2006-05-11 ALMA Calibration Group Telecon Agenda and Minutes
Table of Contents:
ALMA Calibration Group Telecon |
- Date: May 11, 2006 (Thursday)
- Time: 15:00 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.
- Shigehisa Takakuwa
Solar calibration is a subject of some urgency. An example document is being written. Question: Need the nutator be used during solar observing? See also Solar Oberving wiki page.
Information regarding the solar loading performance of the Mitsubishi prototype was presented by BaltasarVilaVilaro. On their Al subreflector over a 30 minute period they measured a temperature increase of 25-30 C above ambient and calculated an absorption coefficient of approximately 15% for the subreflector. The measured temperature rise is likely not to be a problem for any of the apex equipment (i.e. the nutator mechanism).
As noted by AlWootten
, an action item for Science from the Systems Requirements Review (SRR) was to fill out the "calibration examples". These "examples" should be used as "atomic" descriptions of each type of calibration, upon which we can build descriptions ("use cases", if you will) of how each type of calibration will be executed.
We now have drafts of most of these example documents in-hand. A Calibration Examples Wiki
page has been set-up for this group writing task. A final version of a document which describes the step-by-step process by which amplitude calibration is done, by RobertLucas
, has been posted to give an example of what I think we are looking for.
The following "volunteers" have been assigned to write these documents:
All should read the drafts and post comments to the CalExamples wiki. Those drafts which have not yet been posted should be made available to the group by April 1, 2006 so that everyone will have time to read them by our our next telecon.
It was suggested by JohnRicher that we hold focussed reviews of these calibration example documents. JeffMangum believes that this is a good idea. How about we discuss the Amplitude and Phase example documents at our next telecon. This will require everyone to have read these documents before the meeting and for the authors of both to be present.
- Amplitude and Flux Calibration (RobertLucas, JeffMangum)
- Phase Calibration (MarkHoldaway)
- Bandpass Calibration (RobertLucas)
- Polarization Calibration (StevenMyers)
- Pointing Calibration (JeffMangum)
- Antenna Location Calibration (MarkHoldaway)
- Antenna and Electronic Delay Calibration (RobertLucas)
- Optics Calibration (BaltasarVilaVilaro)
- Total Power Calibration (MarkHoldaway)
- Primary Beam Calibration (MarkHoldaway)
- ACA Calibration Issues (EdFomalont, MarkHoldaway)
- Solar Observation Calibration (MarkHoldaway)
Amplitude Calibration Subsystem Development Reports
- Berkeley Absolute Flux Calibration System (JimGibson)
- Formulating plan for calibration system waveguide measurements.
- Writing ApJ paper on absolute calibration system.
- Will distribute "system implementation" plan for ALMA absolute amplitude calibration system development to group.
- Semi-Transparent Vane (STV) Calibration System (ThomasWilson)
- Need only to get final report from Jesus Martin-Pintado. This is still pending.
- Multi/Dual-Load (M/DL) Calibration System (Matt Carter)
Amplitude Calibration Requirement Description
Please read and comment on a draft "amplitude calibration requirement description" document on the The ALMA Amplitude Calibration Requirement
Weather (Ancilliary) Measurement Devices
has started working on actual hardware specification for weather instrument systems. No new progress on this. Note that current target date for purchase of ancilliary calibration instrumentation is 2007/12/01.
On a related issue, the demise of the Site Characterization work has implications for installation of weather monitoring information at the OSF. What instrumentation can and/or should be moved from the site to the OSF for the antenna characterization and integration work to be done at the OSF? Several people made comments on this issue:
- Wind Bird: Lars pointed out that the Davis wind monitor is the only wind measuring device that can be read remotely (i.e. dumped to a database for remote access). This instrument can be moved from the site to the OSF with little difficulty.
- Hygrometer/Temperature/Pressure: Simplest option is to use the Buck CR4 currently installed in the ALMA/US site characterization container. Lars and Angel Otarola have pointed out that this device likely needs to be recalibrated. Estimated cost $500-$3500.
- Temperature Sounder: Even though the temperature sounder will be needed for monitoring of the atmospheric temperature profile on the site, we will need to purchase it as soon as possible in order to get experience with this measurement system.
Calibration Needs for Cross-Correlation of the ACA and the Main Array (EdFomalont)
The most relevant question within this topic for the calibration group is whether there is any significant gain for the ACA and ALMA arrays to be cross-correlated. The first-cut answer is "not enough in view of the large effort needed for this capability". See CalAca
is iterating on this issue further with NAOJ scientists.
Please see the
ACA Calibration Plan
which was discussed at the ACA System Review. Please post comments/discussion on this issue to the CalAca wiki. In order to close this issue by our next telecon, please comment by March 1, 2006.
- 09 Mar 2006: Suggests the following points for discussion:
The basic question is the following: are there any reasons not to correlate ALMA and the ACA? None were presented. Therefore, from a science perspective, all antennas on the site (ACA 7m, ALMA 12m, ACA 12m) must be available for combined and simultaneous observations.
The next thing for EdFomalont is to work on an "examples" document to describe how the ACA/ALMA calibration will be done.
- Some concensus and recommendations about the coordinated versus simultaneous use of the ACA and ALMA. Are we leaning toward simultaneous use when both arrays are needed for the science project? Does this mean coordination of ALMA/ACA scheduling?
- Are there any differences between the needed ALMA and the ACA calibrations? Going down Table 4 in the ACA Calibration Specifications and Requirements, I don't see any.
- Some calibrations, where strong sources can be used, can be done by a small number of telescopes with or without ALMA/ACA connection, and using the individual correlators. Some of these are:
- Initial pointing model for the sky
- Subreflector, feed settings
- Antenna motion
- Antenna location (although ALMA and ACA must tie in sometimes)
- Geometric, Electronic Delay (average bandpass included)
- Sideband ratio
- Lowish frequency Atmosphere delay
- Calibrations that require high sensitivity and must use as many array elements as possible are:
- Reference pointing
- Atmosphere delay at highish frequencies
- Primary beam properties in all Stokes parameters
- Polarization calibration (maybe)
- Accurate bandpass properties
- I think that some of the total-power ACA calibrations may be different, but I have no expertise about this.
- I envision a more united effort for ALMA plus ACA for many aspects of the combined arrays. The most important driver is better quality science for many reasons besides increased SNR. However, there are other considerations, some of which are political.
ASAC is concerned about ALMA's ability to achieve 1% repeatability for "relative" (in-band) amplitude calibration. We need to address a repeatability specification.
See discussion in 20060209 Calibration Group Minutes. BaltasarVilaVilaro is working on a memo which does many of these calculations.
WVR Tests on the SMA
See Richard's report and followup reports. Currently doing more thorough analysis of the existing test data. In particular, they are looking into correlation between cloud cover and poor phase stability as measured with the WVRs. JohnRicher mentioned that there will be a science meeting on WVR systems in Germany on 2007/10/9-10.
Date of Next Phone Meeting
The next ALMA Calibration Group telecon will be 2006, June 8th 15:00 UT
- 11 May 2006