1. N. Ponthieu BPOL @Rome, March 30th, 2007 1 A few thoughts on scanning strategy F. R. Bouchet, M. Bucher, F. X. Désert, N. Ponthieu, M. Piat

2. N. Ponthieu BPOL @Rome, March 30th, 2007 2 Polarized map making in principle Solution : Covariance matrix of I, Q, U Redundancy together with angular homogeneity impact on the S/N + IQU decorrelation Minimum An intuitive estimator of the quality of the pointing is

3. N. Ponthieu BPOL @Rome, March 30th, 2007 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 Hu et al, 2004 Ponthieu & Hivon, 2007 in prep Scanning strategy is the first tool for systematic mitigation

4. N. Ponthieu BPOL @Rome, March 30th, 2007 4 Example: WMAP Short term redundancy on all angular scales Good angular redundancy on most of the sky

5. N. Ponthieu BPOL @Rome, March 30th, 2007 5 Examples: parameterization Planck –  = 85 deg, T spin = 60 sec – a = 10 deg, T prec = 6 months EPIC/JPL –  = 45 deg, T spin = 63 sec – a = 50 deg, T prec = 3.2 h WMAP Planck EPIC

6. N. Ponthieu BPOL @Rome, March 30th, 2007 6 Exploring the parameter space Trajectory of one pixel on the sky

7. N. Ponthieu BPOL @Rome, March 30th, 2007 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:  = 45  = 45 T  = 43200 sec T  = 2400 sec T  = 20 sec

8. N. Ponthieu BPOL @Rome, March 30th, 2007 8 1 day, detector at r/3 (  =2.5deg) N hits cos2 

9. N. Ponthieu BPOL @Rome, March 30th, 2007 9 10 days, detector at r/3 (  =2.5deg) N hits cos2 

10. N. Ponthieu BPOL @Rome, March 30th, 2007 10 30 days, detector at r/3 (  =2.5deg) N hits cos2 

11. N. Ponthieu BPOL @Rome, March 30th, 2007 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. N. Ponthieu BPOL @Rome, March 30th, 2007 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