2004-12-09 ALMA Calibration Group Telecon Agenda and Minutes
Table of Contents:
ALMA Calibration Group Telecon |
- Date: December 9, 2004 (Thursday)
- Time: 17:00 UT
- Duration: 1.0 hr
- USA Toll Free Number: 1-877-919-7148
- International: +1-203-566-1039
- Passcode: 5 1 0 4 6 8
- Leader: JeffMangum
Action Items from Last Telecon
Agenda and Minutes
NOTE: Discussion from the telecon is shown in italic.
- Richard Hills
Thanks to those who contributed to the recent significant revision to the Calibration Plan
. More work needs to be done on this document before it can be considered "done". Recall that we have organized ourselves into small groups concentrate on specific sections of the plan. I list below these groups, with the "lead volunteer" denoted in bold:
With regards the updates to the individual Calibration Plan chapters, with the exception of the changes identified through the Action Items, the Calibration Plan appears to be in pretty good shape.
All group members should read through the current version of the plan and suggest changes.
- Amplitude and Flux Calibration (Welch, Butler, Carter, Gibson, Holdaway, Mangum, Martin-Pintado, Kawabe, Wilson)
- Phase Calibration (Hills, Holdaway, Mundy, Richer, Stirling, Wootten)
- Bandpass Calibration (Guilloteau, Bacmann)
- Polarization Calibration (Myers, Holdaway, Laing)
- Pointing Calibration (Mangum, Lucas, Holdaway)
- Antenna Location Calibration (Conway, Wright, Morita)
- Antenna and Electronic Delay Calibration (Lucas)
- Optics Calibration (Butler, Saito)
- Total Power Calibration (Holdaway, Mangum, Mundy, Kawabe)
- Primary Beam Calibration (Holdaway, Wilson)
- Archiving and Accessing Calibration Quantities (Lucas, Mangum)
Calibration Category Issues
The following is a list of "calibration categories" which JeffMangum
suggests we should discuss on a regular basis (note the similarity to the Calibration Plan sections). Please suggest additions/deletions to the following list.
We had planned to discuss issues related to the following three calibration categories at the 2004-11-09 and 2004-12-09 telecons:
- Amplitude and Flux Calibration
- Phase Calibration
- Bandpass Calibration
- Polarization Calibration
- Pointing Calibration
- Antenna Location Calibration
- Antenna and Electronic Delay Calibration
- Optics Calibration
- Total Power Calibration
- Primary Beam Calibration
- Archiving and Accessing Calibration Quantities
No discussion topics were discussed. The calibration category leads (indicated in bold) will suggest topics of discussion within these three categories by 2005-01-13.
JeffMangum suggests that "interconnections" might be a good topic of discussion for each of these three calibration categories at our next telecon.
- Amplitude and Flux Calibration (Welch)
- Phase Calibration (Hills)
- Bandpass Calibration (Guilloteau)
Amplitude Calibration Subsystem Development Reports
- Berkeley Absolute Flux Calibration System (JimGibson/Welch)
- No new results. Will have results at next telecon.
- Semi-Transparent Vane (STV) Calibration System (ThomasWilson)
- The contract for finishing lab tests of the S/T vane are now in at ESO and sent to Madrid. I plan to have this done by end Feb 05, and then we have a meeting to determine which amplitude calibration scheme is to be used.
- Multi-Load (ML) Calibration System (ThomasWilson)
Weather (Ancilliary) Measurement Devices
At the 2004-11-09
started a discussion of the state of the "ancilliary" measurement devices (generally, weather measurement devices). AlWootten
pointed out that the Project will soon go through a "rebaselining" exercise, which will involve a reorganization of the scope of the Project. Since ancilliary devices are not currently funded, we need to make the case for the necessary ancilliary devices now
. Jack Welch suggested that an oxygen sounder would be very useful to have. AlisonStirling
has posted her review of oxygen sounders to the CalAncillary
pointed out that we need to finish the Ancilliary Calibration Device ICD between Science and Site. AlisonStirling
will update this ICD and submit to AlWootten
This revised ICD will include, among other things:
- Weather station (pressure, temperature, humidity) layout. Default plan is to place 4 towers in a Y-configuration over site.
- A relaxed specification for the hygrometer. Neither the refraction calculation nor the baseline determination requirement calls for better than 1-2% absolute accuracy. See CalLoc for a discussion, including pointers to JohnConway's ALMA Memo (503; see CalLocMemo) on antenna location calibration for details
Once this ICD is submitted, JeffMangum
will consult with the Antenna IPT regarding the requirements for a windbird on the antennas.
| Assigned to || Due date || Description || State || Notify || |
| JeffMangum || 2006-09-01 || Consult with Antenna IPT regarding windbirds mounted to production antennas. || closed || JeffMangum || edit |
Antenna Location Calibration News
Even though he was not able to attend the telecon, JohnConway
reports that he is working on a revised version, which incorporates reviewer comments, of memo 503. The changes in this version are mostly minor; the one that is critical to the project concerns discussion and specification of the instrumental delay versus large angle (e.g 180 deg) slews. In Memo 503 JohnConway
had assumed that this would not be a problem, the technical spec I was working to implied that it would be only slightly larger than the variation in instrumental delay over 2 deg. Memo 503
made people aware that instrumental delay error stability over large angles was an issue (i.e. emails to JohnConway
from D. Emerson at the start of November).
has attempted to contact Bill Shillue to suggest that
we start negotiating a joint change request. Obviously its important to get to the bottom of this, if we can't calibrate antenna positions quickly the concept of continuous reconfiguation may be untenable, and if its really bad
we may not be able to find our antennas at all to high accuracy even in conventional burst reconfiguration.
Looking a Craig Walkers excellent comments on my memo, its clear that in geodetic VLBI active measuremnt of instrumental delay by injection of phase cal tones at the front end and detection of phase vs freq is vital to achieve millimeter accuracies. We are of course trying to achieve 10 times that accuracy without such a system. If there are doubts about whether the instrumental delay stability we require for antenna position determination are posible, such a scheme might have to be considered, and worked on as a backup. (and would also be useful for removing instrumental contribution in conventional fast switching over 2 deg).
The LO distribution stability is one of the critical items for development in the whole project.
Date of Next Phone Meeting
The next ALMA Calibration Group telecon will be 2005, January 13th 16:00 UT
. This is our "normal" meeting time (16:00 UT on the second thursday of each month).
- 09 Dec 2004