2007-09-13 ALMA Calibration Group Telecon Agenda and Minutes


ALMA Calibration Group Telecon
  • Date: September 13, 2007 (Thursday)
  • Time: 14:00 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.


Attendees

  1. JeffMangum
  2. Richard Hills
  3. JohnRicher
  4. AlWootten


Calibration Examples Status

RobertLucas has produced a final version of the delay calibration example, which has been posted to CalExamples wiki. BaltasarVilaVilaro has produced another version of the optics calibration example. Please read and comment. See CalExamples wiki for further information. Note that Calibration Sequence information is now included in each CalExamples document.


Amplitude Calibration Subsystem Development Reports

Multi/Dual-Load (M/DL) Calibration System (Ferdinand Patt)

  • Ferdinand Patt sent final version of ALMA Calibration Device: Prototype Calibration Load Test Report (FEND-40.06.04.00-005-A-REP); Murk and Duric (2007) (or on EDM ).
  • As noted during our last telecon, several issues from load report need resolution. Basic problem is that it is not possible to optimize the backscatter, total scatter, and thermal performance of a load system with a single type of absorber. Since the amplitude calibration sequence will involve comparisons of spectral measurements of the loads, standing waves are a problem. See CalAmp wiki page for further details.
  • As noted during our last telecon, the need to provide a hot load which meets the temperature stability requirement from 30 to 900 GHz is the main limitation. According to Patt and Murk, if the hot calibration load were not needed for Bands 1 and 2, then it would be easier to meet the overall hot load temperature stability requirement. On 2007/09/07 JeffMangum made some calculations of the accuracy of the single- and dual-load calibration systems at Bands 1 (40 GHz) and 2 (80 GHz). Following the same formalism described in Load Calibration at Millimeter and Submillimeter Wavelengths: Mangum; October 18, 2002; ALMA Memo 434 the situation is directly analogous to the calculation done at 230 GHz. Assuming 50th-percentile tau(40)=0.02+-0.002 and tau(80)=0.03+-0.003 the single-load (traditional) chopper uncertainty is ~1.2% at both frequencies under "best" conditions (as laid out in Memo 434) assuming double sideband operation. The total uncertainty is significantly dominated by the uncertainty in the sideband gain ratio and the uncertainty in the rear scattering and spillover plus radiative efficiencies (etal). Note that this analysis assumes that the frontends do not suffer affects due to saturation.

It was pointed out by Richard that in fact Bands 1 and 2 will use HEMPT's and not SIS mixers, so they will be intrinsically SSB. One can then eliminate this element of the calibration error. Recalculating with sigma(Ri)=0 yields a single-load chopper uncertainty of 1% which is completely dominated by the uncertainty in etal.


Berkeley Absolute Flux Calibration System (Jack Welch)

  • No report.


Ancilliary Measurement Devices

Weather Station (P,T,RH,Ws,Wd) Instrumentation

In December 2006 JeffMangum submitted weather station instrumentation (RH, P, T, and wind) RFQ documentation to NRAO procurement system. After having reviewed information received from bidders and consulted with Calibration Group (see CalAncillary for discussion), on 2007/03/21 JeffMangum submitted purchase information to RobertLaing for procurement. Leonardo Testi received first set of weather measurement devices at ESO in late September. Will assemble unit at ESO for testing.

ICD submitted for AOS site locations discussed during August meeting. A few kinks under discussion with computing and site include power distribution (440V needs transformer) and fiber lighting (only done when antenna occupies station).


Solar Observations and Calibration

MarkHoldaway has written a draft document on Calibration of Solar Observations. We discussed this document at our last telecon. Few revisions are needed. JeffMangum will pick-up the last draft produced by Mark and update.

It was noted by Richard that Mark's scheme for doing solar amplitude calibration might be a bit pessimistic. If one could alternately observe with half of the antennas with solar filter in and the other half with load in, the loss in observing efficiency could be significantly reduced. Richard will bounce this off of Mark.


Date of Next Phone Meeting

The next ALMA Calibration Group telecon will be 2007, October 11th 14:00 UT.

-- JeffMangum - 13 Sep 2007

This topic: ALMA > WebHome > AlmaSci > AlmaCal > CalAgendaMinutes > CalAgendaMinutes20070913
Topic revision: 2007-10-09, JeffMangum
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