2005-02-10 ALMA Calibration Group Telecon Agenda and Minutes
Table of Contents:
ALMA Calibration Group Telecon |
- Date: February 10, 2005 (Thursday)
- Time: 16:00 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
| Assigned To || Due Date || Description || State || Notify || |
Agenda and Minutes
NOTE: Discussion from the telecon is shown in italic.
- Matt Carter
- Richard Hills
- Jack Welch
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.
Before this telecon it was suggested that we discuss issues related to the following three calibration categories:
- 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
- Amplitude and Flux Calibration (Welch)
- See relevant discussion in Phase Calibration section next.
- Phase Calibration (Hills)
- Richard Hills (submitted via email before the telecon): Clearly there are many aspects of Phase Calibration which relate to the hardware - the LO and IF stability, including things like the problem of the fibre twisting at the telescope axes, are obvious ones. I assume however that we are concentrating on the Correction of the Atmospheric Phase. This is of course all about what is going on in the atmosphere - temperature, pressure, humidity, turbulence and wind are all involved. The same factors are clearly relevant to Amplitude Calibration (correcting for the atmospheric losses), Pointing (refraction corrections), Antenna Location (ditto) and perhaps other topics (Bandpass?). So from this perspective the question is, "What specific information is needed about the atmosphere in these various areas and to what accuracy, resolution, at what locations within the site, etc?"
- All: Agreed that an atmospheric temperature sounder (oxygen sounder) was essential for WVR phase correction.
- JimGibson and Jack Welch: Atmospheric temperature sounder is needed for the amplitude calibration system also.
- Richard Hills (via email): On a narrower point, do any of these other areas, especially the Amplitude Calibration, need the values from the water vapour radiometers on the individual antennas? I can't think of any information that flows in the other direction - i.e. is needed by the Phase Calibration from the Amplitude of Bandpass Calibration activities, although I suppose that in principle these might be used to give an indication of the presence of clouds if the right combination of frequencies were being used. Can anyone point out anything important?
- Jack Welch: Even though WVR information on content of the LOS water vapour is not essential to the amplitude calibration system (for absorption calculation), it could be useful. Depends in the end on how accurate these measurements are in relation to a good atmospheric model predication of these same quantities.
- RobertLucas: Can't get an accurate enough Tatm from WVR for amplitude calibration system.
- Richard Hills (via email): Let me just point to one which is of concern to us at the moment. What is a reasonable plan for testing the phase calibration concepts and when does it need to take place relative to finalizing designs and making manufacturing commitments? The problem is that the availability of the ATF for interferometric testing seems to have moved off into at least 2006 (and for dry weather conditions maybe even until fall 2006) and we have to decide whether to organise something else in the interim. If so what?
Lets try again to discuss Bandpass Calibration at our next telecon.
- Bandpass Calibration (Guilloteau)
- No discussion on this topic.
Amplitude Calibration Subsystem Development Reports
- Berkeley Absolute Flux Calibration System (JimGibson/Welch)
- Data reduction continues. Large amount of data to analyze. Stalled by the need to measure the millimeter loss in waveguide.
- Semi-Transparent Vane (STV) Calibration System (ThomasWilson)
- The contract for finishing lab tests of the S/T vane is still being negotiated with the laboratory in Madrid. Still hope to have this done by the end of February 2005. At that point we should have a meeting to determine which amplitude calibration scheme is to be used.
- Multi-Load (ML) Calibration System (Matt Carter)
- RAL-built calibration load should be sent back to Grenoble next week.
- 90 GHz measurements will start next week.
- Test measurement results may be available at next telecon (one month)
| Assigned to || Due date || Description || State || Notify || |
| ThomasWilson, Main.Martin-Pintado || 2005-02-22 || Produce a document on the results of ST vane measurements (with Jesus Martin-Pintado). This should include a discussion of the related limits on receiver saturation. || closed || ThomasWilson || edit |
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
- All: Unanimity regarding the need for a temperature sounder. As this device has not received the attention within the upper echelons of the ALMA Project, the necessity of this device needs to be emphasized wherever possible.
- AlWootten pointed out that we need to finish the Ancilliary Calibration Device Specification and the ICD for those devices between Science and Site. JohnRicher will update this specification and submit to AlWootten by 2005-02-17.
The revised Ancilliary Calibration Device Specification will include, among other things:
- Weather station (pressure, temperature, humidity) layout. Default plan is to place 4 towers in a Y-configuration over AOS site. There will also be one at the OSF.
- 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
| Assigned to || Due date || Description || State || Notify || |
| JohnRicher || 2005-04-15 || Circulate revised Ancilliary Calibration Devices document for comment by the ALMA Cal group. || closed || JohnRicher || edit |
Once this specification is submitted, JeffMangum
will consult with the Antenna IPT regarding the requirements for windbirds on or atmospheric monitors near the antennas.
Date of Next Phone Meeting
The next ALMA Calibration Group telecon will be 2005, March 10th 16:00 UT
. This is our "normal" meeting time (16:00 UT on the second thursday of each month).
- 10 Feb 2005