LBNL-2016: Simulations & Data Analysis

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Simulations & Data Analysis Parallel Session: Monday, March 7, 10:45 AM - 11:45 AM

Session Organizers: Tom Crawford & Julian Borrill

Chapter Section Coordinators:

  • Time-Ordered Data Processing: Julian Borrill
  • Component Separation: Josquin Errard
  • Statistics & Parameters: Tom Crawford & Cora Dvorkin
  • Sky Modeling: Nick Battaglia & Jacques Delabrouille
  • Data simulation: Julian Borrill
  • Forecasting: Jo Dunkley & John Kovac
  • Validation & Verification: Julian Borrill
  • Implementation Issues: Julian Borrill

(with many thanks to all of the other people who contributed to this draft)

Charge For This Session

What we are charged with achieving in this session is, according to the workshop wiki page ( "The goal for each of these sessions it to determine missing content and outstanding questions for their chapter. It is particularly important to address what they need from the larger community. During the Plenary session in the afternoon, the drafters will present their findings with emphasis on the issues for which community input is sought."

With that in mind, we ask that each section coordinator be prepared to discuss (briefly! we only have 10 minutes per section) the 1 or 2 questions that define the scope of your section, in particular questions that are still open after the writing of this draft of the chapter (and questions that require input from the larger meeting, so that we can bring those up in the plenary).

Please gather those questions---and any supporting figures or other material (but no big slide presentations, please)---in the sections below.

Rapid-fire Sessions (1 per chapter section)

Time-Ordered Data Processing:

  • Multi-site/multi-telescope pre-processing challenges - should we be targeting a common data model after pre-processing?
  • Help needed on pre-processing & mission characterization subsection.

Component Separation:

File:Comp sep 2 slides.pdf

  • multi-sites data - various resolutions leading to a “degraded” resolution for the final CMB map; common data pre-processing is required.
  • pixel vs harmonic domain - all methods should work independently of this choice, but computational needs should be checked.
  • Q/U vs E/B component separation - implications should be checked on simulations
  • atmospheric residuals - although unpolarized, atmosphere scales with frequency in a similar way as a grey body.

Statistics & Parameters:

File:Dvorkin Statistics and Parameters CMBS4 March2016.pdf

Outstanding questions / What do we need from the community:

  • For Science Book writing:
  1. How to coordinate with the discussions of parameter-constraint-related issues in other sections (like de-lensing)?
  • For general planning (in no particular order)
  1. Covariance approximation sufficiency (Are there more covariance issues we haven't thought about? What about combining with optical?)
  2. At what stage do we combine data sets? (This may be treated in other sections too.)
  3. Do we have a plan for E/B separation? Will this be done the same way in every data set?
  4. What is the path toward more realistic de-lensing estimates?

Sky Modeling:

Galactic foregrounds

  • Can we agree on nominal model sims and set of extensions that include more complex foreground behaviour?
  • Example of new code created for this purpose:
  • Is there a planned release of PSM soon?

Secondaries and extragalactic foregrounds

  • The key challenges for the extragalactic sky models of CMB-S4 are to provide fast and self-consistent simulations of CMB secondary anisotropies and extragalactic sources.
  • Modular approach with many groups contributing.



  • What format? HEALPIX?
  • Reasonably well in hand exactly, but when do we need this by? Deadlines are always good...

Data Simulation

  • Prioritization of systematic effects to be introduced
  • (How) can we achieve consistency of their representations across domains (time/pixel/multipole)?


  • What is the forecasting requirements timeline?
  • What are the common assumptions for forecasting?
  • Can we develop common sky/mission models for forecasting?
    • Can we share sky model inputs with other (especially space) experiments - Planck, LiteBIRD, (Lite)COrE+, ...
    • Can we borrow mission model inputs from other (especially stage-3) experiments?

Validation & Verification

  • Can we design forecasting datasets that also serve V&V?

Implementation Issues:

  • (Evolving) computing resources & requirements
  • Common data interfaces, objects & formats
    • Sky & mission models
    • Maps!

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