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A few thoughts on scanning strategy

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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A few thoughts on scanning strategy

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  1. A few thoughts on scanning strategy F. R. Bouchet, M. Bucher, F. X. Désert, N. Ponthieu, M. Piat

  2. 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

  3. 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

  4. Example: WMAP • Short term redundancy on all angular scales • Good angular redundancy on most of the sky

  5. 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

  6. Exploring the parameter space Trajectory of one pixel on the sky

  7. 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

  8. 1 day, detector at r/3 (=2.5deg) Nhits cos2

  9. 10 days, detector at r/3 (=2.5deg) Nhits cos2

  10. 30 days, detector at r/3 (=2.5deg) Nhits cos2

  11. 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.

  12. 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

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