# Difference between revisions of "Power spectra"

We call intra-frequency checks those performed between detectors (or sets of detectors) in the same frequency bands, which thus respond similarly to the sky emission. Interfrequency-checks on the other hand correspond to checks between detector in different frequency bands, imposing further reliance on a sky model to perform the test.

## Intra-frequency checks

These compare the power spectra between various detector sets operating within the same frequency channel. They see the same sky, and should therefore give consistent results, up to the noise level, and up to color corrections due to their somewhat different spectral band passes. These corrections are rather small if one restricts the comparison to specific portions of the sky, for instance dominated by extra-Galactic components, like it is done for extracting the CMB power spectrum in the likelihood analysis where \$f_{sky} \sim 0.4\$.

Consistency checks

The pictures shows in grey the prior deduced from the beam parameters uncertainty analysis. At 217 GHz, the distance between PSB and SWB suggests an accounted for effect (fortunately small enough for the likelihood analysis). The relative calibration appear to be at the 0.1% level.

This shows that whatever systematic effect might remain, it has to be common to all detectors within a frequency band to a very high level of accuracy.

(Planck) High Frequency Instrument

Cosmic Microwave background