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A few thoughts on scanning strategy. F. R. Bouchet, M. Bucher, F. X. Désert, N. Ponthieu , M. Piat. Polarized map making in principle. Minimum. Solution :. Covariance matrix of I, Q, U. Redundancy together with angular homogeneity impact on the S/N + IQU decorrelation.

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slide1

A few thoughts on scanning strategy

F. R. Bouchet, M. Bucher, F. X. Désert, N. Ponthieu, M. Piat

slide2

Polarized map making in principle

Minimum

Solution :

Covariance matrix of I, Q, U

Redundancy together with angular homogeneity impact on the S/N + IQU decorrelation

An intuitive estimator of the quality of the pointing is

slide3

Polarization systematics mitigation

  • The main systematic effects are not spin-2 quantities, so they average out if the angular coverage is homogeneous
  • Especially true for the most ‘’serious’’ ones like differential gain
  • Can gain 1 order of magnitude in rejection between two scanning strategies

Scanning strategy is the first tool for systematic mitigation

Hu et al, 2004

Ponthieu & Hivon, 2007 in prep

slide4

Example: WMAP

  • Short term redundancy on all angular scales
  • Good angular redundancy on most of the sky
slide5

Examples: parameterization

WMAP

Planck

  • Planck
    •  = 85 deg, Tspin = 60 sec
    • a = 10 deg, Tprec = 6 months
  • EPIC/JPL
    •  = 45 deg, Tspin = 63 sec
    • a = 50 deg, Tprec = 3.2 h

EPIC

slide6

Exploring the parameter space

Trajectory of one pixel on the sky

slide7

Exploring the parameter space

  • Parameters:
    • 3 angles
    • 3 rotation speeds
  • Goal:
    • Short term redundancy on all angular scales
    • Large fraction of the sky covered in a few days
    • Good angular coverage
    • Jacknife possibilities
  • some constraints
    • The scan speed of the line of sight must be compatible with the beam, the detector time constant
    • The sampling rate must be compatible with the telemetry (if no onboard aggressive data compression)
    • Cope with thermal effects, solar pannels orientation, SCAO etc…

Example of set of parameters:

T = 43200 sec

T = 2400 sec

T = 20 sec

 = 45

 = 45

slide11

Figures of merit

  • Redundancy and homogeneity
  • Want some more deeply integrated regions to really dig into systematics ? Calibration ?
  • How deep do we want to integrate vs how much sky do we want to cover in the same amount of time ?
  • … etc…

At this stage of the study, we did not have to quantify exactly the benefit from a particular set of parameters. But we did find one that is feasible and meets the constraints we set.

slide12

Conclusion

  • Scanning strategy is essential to sensitivity
  • It is the first tool to mitigate systematic effects
  • Is is a powerful tool
  • It is a strong driver of the mission architecture
  • non homogeneous sky coverage compromises E/B separation
  • It will be a strong driver of the data analysis, compression…? Cf. Radek’s talk