Minutes of 14 April 2003 Telecon of USSKA Consortium
Written 14 April 2003  by JMC

In attendance: T. Beasley, B. Cotton, D. Bock, C. Carilli, 
J. Cordes, G. Cortes, D. DeBoer,  B. Gaensler, P. Goldsmith, 
D. Jones, K. Kellerman, J. Lazio, B. Preston,  J. Tarter, Y. Terzian, J. Welch 


The main goal of this telecon was to consider the Compliance Matrix
produced by the ISAC as an assessment of all SKA concepts, the 
US LNSD concept in particular.

JMC summarized the goals and pointed to relevant sections to the
draft document circulated on 13 April 2003.

Some initial comments on the draft included:

	Tarter: (1) Section I (Summary of the changes to the concept
		should mention alternative dish designs.  
	
		(2) An item to be emphasized should be bringing back
                signals from all antennas to the processing center,
		which implies flexibility and enables some of the
 		science areas.

	Welch:  Pointed out that 12m antennas can work at 100 MHz as
		counterpoint to some of the current text that suggests
		an alternative is needed.

	Lazio:  Commented that though the 12m antennas might work at
		100 MHz, that dipoles might be a better alternative for
		low-frequency science.

	Cordes: Commented that the particular low-f science areas might require
		a different design than dishes  to do it right.

	Beasley:  A general outlook is that we optimize for L band and
		take what we can get at low and high-f.

We began discussing items in the compliance matrix and then 
Chris Carilli gave an overview of the process for updating the matrix
and the status of the 9 science areas with respect to any prioritization
and definition of Level 0 science:

	- Better to keep all science areas on equal footing so as to
	  be inclusive.
	- At some point we'll need to prioritize for the sake of
	  defining Level 0 science.

	  Comments by others: we can't forsee what will be important 
	  > 10 years from now so we shouldn't be rigid in defining 
	  too-narrow goals for the SKA.

	  But ... we need to sell the SKA so we need notable science
	  goals comprising a short list.

	- Over the last two years there has been a large shift in
	  interest to high-frequency capability.  This exemplifies
	  the fluidity of the important science areas, as do
	  recent WMAP results which (correct or not) point toward
	  yet lower frequencies for the EoR.

	- The process  will consist of:
		a. updating the compliance matrices in advance of Geraldton
		b. addressing Level 0 science and the overall science case
			at the November 2003 ISAC retreat in Leiden.
		c. work on the SKA Science Book

There was discussion about the particular area of Galactic Nonthermal
Radiation and Magnetic Field, with regard to getting short u-v spacings.
Gaensler discussed usage of a small subset of antennas with much
closer spacings than typical in the core array; also usage of 
auxiliary (or existing) larger single-dish antennas.  The latter are
problematic for continuum radiation.  Tarter asked 
how we would decide on the short-spacing/inner-array issue
(with what metrics, etc.).  Responses centered on the scale-invariant
aspect of the current configuration and that the core array thus
could be defined as those antennas that can be directly processed
by a correlator/beam-former without mediation in a station.   However,
another aspect is the actual u-v spacings and their implications for
low-surface brightness coverage. 

Cordes discussed the issues for blind surveying of fast transients
(and pulsars and ETI) which require a large number of simultaneous
beams in order to cover the field of view,  which scales as
the square of (maximum baseline)/(dish diameter).  Tarter advocated
optimisim based on Moore's law but Cordes expressed the need to
be specific about real solutions for particular kinds of observations.

We ended after an hour having discussed only about 1/3 of the items
in the compliance matrix.   JMC proposed to update the draft
with some of today's discussion, including a section on configuration
issues suggested by Preston.  There was sentiment that we should
cover all items in the compliance matrix briefly and then concentrate
on the big issues, especially those that are common to several
science areas.