Minutes for meeting Mon, 18 October 1999 at 4pm EDT.
Date: 18 October 1999
Time: 4:00 pm EDT (2:00 pm Socorro, 1:00 pm Tucson)
Phone: (804)296-7082 (CV SoundStation Premier Conference phone).
Past minutes, etc on MMA Imaging and Calibration Division Page
Minutes
--------
Science Working Group
The Science Working group is responsible for defining the "Science Requirements" and
maintaining adequate contacts with the other groups to reflect these requirements in the design.
For completeness, we summarize here the main design goals derived from high level scientific
requirements:
High sensitivity
- optimal receiver design for sensitivity
- dual polarisation
- excellent site
- high performance antennas
- High precision LO system
- Wide IF
High angular resolution
- 10 km baseline
- Atmospheric phase correction system
High fidelity imaging
- Reconfigurable array -- Transportable antennas
- Precision pointing (< 0.6")
- Precision amplitude calibration
- Good instantaneous UV coverage
- High precision LO system
- Atmospheric phase correction system
- Fast switching for phase correction
Wide Field of view
- Mosaicing capability
- Total power capability
- Compact array configuration
- Precision amplitude and phase calibration
- Fast correlator dump times -- High data rates
Wide Frequency coverage
- large dewar
- Coverage of all atmospheric windows up to 900 GHz
- High precision tunable LO system
- Fast tuning capability
Polarisation Capability
- Measure all Stokes parameters
- Cross polarisation in correlator
- Appropriate calibration techniques
All purpose instrument
- VLBI phased array mode
- Pulsar "gating" mode
- "Easy to use" concept from Proposal submission to Data analysis
- Complete data archive
- Flexible scheduling for "Target of Opportunity" cases
Within its main goal, the Science Working group will have the following objectives
A.1 Define the Science Goals
A.2 Perform end-to-end simulation on representative images
A.3 Define the "Data Product" of ALMA
A.4 Define the data pipeline processing
A.5 Define the calibration strategy
A.6 Define the observation strategy
A.7 Define priority orders among the Science Goals, to allow preparation
of a progressive implementation plan.
Points A.1 to A.6 are general issues. Within these points, there are some critical items to be
assessed because they may influence the global design or specification of the array. Such items
are reflected in the WBS.
Point A.7 requires a cost-benefit analysis which goes beyond simple specifications and requires
feed-back from the design teams and funding profile. In this area, there is in general to critical
decision, but rather a timing problem to match development timescales and funding timescales
to the astronomical needs. However a few key parameters influence the global design of the
array, and have also been reflected in the WBS. The personnel plan have not been agreed yet,
so that names of institute or persons are only tentative. However, previous meetings show that
there is sufficient expertise to cover all the fields mentionned here. Manpower may limit the
extent to which some items are studied in Phase I. Emphasize will be put on items which
influence the design of the array (such as phase calibration strategies, lowest frequency, total
power mode, and of course configuration layout).
By essence, the Science Working group has to provide specifications to most areas of the ALMA
project, and to maintain close contact with most of them. Tight coupling has to be preserved with
the Software group, specially concerning the archiving and data analysis, and also with the
receiver and system group for all the calibration items. Close interaction with the ALMA SAC is
also within the group mandate, and this has been reflected on the European side by assigning
persons for formal liaison with the other groups.
The available manpower includes :
US side : A.Wootten, S.Radford, M.Yun, B.Butler, J.Schroeder.
European side : S.Guilloteau, J.Richer, F.Viallefond, R.Lucas, A.Dutrey,
R.Neri, J.Conway, A.Webster, P.Schilke, L.Testi, P.Cox, R.Hills, R.Guesten.
Additional support is possible to some level for specialized or high priority tasks. In particular, support from the AIPS++ group has been agreed upon for some software issues, and a parallel effort will go on at IRAM for the simulation, based on development made at DEMIRM.
