2006-02-09 ALMA Calibration Group Telecon Agenda and Minutes

ALMA Calibration Group Telecon
  • Date: February 09, 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

Table of Contents:

Complete List of Action Items

Action Items from Last Telecon

Assigned To Due Date Description State Notify  

Agenda and Minutes

NOTE: Discussion from the telecon is shown in italic.


  1. EdFomalont
  2. JimGibson
  3. Richard Hills
  4. RobertLucas
  5. JeffMangum
  6. AnthonyRemijan
  7. Jack Welch
  8. AlWootten

Calibration Examples

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 a few 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 and JeffMangum, 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:

  1. Amplitude and Flux Calibration (RobertLucas, JeffMangum)
  2. Phase Calibration (MarkHoldaway)
  3. Bandpass Calibration (RobertLucas)
  4. Polarization Calibration (StevenMyers)
  5. Pointing Calibration (JeffMangum)
  6. Antenna Location Calibration (MarkHoldaway)
  7. Antenna and Electronic Delay Calibration (RobertLucas)
  8. Optics Calibration (BaltasarVilaVilaro)
  9. Total Power Calibration (MarkHoldaway)
  10. Primary Beam Calibration (MarkHoldaway)
  11. ACA Calibration Issues (EdFomalont, MarkHoldaway)

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 March 1, 2006 so that everyone will have time to read them by our our next telecon.

Amplitude Calibration Subsystem Development Reports

  • Berkeley Absolute Flux Calibration System (JimGibson)
    • Have plan for test at 3mm on CARMA.
    • Need ambient temperature structure to get atmospheric opacity to make this technique work properly.
  • Semi-Transparent Vane (STV) Calibration System (ThomasWilson)
    • Need only to get final report from Jesus Martin-Pintado. Reminder has been sent.
  • Multi/Dual-Load (M/DL) Calibration System (Matt Carter)
    • No new news to report.

Weather (Ancilliary) Measurement Devices

JeffMangum has started working on actual hardware specification for weather instrument systems.

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 for EdFomalont summary. EdFomalont 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.

ASAC Comments on Calibration in ALMA Science Requirements

See the October 2005 ASAC Report, section 4 (their Charge 2). The ASAC would like clarification on a few issues regarding amplitude calibration stability and polarization and primary beam calibration requirements. This item is closed.

ASAC Comments on "Relative" Amplitude Calibration (2006/01)

ASAC is concerned about ALMA's ability to achieve 1% repeatability for "relative" (in-band) amplitude calibration. We need to address a repeatability specification. Questions:

  • Is 1% repeatability achievable?
    • Unlikely. For relative calibration both in-band and cross-band repeatability will be driven by differences in:
      • Atmospheric opacity
      • Beam patterns
      • Black body load emission characteristics
      • Amplitude decorrelation (goes as nu^2)
  • To what degree does this depend on the atmospheric conditions?
    • This is probably the largest contribution to the repeatability.
  • Can we achieve 1% repeatability (including the ACA) only under the top 5% atmospheric conditions at 900 GHz?
    • Perhaps. Should look at and/or extend calculations presented in ALMA Memo 434 to get a handle on this.
Assigned to Due date Description State Notify  
JeffMangum 2006-07-01 Do in-band and cross-band analysis of relative amplitude calibration repeatability (similar analysis to that presented in ALMA Memo 434). (go to action) closed JeffMangum edit
* Frequency dependence?
    • Probably. At least amplitude decorrelation.

WVR Tests on the SMA

_Cambridge WVR currently being tested on two SMA antennas. Radiometers used are the two prototypes (correlation and dual-dicke) systems. Have taken data side-by-side and see excellent correlation. SMA receiver problems have slowed progress. Should have results soon. Richard has provided a WVR test progress report.

ALMA Science Requirements

The ALMA Science Requirements is nearing the end of the approval process. Please read and comment. This item is closed.

Date of Next Phone Meeting

The next ALMA Calibration Group telecon will be 2006, March 9th 15:00 UT.

-- JeffMangum - 09 Feb 2006
Topic attachments
I Attachment Action Size Date Who Comment
Phase_calibration_steps.txttxt Phase_calibration_steps.txt manage 6 K 2006-02-08 - 09:09 EdFomalont Comments on Phase_calibration steps
Topic revision: r7 - 2009-04-01, JeffMangum
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