote: Lee Mundy has made a nice image of what ALMA might see in a YSO accretion disk. I think it is quite pretty, and there are lots of features in the image: 1) A central hole 3 AU in radius. 2) A roughly 2AU wide cleared ring centered 7 AU with soft edges -- Lee used a Gaussian in absorption. 3) A protoplanet overdensity at 9 AU with a Gaussian FWHM of 2 AU and a factor of 9 overdensity. The wings are created by a second Gaussian component which is elongated along the orbital path. 4) A protoplanet overdensity at 22 AU with a Gaussian FMWH of 1.5 AU and a factor of 6 overdensity 5) A protoplanet overdensity at 37 AU with a Gaussian FWHM of 3 AU and a factor of 4 overdensity 6) The word ALMA written in the lower part of the disk with an overdensity of a factor of 2 on the underlying disk The leters are 12 pixels wide and 100 pixels high -- that is roughly 4 AU by 35 AU. 7) The word ALMA written in the upper part of the disk with an underdensity of 20 percent. Each of the protoplanets also has an underdensity of 10 percent in a ring at the same orbital radius. The ALMA letters are in there as a gauge of image fidelity. In the ALMA simulated observations, the beam for 10 km baselines at 230 GHz is around 20 milli-arcseconds which is 2.8 AU at Taurus (the pixel size in the model is about 0.35 AU). There is no phase noise in the simulated image, but there is gaussian noise at the level appropriate for the stated ALMA sensitivities. The image really drives home what ALMA can do in planet forming environments. I think we are also going to try and add an envelope to this for very deeply embedded systems, and Michiel Hogerheijde is going to run a 2D Monte Carlo simulation for spectral line work. |
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DECISION: Configurations--where are we?
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 9 October 1999 at 9am, face to face at the Omni, D. C. Next ImCal meeting 4 October 1999. ------
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If your travel isn't on here you have not sent me a travel authorization.
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A. Wootten: 5-9 October, DC
J. Mangum:
M. Yun:
B. Butler:
S. Radford: