Date: 20 April 2000.
Time: 11:00am EDT.
Phone: (804)296-7082 (CV SoundStation Conference phone)
Past minutes, etc on ALMA Configuration Group Page
Present were B. Butler, J. Conway, M. Holdaway, K. Morita, F. Schwab, A. Wootten, and M. Yun.
Minutes
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New topographical mask. A new topographical mask with a more limited N-S shadowing consideration is now available at B. Butler's web site. It is in the same format as before. For the moment, the coordinates for the second piperline to the north is not available, and it is assumed to be running parallel to the Jama road for now.
Simulation Image Library. Eight people have voted on the selection of the candidate images, including 3 members of the ASAC (not including M. Yun). The five images selected for the imaging study are: model protoplanetary disk, Mars, Cygnus A, M51 H-alpha, and 850 mircon SCUBA dust cloud image. The fits images will be made available shortly on one of the configuarion working group web page.
Updates on strawperson configurations. M. Yun is finalizing the strawperson donut configurations using the new topo mask and 10% N-S elongation. The resulting pad positions will be posted on the working group page shortly. J. Conway will do the same for the log spiral array as well.
J. Conway had asked F. Boone to try a further optimization of the log spiral configuration using his Gaussian beam optimization routine, but the result was not much different from a random perturbation case.
F. Schwab comments that too much emphasis is given to producing a Gaussian uv-distribution because there is no need to bunch up the visibilities in the central core where the visibility is already well determined with high S/N. Rewighting by software may be a better way to go. J. Conway objects that this reweighting adds noise nevertheless. The real impact of this reweighting needs to be investigated before either of these theoretical points can be substantiated. Also, as B. Butler comments, this brings up the need for more sophisticated software for apodization and image construction.
Adding noise in simulations. Further comments were exchanged over the issue of not including any noise in the simulations. It is widely agreed that different errors (such as pointing or thermal) can easily swamp any imaging defects resulting from different uv-coverages being tested. On the other hand, the intent of not including any noise at this stage is to avoid including too many free parameters that will make the evaluation impossible.
J. Conway will put some effort into examining the impact of phase noise on imaging. Residual phase noise with a fast switching should be constant beyond some baseline lengths, but there may be some excess, baseline dependent phase noise if a radiometric correction is used. E. Keto pointed out previously that a zoom spiral array requires longer baselines for the same resolution as a donut or a ring array. Self-calibration may offer a solution in some cases, but this may be an exception than a norm.
A. Wootten reminds the group that the project book chapter is due this week, and M. Yun will make final touches to the draft version.