1N. Ponthieu BPOL @Rome, March 30th, 2007

A few thoughts on scanning strategy

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

2N. Ponthieu BPOL @Rome, March 30th, 2007

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

3N. Ponthieu BPOL @Rome, March 30th, 2007

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

4N. Ponthieu BPOL @Rome, March 30th, 2007

Example: WMAP

• Short term redundancy on all angular scales

• Good angular redundancy on most of the sky

5N. Ponthieu BPOL @Rome, March 30th, 2007

Examples: parameterization

• 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

WMAP

Planck

EPIC

6N. Ponthieu BPOL @Rome, March 30th, 2007

Exploring the parameter space

Trajectory of one pixel on the sky

7N. Ponthieu BPOL @Rome, March 30th, 2007

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

8N. Ponthieu BPOL @Rome, March 30th, 2007

1 day, detector at r/3 (=2.5deg)

Nhits cos2

€

cos2α2

+ sin2α2

9N. Ponthieu BPOL @Rome, March 30th, 2007

10 days, detector at r/3 (=2.5deg)

Nhits cos2

€

cos2α2

+ sin2α2

10N. Ponthieu BPOL @Rome, March 30th, 2007

30 days, detector at r/3 (=2.5deg)

Nhits cos2

€

cos2α2

+ sin2α2

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

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.

12N. Ponthieu BPOL @Rome, March 30th, 2007

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