[1101.2720] Observational Scan Induced Artificial CMB Aniso
Posted: January 21 2011
Here's another contribution from Liu and Li on scan-induced artifacts in CMB maps, continuing on the discourse from here: http://cosmocoffee.info/viewtopic.php?t=1537
Here they derive a general way to express many possible observational effects (timing offsets as in their previous work, errors in determining the sidelobe response of the detector, etc) as an effective error in the antenna line of sight direction which is constant in the spacecraft coordinate frame. They also come up with a way to clean errors of this form from maps, and demonstrate that they can recover the true input quadrupole from a simulated map even with a large artificial quadrupole on top of it.
What I find especially interesting here is that they actually make some predictions for Planck, so this will help resolve the issue of what's actually going on. Although they are careful to say that they can't fully calculate what's expected from Planck before the Planck data is released: "Note that the exact templates of scan-induced anisotropies can be calculated when the real Planck data release is available. ... Our calculations are based on the simulated Planck scanning scheme with assumed initial conditions of scan geometry. The real pattern of the scan-induced Planck quadrupole could hence be some kind of rotation or sign reversion to the ones shown here." Regardless, should be very interesting to revisit when the first Planck cosmological results appear!
Here they derive a general way to express many possible observational effects (timing offsets as in their previous work, errors in determining the sidelobe response of the detector, etc) as an effective error in the antenna line of sight direction which is constant in the spacecraft coordinate frame. They also come up with a way to clean errors of this form from maps, and demonstrate that they can recover the true input quadrupole from a simulated map even with a large artificial quadrupole on top of it.
What I find especially interesting here is that they actually make some predictions for Planck, so this will help resolve the issue of what's actually going on. Although they are careful to say that they can't fully calculate what's expected from Planck before the Planck data is released: "Note that the exact templates of scan-induced anisotropies can be calculated when the real Planck data release is available. ... Our calculations are based on the simulated Planck scanning scheme with assumed initial conditions of scan geometry. The real pattern of the scan-induced Planck quadrupole could hence be some kind of rotation or sign reversion to the ones shown here." Regardless, should be very interesting to revisit when the first Planck cosmological results appear!