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titlebf Report of the ALMA Scientific Advisory Committee:
September 2002 Meeting
titlebf October 15, 2002
sectionCalibration labelcalibration
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S. Guilloteau presented the current status of calibration work
in the project. The ASAC was pleased to see that a Calibration Group
had recently formed, with B. Butler of NRAO leading this. The ASAC
look forward to working with this group in restating and refining the
calibration requirements which affect the scientific capabilities of
ALMA.
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Although it appreciates that this group has only just started its
work, the ASAC remains concerned that a clear calibration plan for
ALMA is still lacking. The ASAC recommends that a work plan which
addresses all the calibration issues for ALMA, with a clear timeline
indicating design reviews and decision points, be established over the
next six months. In particular defining the minimum hardware required
for calibration seems to be urgent, given the budget pressures in the
project. For example, whether there is a need for one or more FTS
systems, 60 GHz sounders, polarization widgets, and a coherent photonic
calibration signal should be rapidly established. A presentation
and/or a paper from the Calibration Group on its plans at the next
ASAC meeting would be welcomed and would help the ASAC advise on
scientific implications of the calibration schemes under
consideration.
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Regarding amplitude calibration, the ASAC was pleased to see the
semi-transparent vane system had made progress, with a preliminary
ALMA design available, and that there were plans for construction of a
prototype on a millimeter dish. Although already tested as a prototype
at BIMA, the status of the dual load system is less clear, and the
ASAC recommends that a decision on this system be made rapidly by the
Calibration Group.
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The ASAC also recommends that a framework for deciding on the future
of the coherent photonic calibration system be established as part of
the calibration group's planning.
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Finally, the ASAC reaffirms the unique scientific value of accurate
polarization measurements from ALMA, and urges the calibration group
to include polarization calibration as a vital part of its planning;
polarization calibration should be included in the overall plan
presented to the ASAC at its next meeting.
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The ASAC makes the following recommendations concerning the Calibration:
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beginitemize
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The ASAC recommends that a plan which addresses all the calibration
issues for ALMA, with a clear timeline indicating design reviews and
decision points, be established over the next six months.
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item
The ASAC recommends that the minimum hardware required for calibration
be established over the next 12 months, or as soon as is practicable.
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item
The ASAC recommends that a decision on the dual-load calibration
system be made rapidly by the Calibration Group.
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item
The ASAC recommends that a framework for deciding on the future of the
coherent photonic calibration system be established as part of the
calibration group's planning.
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item
The ASAC recommends that the calibration group include polarization
calibration as part of its planning, and present a report to the ASAC
at its next meeting on progress in defining a definite plan for
polarization calibration.
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enditemize
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