LBNL-2016: Time-Ordered Data Processing

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Time-Ordered Data Processing Birds-of-a-Feather Session: Wednesday, March 9, 9 AM

Attending: Julian Borrill, Tom Crawford, Ted Kisner, Kris Gorski, Graca Rocha, Clem Pryke, Nick Harrington, Jesse Treu, Kyle Story, Nathan Whitehorn, Olivier Perdereau, Reijo Keskitalo


Discussion of TOD scanning simulations

  • Scanning with full 4-pi beam: do we really get the 4-pi beam at high fidelity?
    • at some level, not the data folks' problem.
  • Are we really going to simulate full TODs, including data that we will eventually cut in the real TOD?
    • yes, at least to test automated data cuts.
    • who is going to take on the task of creating this model?
    • we pretty much know how to do it now, unless the fundamental detector and/or readout architecture changes.
  • Do we need to simulate TES & electronics response?
    • Not a high priority. Assume detectors/electronics with funky response will not pass CD.
  • RFI pickup?
    • Impossible to implement in sims without model of pickup.
  • Time-dependent focal plane / optics distortion?
    • Real-world examples to go on from ACT & PB
  • We need scan strategy to be defined to do sims.
    • Is anyone considering using anything but azimuth scans as fast and wide as you can go?

Digression into computing plan

  • Are we really going to use grid computing (rather than parallel processing on large clusters)?
    • Certainly not for anything for which we have to send around real TOD. (I.e., just for sims.)
  • What about data management / delivery from sites?
    • Pole bandwidth barely accommodates SPT-3G and will be unlikely to increase enough to handle S4. Similar issues exist in Atacama.

Return to TOD sims

  • Will there be half-wave plates on S4?
    • Can't rule it out. How do you make a model of non-ideality for a HWP?
  • Are we aiming to have a perfect set of TOD sims by summer or 10 years from now?
    • There will be a profile of what we can simulate. Could in theory have some level of TOD sims by summer.
  • What about atmosphere?
    • Moving slab prototypes exist.
  • Loudly stated that TOD sims will not be used in the 3-month timescale forecasting.
    • OK, but is there something we can do on the next timescale (~6 months)
    • At least agree on common inputs & data formats.
      • That's coming up soon.

Time to Pixel Domain

  • Are preprocessing steps included in instrument?
    • In a perfect world, yes.
  • Are we discussing mapmaking procedures yet?
    • They should all be implementable. Though ML-mapping will be hard from Pole.

Implementation Issues

  • Everything will be driven by data volume.
    • First step is to avoid I/O as much as possible.
  • How to accommodate two analysis modes (interactive development on small number of timestreams vs. full-TOD MCs)?
    • Does a python-based codebase disfavor HPC?
    • Not fundamentally, but it would be great to be able to swap in a C/C++ module for the corresponding python module seamlessly.
    • Everyone agrees that Healpix is the right pixel format.
    • Use currently implemented cut-sky Healpix format in FITS?
      • That is not using any of the advantages of FITS and incurring many disadvantages.
      • Sounds like we have decided to use hdf5 and take on the job of writing a healpy interface.
  • Scalable software used at LBNL
    • python-based implementation of LFI control & mapmaking (PyTOAST calling libmadam)
  • Will we be able to run different Stage-3 experiments' data through each others' pipelines?
    • [raucous laughter ensues]
    • Perhaps require that all S3 experiments' data run on their own pipeline and a common pipeline.
    • Some consensus achieved that S4 pipeline will be high-level python with some C/C++ under the hood.

Word of the day: Exciting

Literary allusions

All perfect data sets are identical; each imperfect data set is imperfect in its own way. (Anna Karenina)

First, we kill all the I/O. (Henry VI)

Gotcha scorecard

TIme Deliverer Receiver
9:59 Ted Nathan
11:20 Ted, on behalf of Nathan Ted