Minutes for meeting Mon, 13 September 1999 at 4pm EDT.
Date: 13 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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I calculated new 'standard' ALMA sensitivity numbers. Please comment upon these. You may find them at ALMA Sensitivities .
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I think we need to extend the work Tamara began on simulating ALMA images to (1) reproduce it, and (2) include single antenna data to determine the effect that has on the sidelobes. Tamara continues to work on this as time permits.
Min put his URSI talk into html format. We will take a look and give Min some feedback.
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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
0900 Committee Caucus
Overview of the Project at Midcourse -- R. Brown
Antenna Procurement Contract -- P. Napier, Anderson(?)
Other Technical Reports
Report on LO PDR -- as appropriate
ALMA Frequncy Bands -- Wootten
Science updated -- Wootten
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 -- Churchwell, Menten
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Now for the MAC meeting this week. Items we should discuss:
1) Science with the Atacama Large Millimeter Array
Meeting status, SOC matters.
2) October MAC meeting
3) Action list
a) A plan for deploying the remainder of the receivers after the initial three.
Now that we are ALMA, this will be developed in concert with European partners. A meeting will occur in Tucson on 30 September. Recall that a joint WBS should be in place on or soon after 10 October 1999 to be ratified at the next meeting of the ACC.
c) Phase Calibration-necessity for fast switching and implications for hardware; water vapor monitoring- 22 GHz vs 183 GHz lines.
John Carpenter put together some pages on his URSI talk on what is happening at OVRO; a link to these may be found at our ImCal WWW page.
d) Total Power Observations-requirements for receiver stability, 1/f noise, necessity for a chopping secondary, etc.
This was discussed at URSI but there have been no developments since the URSI discussion last month.
e) Array Configurations-what are the most useful configurations, especially the most compact ones? We need to understand the pros and cons better.
Min presented the U. S. strawman plan at the URSI meeting and has written this up in his WWW page.
f) OFT Mapping, Focal Plane Arrays, etc.-we need to try to understand how often these are likely to be used and their implications for both software and hardware.
Issues of maximum data rate and minimum dump time will be revisited in the next Imaging and Calibration meeting. In the project book this is 1MB/s average, 10MB/s max sustained, numbers derived from the 40 x 8m array. Currently. minimum integration time is 16 ms for cross-corretations and 1 ms for autocorrelations.
g) Testing of the Prototype Telescopes-Where, how long, and what criteria for acceptance?
The plan for prototype testing is being finalized and is due on 27 September 1999. Note that the first production telescope may differ.
h) Someone to fill the role of Mark Holdaway-It seems like the project needs someone doing the type of things Mark was doing for the project.
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As long as the 90 GHz channel is in use, it might be useful to have it continuously tuned. How often will one want to use it (or the WVR system)? We will want to use it whenever the instrument is not 'phase stable'. We have defined at one point 'phase stable' as better than a radian, and at another, in the goals listed in the project book, 0.15 radian at 230 GHz. D'Addario has proposed updating these:
Darrel pointed out that 1) is very hard but probably the right goal. 2) comes to 5 microns of path length, which is probably not possible. Perhaps the goal might be 0.3 radian; but that is still very difficult. We will discuss this at the 13 Sept. Imaging and Calibration phone meeting. For the moment, let's take the more stringent project book specification (acknowledging that Larry's is more stringent yet). What do we know of the site?
For the project book goal, we reach 99% of theoretical sensitivity. Without any corrections, we achieve this 30% of the time on 150m baselines, and 1% of the time on 1.5km baselines, according to MMA Memo No. 169. If we only want 50% sensitivity, this is achieved 85% of the time on the shorter baseline and 43% on the longer baseline. For 90% sensitivity, the percentages are 60% and 12%. If we assume that we are thinking of 230 GHz, I would say that fast switching/WVR system will NOT make a significant improvement only 1% of the time at kilometer baselines, and will be used for all observations on those scales. In the compact array, I would say that the WVR system would NOT make a significant improvement perhaps 40% of the time, and would be used just over half of the time. I would conclude that for the average observation at 230 GHz or above, in whatever array, the WVR system or fast switching will be in use. Below 230 GHz in the compact arrays, it might not make a significant improvement in most cases.
If we were to assume that the compact configuration will be used say 25% of the time, this suggests that we will use fast switching or WVR almost all of the time. The 3mm system will nearly always be in use for fast switching, unless the WVR system works so well it is not needed. At the moment, I don't think we can say. Th most conservative course of action, it seems, would be to plan to have the 90 GHz channel on almost all of the time.
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I will update everyone on the status of this event.
Registered: 163 (-2 cancellations)
Paid: 109
Banquet: 100
Kate has posted these to the WWW. I will order posterboards enough for 60 posters.
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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.
What is the science-driven rate?
Here are the spectral channels/bandwidth values for the prototype LTA. The
minimum integration time is 16 ms for cross-corretations & 1 ms for
auto-correlations
(i.e., there is no time/spectral channel trade off as in earlier designs)
Mode Spectral Baseband Baseband
Channels Bandwidth Bandwidth
not oversampled oversampled
0 512 2 GHz 1 GHz
1 1024 1 GHz 500 MHz
2 2048 500 MHz 250 MHz
3 4096 250 MHz 125 MHz
4 8192 125 MHz 62.5 MHz
5 16384 62.5 MHz na --------
What science will be lost if we have three or fewer subarrays? --------
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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 15 September 1999 at noon. Next ImCal meeting 13 September 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:
J. Mangum:
M. Yun:
B. Butler:
S. Radford: