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?
  • Can we produce cleaned, calibrated, timelines as inputs for both map-making and noise/systematics residuals estimation?
  • Help needed on pre-processing & mission characterization subsection.

Component Separation:

File:Comp sep 2 slides.pdf

  • multi-site 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, 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 requirements timeline (see forecasting, v&v)?


  • Awareness that forecasting for r versus higher-ell TT/TE/EE/kk parameters v kSZ/tSZ parameters is done differently
  • How many different experiments set-ups should we consider? (bands, sensitivity, sky area)
    • How to define "units of effort" to judge tradeoffs?
  • What noise model should we use? (can we draw on Stage 2/3 expts) What systematics assumptions?
  • What foreground model(s) should be used at low-ell for r and at high-ell for lensing etc (and can we share with other experiments)?
    • Can we agree on role of map-level "mocks" to validate forecasts?
  • What shall we assume about delensing residuals for r?
  • Can we conclude whether we need <40 and >270 GHz data?
  • What is the forecasting requirements timeline?

Validation & Verification

  • Can we produce standardized data sets for V&V? Can these overlap with forecasting?

Implementation Issues:

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

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