Glossary

• 4-K lines: EMI/EMC influence of the 4-K cooler mechanical motion on the bolometer readout electronics.
• bandpass: same as the spectral response.
• calibration:
  • HFI - For a single detector, the absolute calibration is the gain factor between the measured signal (watts absorbed by the detector) and the sky signal (in astrophysical units); it can vary with time. For a set of detectors, the relative calibration is the difference in the calibration between detector pairs. The latter can be measured very accurately from the observations of the same source by different detectors, and is only slightly affected by the differences in the detector spectral responses, which are similar; the former requires observations of sources with well modelled spectral energy distributions or well known spectra, and requires that the detector's spectral bandpass is also well known.
  • LFI - absolute calibration refers to the 0th order calibration for each channel, one single number, while the relative calibration refers to the component of the calibration that varies from pointing period to pointing period.
• detector set: for HFI, a detector set (also known as "detset" or "quad") is a combinaison of two pairs of polarization sensitive bolometer pairs at the proper orientations. The list of detsets is given here.
• DMC: Data Management Component, the databases used at the HFI and LFI DPCs.
• effective beam: the effective beam at the map level is the overall angular response to the sky in a map pixel, which results from the combined effect of the instrumental response, the scanning strategy, and the data processing.
• far sidelobe: the response to the sky of a detector more than 5° from the beam centroid.
• half-ring difference: difference between the map built using the first half of each pointing period (typically 20 minutes of contiguous data) and the one built with the second half. This difference effectively removes the sky signal and most of the correlated noise, leaving only the noise components that have time scales below about 20 min.
• HEALPix: (Hierarchical Equal Area isoLatitude Pixelation of a sphere ) pixelation scheme used to produce Planck sky maps (and HFI HPR).
• HPR: for the HFI, HEALPix Rings are introduced to avoid any additional binning of the data. We choose the sky pixelization as a basis for this ring making. HPR are therefore partial sky maps produced via a projection onto the sky of each single pointing period separately.
• IMO: the HFI Instrument MOdel is a central repository containing the models (or a link to them) and sets of fixed parameters used in these models describing for example how photons are gathered and transformed into data. The IMO is oriented toward the data reduction and data processing. The IMO is also used to monitor the instrument health and represents at any time the official knowledge of the instrument response. It is intended to represent the best current knowledge agreed on by the project and applicable to the data processing. The IMO does not represent the knowledge of the instrument; it is knowledge of the instrument's response, (e.g., how photons are gathered and transformed into data). It is a simplified fraction of this knowledge directly useful for reducing the data. The IMO is restricted to the sole parameters used in the DPC. It does not contain timelines or maps, although it can provide links to calibration timelines (e.g., gain evolution) and calibration maps (e.g., beam maps). Models do not need to be unique (there is not a single model for a single process). Depending on the purpose for which they are used, they can be more or less sophisticated (e.g., bolometer models, beam representations, simplifications for the first assessment of pointing parameters, …); the IMO does not choose between them, but contains the parameters for each of them at the same time. See also HFI RIMO.
• jump: sudden change of the baseline level inside a ring.
• main beam: response to the sky within a given (instrument-dependent) angle of the centroid of the response. The angles are as follows:
  • HFI - 23' for all frequencies;
  • LFI -
    • 30GHz, 1.89°;
    • 44GHz, 1.32°;
    • 70GHz, 0.86°.
• near sidelobe: response to the sky between the outer limit of the main beam and 5° of the main centroid of the response:
  • HFI - 23'-5°;
  • LFI -
    • 30GHz, 1.89°-5°;
    • 44GHz, 1.32°-5°;
    • 70GHz, 0.86°-5°.
• OD: Operation Day, whose definition is geometric visibility driven, since it runs from the start of a DTCP (satellite Acquisition Of Signal) to the start of the next DTCP. Given the different ground stations and different duration that the spacecraft takes for them, the OD duration varies, but it is basically once a day.
• optical beam: the response to the sky due to optics alone.
• PBR: for the HFI, Phase Binned Rings provide a compressed and higher signal-to-noise ratio rendition of the original Time Order Data.
• polarization leakage: in general, systematic effects mix the I, Q, U signals. Given the amplitudes of the sky signals, leakage from temperature to polarization can be dramatic for polarization analysis.
• RIMO: the RIMO, or Reduced Instrument MOdel is a FITS file containing selected instrument characteristics that are needed by users who work with the released data products.
• ring: at the HFI DPC level the ring is the time interval between two First Thurster Firings, as defined in AHF description document. It thus starts with a satellite slew (and thus an unstable pointing period) and continues with a satellite dwell (and thus stable pointing period).
• scanning beam:
  • HFI - the scanning beam is defined as the beam measured from the response to a point source of the full optical and electronic system, after filtering;
  • LFI - the actual beam that couples the optics of the instrument with the scanning movement of the satellite (beam smearing), which can be measured from planet observations.
• SOVT : System Operation and Validation Test.
• spectral response (or bandpass): the steady state response of a detector system (i.e., detector and its electronics + horn + filter) as a function of frequency. It does not consider the temporal response and associated transfer function.
• survey: sky surveys (aka Scan #) are defined in terms of the direction of the satellite's spin axis. Survey periods are given here.
• TOD :
  • HFI - Time-Ordered Data;
  • LFI - Time-Ordered Data, refering specifically to calibrated data.
• TOI:
  • HFI - Time-Ordered Information;
  • LFI - Time-Ordered Information, refering to uncalibrated data.
• warm units: JFET, bellows, PAU, and REU.