[mmaimcal] ImCal meeting

[Al Wootten]

Folks,

I caught a cold somewhere in the torrid heat of this trip and I don't
feel up to talking for an hour today, so let's not have the meeting. 
However I have typed up my notes and have almost finished a draft of the
committee report.  For my notes from the calpdr meeting, please see
http://www.cv.nrao.edu/~awootten/calpdr.html
and send me any comments you may have.

As for the committee report, I have not passed this by the members but
the gist of the comments I have is as follows:

The Committee believes that although a start has been made, there is a
substantial amount of work remaining before we can be sure that ALMA may
be calibrated to the desired accuracy.  

1) Getting an end-to-end description of the calibration system (whether
this be stability requirements on the hardware or calibration
observations or calibration technique) needs to be done. Moreno and
Guilloteau's work on the times required to calibrate the instrument is
also obviously an important adjunct to this.  

2) It is attention to detail in much of this work that is required in
the long run, and its too easy for approaches which involve
sophisticated modelling to fail to note or solve the real problems.  It
is important to prototype as much as possible of the calibration system,
and preferably in an environment which is as similar to Atacama as
possible.

3) The lack of coherent direction in the present design and development
stage of ALMA clearly reflects on work in the calibration area.  A
coordinated calibration group is needed to direct and assess efforts. 
At the present meeting, representatives of the system, receiver and
science groups were in attendance; this seems a sensible core for this
group.

There are also a number of action items, for which Stephane's list looks
pretty complete to me and contains:
1) really test the semi-transparent vane. It is simpler, but may not
work at all if we can't find suitable material

2) Perform computations    of the expected standing wave pattern.
Bernard
Lazareff volunteered here, but we need to supply him with all the
antenna / subreflector / receiver parameters.

3) Work out in more detail the hybrid phase calibration system (Fast +
WVR). This seems to be considered as trivial, but there hasn't been any
quantitative simulations here.

4) Reconsider seriously the photonic calibration device. This has not
progressed as much as I was anticipating, and I am worried that it may
actually not work. The radiating element properties is a serious
concern.

5) Convince the receiver group to give us some hints on expected
performance level. We cannot continue in the current situation where
they claim "we must have specifications on which we agree" and do not
give us any number at all... I perfectly understand John Payne's point :
getting these numbers will require work, but we should work together to
define the tasks required to obtain them.

Those who attended, please send comments, especially if you were on the
committee.  I'm two days behind in writing this!

As for other matters, the ALMA-GSMT synergy meeting is next Monday so
I'm trying to prepare for that.

Clear skies,
Al