N A W G ======= NRAO Algorithms Working Group Meeting - MINUTES Date: 2005-7-13 (Wednesday) Time: 1300 MDT = 1500 EDT Video Hub: CV-conf (others call in) Rooms: SOC317/CV311/GB241/TUCN505 =============================================================================== Send corrections or additions for inclusion to smyers 1. Organizational issues o solicitation of topics for future meetings (Steve) It was suggested that someone (Harvey?) present the status of RFI issues. For example, it was noted that by 2009 the move to HDTV will free up some TV bands (these seem to be channels 52 - 69 from 600-800 MHz). It was also suggested that there was some RFI work done by some of the Green Bank gang (references?). 2. Project-related (ALMA, EVLA, GBT, VLBA, &c.) issues o Algorithms Workshop - it was suggested by Bill Cotton that an "Algorithms Workshop" be convened sometime in the fall. This would mostly be NRAO people but we could (should?) include interested experts from other groups (ATA, CARMA, LWA, MWA, US-SKA, etc.). This seems to me to be an excellent idea! o Collaborations with Jodrell Bank (and/or NFRA) - Bill had discussions with Phil Diamond and Walter Jaffe about collaborating on algorithm development problems (in particular wide-band imaging). I had similar discussions back in the spring at the JB RadioNet meeting. I think this is worth pursuing. 3. ***Short Topics*** - Presentations and Discussion Items ******************************************************************* o URSI Jan 2006 - Mel Wright and I are co-organizing sessions at the Boulder URSI meeting on Calibration and Imaging Algorithms. Interested parties from NRAO (also UNM and NMT) should consider attending - the dates are Wed Jan 4 - Sat Jan 7 (the week before the AAS) with our session tentatively scheduled for Fri Jan 6. There are also sessions on Focal Plane Technology and Spectrum Management. Suggestions for speakers and topics also welcome. See: http://astro.uchicago.edu/ursi-comm-J/ ******************************************************************* 4. ***Main Event*** - Presentations and Discussion Items ******************************************************************* o Sanjay Bhatnagar, Urvashi Rao-Venkata, and possibly Bill Cotton Summary of "SKA Wide-Field Imaging Workshop" held in Dwingeloo, NL 22-24 June 2005, and discussion of common development areas with NRAO (e.g. EVLA). Talks are online at the meeting website: http://www.skatelescope.org/pages/news/Wrksp20220605.htm Some particular talks discussed: Ger de Bruyn - WSRT LFFE low frequency imaging Gerry Harp - ATA wide-field imaging (and holography) Tim Cornwell - a cautionary tale of peeling Tom Osterloo - Peeling for Dummies Discussion: - "Peeling" definitely seems to be the buzzword these days, but it is unclear just how far this gets you particularly with requirements for high dynamic range imaging and in the presence of many sources in the field which all contribute to errors. Still, it seems to be the easiest thing to try and will definitely be needed to handle the bright sources in the (far) sidelobes and for RFI. I was curious if some coherent calibration model could be made from all the self-cal solutions on the peeled sources (to say interpolate for solutions on weaker sources using some spatial interpolation kernel); as I understand it the solutions are effectively thrown away after each source is "peeled" (though perhaps the cal solutions remain in tables). - It was noted that array designs that are optimized for imaging may have problems in calibration (e.g. some antennas orphaned at the ends of spiral arms with no short baselines). Not clear what the right trade-off is, maybe something like ring arrays? Also not clear if redundancy is good or not (the WSRT images look good though, maybe they are gaining alot from redundancy, maybe not). - Not much talk about RFI excision (and ultra-wide-field effect!). I guess we aren't the only ones reluctant to open that can of worms! ******************************************************************* 5. Future events (please sign up!) o George Moellenbrock - an update on frequency-dependent polcal (main) o Walter Brisken - a proposed self-cal modification (short) 6. Relevant reading: o Paper & Memos: - Beyond the isoplanatic patch in the VLA Low-frequency Sky Survey (W.D. Cotton et al.) Abstract: http://link.aip.org/link/%3FPSISDG/5489/180/1 - Solving for the Antenna Based Pointing Errors (Bhatnagar, Cornwell & Golap) http://www.aoc.nrao.edu/evla/geninfo/memoseries/evlamemo84.pdf - EVLA and SKA Computing Costs for Wide Field Imaging (Cornwell) http://www.aoc.nrao.edu/evla/geninfo/memoseries/evlamemo77.pdf - W Projection: A New Algorithm for Non-Coplanar Baselines (Cornwell, Golap, Bhatnagar) http://www.aoc.nrao.edu/evla/geninfo/memoseries/evlamemo67.pdf - Effects of Atmospheric Emission Fluctuations and Gain Fluctuations on Continuum Total Power Observations with ALMA (Holdaway) http://www.mma.nrao.edu/memos/html-memos/abstracts/abs490.html http://www.mma.nrao.edu/memos/html-memos/alma490/memo490.pdf o Post-processing requirements: - ALMA Offline Data Processing Requirements http://www.alma.nrao.edu/development/computing/docs/joint/0018/ALMAoffline-sw-18.pdf - EVLA Offline Data Processing Requirements http://www.aoc.nrao.edu/~smyers/evla/evla_offline.pdf o GBT: - GBT Software Review Agenda & Presentations http://wiki.gb.nrao.edu/bin/view/Software/ReviewAgenda2004 - GBT Standard Observing Modes http://wiki.gb.nrao.edu/bin/view/Observing/StandardObservingModes 7. Upcoming meetings and deadlines: o 2005 Jun 8-10 OSA Signal Recovery and Synthesis (Charlotte) o 2005 Jun 22-24 SKA Wide-field Imaging Workshop (Dwingeloo) o 2005 Jul 13 NAWG meeting ******************************************************************* o NAWG Website: http://www.aoc.nrao.edu/~smyers/nawg/ *******************************************************************