A few thoughts on scanning strategy
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Transcript of A few thoughts on scanning strategy
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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
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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
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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
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4N. Ponthieu BPOL @Rome, March 30th, 2007
Example: WMAP
• Short term redundancy on all angular scales
• Good angular redundancy on most of the sky
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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
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6N. Ponthieu BPOL @Rome, March 30th, 2007
Exploring the parameter space
Trajectory of one pixel on the sky
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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
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8N. Ponthieu BPOL @Rome, March 30th, 2007
1 day, detector at r/3 (=2.5deg)
Nhits cos2
€
cos2α2
+ sin2α2
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9N. Ponthieu BPOL @Rome, March 30th, 2007
10 days, detector at r/3 (=2.5deg)
Nhits cos2
€
cos2α2
+ sin2α2
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10N. Ponthieu BPOL @Rome, March 30th, 2007
30 days, detector at r/3 (=2.5deg)
Nhits cos2
€
cos2α2
+ sin2α2
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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.
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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