NGVLA CSV Working group: 2019 Feb 19 Telecon

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  • Date: Tues 19 Feb 2019, 20 UT = 15 ET = 13 MT
  • Location: CV-ER230, SO-280
    • Audio Hub: 434-817-6283
  • Participants:
    • CV: Todd, John, Jeff
    • SO: Joan, Rafael, Vivek, Barry, Rob
    • Audio: Bryan
    • unavailable: Eric, Chris


  1. Account code to charge on your timecards for this work: 251200000
  2. Discuss comments on the first draft of the CSV Concept
    • A) Interaction with AIV, including initial unification (discussed by AIV group)
      • TRH: Do we need to formalize this in more detail, perhaps in a new section? (Currently, interaction is mentioned via examples in section 3 and via milestones in 8.1.)
      • TRH: Should we split list of initial milestones in CSV Concept into a combined AIV+CSV list (to go into both documents?), followed by a CSV-specific list?
    • B) Barry's comments
      • "the document makes a lot of assumptions about the design, which are still a bit unclear at this time. Better if the document were made more design neutral."
        • TRH - which assumptions? (WVRs? Walsh functions?)
      • "I would be happier if this document were less specific, and included mostly general concepts, like the idea that there need to be several teams, working in some degree in parallel, to commission different capabilities, and how those capabilities change as array construction progresses."
        • Current list of CSV subgroups: long baseline, short baseline, autocorrelation, RFI
        • Other possibilities? ephemeris, phased array, polarization, astrometry
    • C) Jeff's comments
      • Need to add section on "how we commission the data processing / pipeline." Issues to discuss?
      • Operators are a personnel requirement (sect. 6.3): does CSV have their own or do we use Operations staff?
  3. Devise an "Order of Capabilities to be commissioned" (new chapter)
    • BGC - some depend on others working well, and, in reality not everything will be available at the end of construction.
    • BGC - Where does long baseline stuff come in the early science plan?
    • Discuss implications of the Reference Observing Program of 5 Key Science Goals, circulated by Joan on Friday
Correlator setup Spatial mode
  Single Pointing Pointed Mosaic OTF Mosaic Phased array Number of cases Number of KSG
Continuum KSG 1, KSG 5.2 (LBA)   KSG 5.1, 5.3, 5.4 KSG 4, KSG 5.5 7 3
1 or a few lines KSG 3.2, 3.4 KSG 3.1, 3.3, 3.5     5 1
Many lines KSG 2       1 1
Number of cases 5 3 3 2    
Number of KSGs 4 1 1 2    
Legend: KSG1=Solar System Analogs, KSG2=Astrochemistry, KSG3=Galaxies, KSG4=Pulsars, KSG5=Black Holes

Next telecon

  1. March 19: Make CSV Concept document consistent with AIV Concept document
  2. late April: begin planning the next document

Notes (DONE means action completed)

