[mmaimcal] Imaging and Calibration Tasks during Construction

[Al Wootten]

Division Heads are supposed to think about dividing up the construction 
project--what do we want and what do we really not want.  Here is my
proposal for calibration and imaging.

I found the philosophy which Peter and others espoused compelling:
ALMA/US should develop tasks that have technical advantages
for other ALMA/US telescopes; they should pursue any task that we feel strongly 
that ALMA/US does better.  Note, I would not be so parochial as to
use the term NRAO here; the MDC is part of this project also and should
continue to be so.

These are in WBS number.  The most important of all items here is
WVR.  This is the most critical issue facing ALMA, and there has been very
little ALMA/EU work on it.  I think it absolutely necessary for the success
of ALMA that ALMA/US/MDC continue this work, as explained below.

+--------------------------------------------------------+
WBS 10.05
Science requirements is an ongoing joint venture.
+--------------------------------------------------------+
WBS 10.10
Site operations will become more under the aegis of Division 2, site
development, and I presume will be subsumed there in the construction phase,
though we will still need to monitor and analyze data on site 'weather'.
+--------------------------------------------------------+
WBS 10.15
Configurations should be decided by construction.  There may still be issues 
with the larger configuration but this is a joint area, IMHO.
+--------------------------------------------------------+
WBS 10.20
Calibration is under active investigation by ALMA/US.  Currently, BIMA has
developed a prototype calibration system.  Mangum and Plambeck are writing
a memo which will propose a system targeted at achieving the 1% accuracy
sought by the ASAC.  Guilloteau is reportedly considering a calibration
system which will involve the available 183 GHz radiometer (WVR).  I propose 
that ALMA/US continue investigation of load measurement calibration techniques,
and that ALMA/EU continue investigation of how to incorporate the WVR
into the calibration system.  This split follows the philisophy mentioned in
the first paragraph.
+--------------------------------------------------------+
WBS 10.25.05
There will continue to be imaging issues.  I forsee ongoing simulation
with AIPS++ as the array gets better and better defined.  This should be an
area of ALMA/US leadership, as it has been so far, with considerable
European involvement.
+--------------------------------------------------------+
WBS 10.25.10
Water vapor radiometry.  This is the most crucial issue facing operation of
ALMA, in my opinion.  Without it, ALMA will not work to specifications
on the longer baselines
or at the higher frequencies.  So far, tests show promise but they are a
very long way from achieving the level of correction needed for ALMA.
OVRO, the VLA and probably BIMA are currently operating 22 GHz systems, with
various levels of application.  ALMA/EU is constructing a Mark II 183 GHz
radiometer, which may go on the prototypes or not (I haven't had an answer).
However, in my opinion the development of the algorithms for application of
the phase correction, and its implementation in day to day use is the most
important necessity for progress.  There has been none of this work in Europe,
except for continuum work at PdBI and a few somewhat successful handcrafted
demonstrations with the now closed CSO-JCMT interferometer.  We don't know
when the PdBI will open, and they will be hard pressed to introduce new
facilities when they do open, as other items (the new telescope) are top
priority.  On the other hand, OVRO has demonstrated a working system, now
has cooled receivers which will provide routine corrections on all baselines.
BIMA has several scanning monitors of Alan Rogers design and will introduce
phase correction in the future.  The VLA is probably furthest behind at the
moment, but will eventually apply phase corrections on a scale similar to that
we need for ALMA.  The philosophy mentioned above clearly calls for ALMA/US
to continue development of 22 GHz phase correction systems at OVRO, BIMA
and the VLA--this is a system with great benefit for the ALMA/US
telescopes, it is a task which ALMA/US has developed to its highest state
in the world today, and it is essential for successful operation of ALMA.

Were ALMA/EU to adopt a similar philosophy, it would clearly call for them
to continue development of the 183 GHz system.  This is an area of leadership
for them, and it is an area with direct application to the SMA/JCMT system.
However, application will be several years away, both for the SMA/JCMT
and for PdBI.  

It seems to me that a necessary and useful split here would be hardware to
Europe and algorithms/application to the US.

Al
+--------------------------------------------------------+
| Alwyn  Wootten   (http://www.cv.nrao.edu/~awootten/)	 |
| Project Scientist, Atacama Large Millimeter Array/US   |
| Astronomer, National Radio Astronomy Observatory       |        
| 520 Edgemont Road, Charlottesville, VA 22903-2475, USA |
| (804)-296-0329 voice             Help us build The ALMA|        
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