10 ,Science, ,
10.1, Scientific requirements, Responsible, MMA-WBS
10.1.1, Overview, ,A.Wootten S.Guilloteau,
10.1.2, 35 GHz system , P.Cox ,
10.1.2.1 Scientific rationale,,
10.1.2.2, Impact on receiver -- cost -- feasibility, ,
10.1.2.3, Impact on LO system -- cost -- design, ,
10.1.2.4, Comparison with existing or planned instruments, ,
10.1.3, Very long baselines , K.Menten,
10.1.3.1, Scientific rationale,
10.1.3.2 , Impact on receiver -- cost -- feasibility -- prospects, ,
10.1.3.3 , Impact on LO system -- cost -- design -- prospects, ,
10.1.3.4, Possible limitation on the Baseline x Frequency product , ,
10.1.4, Prioritization of the frequency bands , ,
10.1.4.1, Scientific rationale, ,
10.1.4.2, Required bandwidth for each band, ,
10.1.4.3, Impact on receiver -- cost -- feasibility -- prospects,,
10.1.4.4, Impact on LO system -- cost -- design -- prospects, ,
10.1.4.5, Possible limitation on the Baseline x Frequency product, ,
10.1.4.6, Comparison with existing or planned instruments, ,
10.1.5 ,Data flow and archiving specifications ,,
10.1.5.1, Define data rates (min., typical, max.), ,
10.1.5.2, Define archiving policy (raw data, calibrated data, images), ,
10.1.5.3, Define standard pipeline, ,
10.1.5.4, Define non-standard modes , ,
10.2, Site Characterisation and Monitoring , S.Radford,
10.2.1, Atmospheric Stability , , 11.1.2
10.2.2, Atmospheric Transparency,, 11.1.3
10.2.3, Physical structure of atmosphere , , 11.1.4
10.3, Array design and Operation, ,
10.3.1, Compact configuration design , US / Europe, 11.2.1
10.3.2, Discrete intermediate configurations, NRAO , 11.2.2
10.3.3, Continuous intermediate configurations , Conway / Webster,
10.3.4, Long baseline configurations , , 11.2.2
10.3.5, Operating model , NRAO / IRAM,
, Scheduling , ,
, Reconfigurations, ,
, Calibration cycles, ,
10.3.6, Quick-look specification, NRAO / IRAM,
10.3.7, Automated quality assessment methods, NRAO / IRAM,
10.4 ,Calibration , ,
10.4.1, Total power mode , Richer / Emerson ?,
10.4.1.1 ,Develop simulation tools, ,
10.4.1.2, Prepare test images, ,
10.4.1.3 ,Perform simulations to evaluate required performances and observing
strategies to recover the shortest spacings through total power observations, , 10.4.1.4, Evaluate Wobbling sub-reflector, ,
10.4.1.5, Evaluate alternate route: large single-dishes, ,
10.4.1.6, Evaluate alternate route: array of smaller antennas, ,
10.4.2, Amplitude calibration strategy, ,
10.4.2.1, Develop system temperature calibration techniques, ,
10.4.2.2 ,Develop calibration techniques applicable to wide band backends
(to handle frequency dependent Tsys and atmospheric opacity), ,
10.4.2.3 ,Develop bandpass calibration strategies, ,
10.4.2.4, Develop polarisation calibration strategies, ,
10.4.3, Phase calibration strategy, ,
10.4.3.1, Develop atmospheric modeling techniques for phase retrieval through atmospheric power fluctuations, ,
10.4.3.2, 22 GHz devices., OVRO/NRAO , 11.3.1
10.4.3.3, 183 GHz devices,. UK (Hills) ,
10.4.3.4, Select optimal device and method, ,11.3.2
10.4.3.5, Incorporate fast switching technique into
observing strategy and data rates requirements, ,
10.5, Imaging Studies , , 11.4
10.5.1, Mosaicing, All,
10.5.2, Multi-scale deconvolution methods , NRAO/Demirm,
10.5.3, Develop "easy to use" simulation tools (from simple cases to comprehensive studies), NRAO/IRAM/Demirm, --------
--------
--------
Definition and Formation of Joint ALMA Science Advisory Committee
--------
What science will be lost if we have three or fewer subarrays?
From the
MINUTES OF ALMA SYSTEMS DESIGN TELECONFERENCE, 1999-OCT-13 LRD 1999-Oct-14
a. Subarray support: The draft shows a master subarray to which any or all of the 64 antennas can be assigned, and some TBD number of secondary subarrays, each of which can have up to 8 antennas. The restriction limits the number of fiber power amplifiers (EDFAs) to 8+K for K secondary subarrays, and simplifies the network of optical power dividers and switches. Shillue pointed out the EDFAs have significant noise figure and this must be included in the noise budget; yet it was agreed that they are needed to get enough power for 64 antennas. Payne suggested a different approach, where we use a separate laser synthesizer for every antenna; only the master laser would be common. This eliminates all switching and produces no restrictions on subarray assignments. (We still need 8 EDFA's for the master laser signal.) There was considerable support for this idea, in spite of the greatly increased cost. D'Addario agreed to study it. [After the meeting it occurred to me that this plan sacrifices most common-mode phase error cancellation for antennas operating together. However, such is also the case for the photonic-direct option, so it will have to be faced if that approach becomes the baseline.]