  • On the AIV-CSV bifurcation point:
    • JK proposes it to be when independent subarray operation is delivered
    • RH: this should be a CSV milestone, then
    • JK: it may be one of the more difficult deliverables for the correlator
    • TH: is there a proposed date for subarrays in C&S concept? No...
    • RS: don't worry about dates yet
    • BB: Need list of hoops, time estimates and their dependencies
    • JK: Need to hold a project-wide negotiation session on the order of deliverables (like subarrays)
    • DONE ACTION 1: TRH to add subarray capability delivery to the milestone list
  • On the use of VLA as testbed -- it is not mentioned as a possibility in this document
    • BB: WVR will be tested that way
    • general feeling: differences in rx/electronics packages will be too large for this to be cost effective
  • On the extent of initial single dish activities
    • BGC: pointing (and other stuff) is easier with interferometry
    • BB/TH/JK: there will be a period where all we have is one antenna; also would be more comfortable using antennas with some demonstration of reasonable performance before attempting interferometry
    • TH: we also must deliver single dish imaging capability to science at some point
    • BGC: No money should be spent on special hardware detectors for single dish
    • agreed: we should force existing components to work, including autocorrelation
    • DONE ACTION 2: TRH to leave this milestone in place, but move detailed sub-points to the CSV Plan document (as with other milestone details)
  • Holography ruminations (part 2)
    • it is the furthest distant antennas of the Main array which are most challenging, not the LBA as they have 3 close stations each
    • BGC: VLBA holography was diffcult because you had to record everything instead of playing around in real-time.
    • BGC: Asterisk scan pattern (repeatedly passing through central pointing) can help counteract phase instability
    • TRH: ALMA implemented this mode for their celestial holography
    • BB/VD?: phase stable conditions rare, bandwidth too low for good sensitivity off-axis
    • TRH: current plan envisions satellite holography (with small fixed reference antenna) as an option
    • someone: Can Out-of-focus (OOF) holography be used? (which does not require a reference antenna or extra receiver)
    • TRH: OOF is used frequently for high freq observing at GBT, can give up to 6th order Zernike polynomial surface measurement; might not be enough depending on ngVLA surface design (number of panels, adjusters)
    • RS: There are 160 adjustment points in NRC design. Correction after meeting: strike the 160 in favor of "many"
    • DONE ACTION 3: RS to send TRH a link for the value of adjusters. See URSI presentation by D. Chalmers where it does not quote a number of adjusters yet (still in design), but looks like at least a few dozen
    • DONE ACTION 4: TRH to emphasize that surface method validation to be used depends heavily on the antenna design, add brief mention of OOF
  • How should shared AIV+CSV milestones (up through subarrays) be presented?
    • TRH: should they be separated from the rest of CSV milestones, and placed in both documents?
    • general agreement (I think)
    • DONE ACTION 5: TRH to re-organize and send this idea to Chris
  • On making the document less specific to the design, what examples besides changing "Walsh functions" to "spurious signal suppression"
    • BGC: not clear if switched noise power is useful
    • VD/BB: yes, they provide good diagnostics (even if observers don't use them)
    • BB: could use lower duty cycle than VLA
    • RS: gain corrections are part of the plan
    • BB: Calibration doc will mention switched power
    • DONE ACTION 6: TRH to change validate "Walsh functions" to validate "spurious signal suppression" (and similarly for any other overly-specific items)
    • DONE ACTION 7: TRH to review if/how switched power is mentioned in the milestone details (that get moved to the CSV Plan)
  • On the topic of Operators for CSV
    • RS: strong preference for financial reason for Operations Group to provide the operator staff that we need
    • DONE ACTION 8: TRH to put this operator idea into Assumptions section and Required Personnel section
  • On the "Commissioning the data center" idea raised by Jeff
    • because data processing in the Operations Concept is described (in section 6.1) as "automatically-generated and quality assured SRDPs", i.e. non-interactive
    • VD: we want local capability to process data for AIV
    • JK: AIV+CSV will need access to small portions of the data; should also strive to replicate issues under investigation with smallest number of antennas
    • BGC: cluster executions has its own problems
    • BB/JH/others: is this a CSV responsibility? may be asking too much
    • JK: CSV needs to show that data can be acquired and processed through the same path as PI data
    • TRH: Need to remember that there is a staged delivery of capabilities here, since ES starts in 2028 while CSV is not complete until 2034. Agree we should meet JK's goal by 2034, but reality in 2028
    • DONE ACTION 9: TRH to add appropriate text to the Concept
  • Brief discussion on Order of Capabilities to be commissioned
    • JK: the word Capabilities may be overloaded here. "science modes" or something else may be better
    • TRH: In the table, I split up the Key Science Goals from the ROP into 2-axes: correlator setup and spatial extent (single pointing/ mosaic / phase array)
    • TRH: Single pointing continuum is most common, though many items in ngVLA Science book are not represented
    • JW: Would be good to mention that pointed mosaics require good primary beam models
    • TRH: it is a good idea to list which of the commissioned quantities (like primary beam) are extra important for different Science Modes. Something for the Plan document.
    • ACTION 10 on all: Send me ideas you have on this topic, since we have run out of time
  • Small Baseline Array
    • where does SBA fit into KSGs?: ROP says nothing about it nor total power
    • VD: when do SBA antennas arrive? RS: in the midst of the main antennas...
    • General feeling is that CSV focus would be on main array, then SBA, then total power
  • Other comments:
    • VD: Move C8 (test calibration plan) earlier in the list, perhaps to C4
    • JW: June VLA meeting will expand the scope of Key Science Goals
    • TRH: SV targets need to be chosen by CSV in consultation with project scientist and community. Joan expressed interest in coordinating this effort.

-- ToddHunter - 2019-02-15
Topic revision: r8 - 2019-03-19, ToddHunter
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