The ADCanalog to digital converter non linearity correction is affecting the modulated signal of the bolometers before 40 of these fast samples are averaged and transmitted to the ground. The TOI data delivered in the HFI(Planck) High Frequency Instrument products are made of these average values. The raw signal of a bolometer for one modulation period is transmitted only at sparce intervals. This results in a complicated process to remove the systematic effects associated with ADCanalog to digital converter non linearity on the modulated signal taking into account the 40 Hz parasitics associated with the 4K cooler drive electronics.
The principles of the correction are detailed in the Planck-2015-A07. The correction cannot be done using only the TOI values but requires ancillary data from ground based tests and additional tests done during the LFI(Planck) Low Frequency Instrument extension of the mission when the dilution cooler did not operate anymore. For this reason, there is no reason to detail more than what was described in the paper as the users cannot expect to improve this part of the processing.
- Planck 2015 results. VII. High Frequency Instrument data processing: Time-ordered information and beam processing, Planck Collaboration, 2016, A&A, 594, A7.