The LFI DPC

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Overview

LFI(Planck) Low Frequency Instrument DPCData Processing Center processing is organized into several different levels, numbered 1 to 4 and S. In brief, Level 1 has the purpose of analyzing the data received from the satellite on a daily basis, transforming the telemetry packets into timelines containing engineering values and feeding the results to the DPCData Processing Center database. Level 2 uses the output of Level1, transforming raw TOI into calibrated timelines with all the known systematic effects removed; those timelines are then used in the mapmaking process to create all desired map combinations. Level 3 uses the Level 2 output of both HFI(Planck) High Frequency Instrument and LFI(Planck) Low Frequency Instrument DPCs to derive astrophysical results like source catalogues, CMBCosmic Microwave background maps, foreground maps, etc. Level S is the common simulation pipeline used to validate the results and any algorithm before its introduction into the official pipeline. Finally Level 4 merely acts to reformat, document and deliver the products to the final archive (PLAPlanck Legacy Archive).


From packets to TOI

Level 1 takes input from the MOC[ESA's] Mission Operation Center [Darmstadt, Germany]’s Data Distribution System (DDSMOC's Data Distribution System), decompresses the raw data, and outputs Time Ordered Information for Level 2. The inputs to Level 1 are the telemetry (TM) and auxiliary data as they are released by the MOC[ESA's] Mission Operation Center [Darmstadt, Germany] (Mission Operation Centre). Level 1 uses TM data for performing a routine analysis of the S/CSpacecraft and P/LPayload with the aim of monitoring the overall health of the payload and detecting possible anomalies. Level 1 also includes a quick-look analysis of the science TM to monitor the operation of the observation plan and to verify the behavior of the instrument. Additional tasks of Level 1 relate to its role of instrument control and as the DPCData Processing Center interface with the MOC[ESA's] Mission Operation Center [Darmstadt, Germany]. Level-1 processing is described in detail in the Pre-processing section.


Level 2: From TOI to Maps


The DPCData Processing Center Level 2 has many tasks. The first one is the creation of differenced data. Level 1 stores measurements made from both the sky and the 4K reference load. These two have to be properly combined to produce differenced data, greatly reducing the impact of 1/f noise. This is done via the computation of the so-called gain modulation factor “R” which is derived taking the ratio of the mean signals from both sky and load. After differenced data are produced, the next step is the removal of known systematic effects followed by photometric calibration[LFI meaning]: absolute calibration refers to the 0th order calibration for each channel, 1 single number, while the relative calibration refers to the component of the calibration that varies pointing period by pointing period., where ‘calibrated’ means essentially that the TOD are in physical units instead of engineering units. The next major task is the production of frequency maps calibrated and free from systematic effects (which is a complex task and involves several sub-pipelines). Level 2 processing is described in detail in the TOI processing section.


Level 3: From Maps to Component

The aim of Level 3 is to transform the frequency maps produced by both instruments into preliminary maps of the underlying astrophysical components, including the CMBCosmic Microwave background, by means of pipeline processing, as well as to provide other data sets including catalogues of astrophysical sources (compact source lists, extended source maps and catalogues, description of global or statistical properties, etc …). Data from both HFI(Planck) High Frequency Instrument and LFI(Planck) Low Frequency Instrument are analyzed jointly to reach the final expected results. Level-3 processing is described in detail in the Power Spectra and HFI/LFI joint data processing section.


Level S : A common HFI(Planck) High Frequency Instrument/LFI(Planck) Low Frequency Instrument simulation software


Level S is the so-called "Simulation Level" software suite common to both consortia, which, given a sky model (generated by the Planck sky model, PSMPlanck Sky Model), detector pointing and beams, generates a model of the sky and hence of the power reaching each detector. It can also provide a simplified description of quantities such as the noise. It is further described in the HFI/LFI joint data processing.


LFI(Planck) Low Frequency Instrument DPCData Processing Center Infrastructures

The LFI(Planck) Low Frequency Instrument DPCData Processing Center provides a centralized hardware and software infrastructure to a large number of geographically distributed institutions participating to the Planck mission. Briefly, the data are interfaced to a database where only meta-information is stored. This allows very high flexibility to eventually modify the product to be delivered


Published Paper

The description of the pipeline applied to the Early Planck results can be found in Planck-2013-V[1], and instrument performances are reported in Planck-2013-III[2].

The description of the pipeline applied to the 2015 Planck release can be found in Planck-2015-A03[3], systematic effects are detailed in Planck-2015-A04[4], beams and window functions in Planck-2015-A05[5] and calibration in Planck-2015-A06[6]. Finally the LFI(Planck) Low Frequency Instrument map making is described in Planck-2015-A07[7].

References

  1. Planck 2013 results. V. LFI Calibration, Planck Collaboration, 2014, A&A, 571, A5
  2. Planck 2013 results. III. Low Frequency Instrument systematic uncertainties, Planck Collaboration, 2014, A&A, 571, A3
  3. Planck 2015 results. II. LFI processing, Planck Collaboration, 2016, A&A, 594, A2.
  4. Planck 2015 results. III. LFI systematics, Planck Collaboration, 2016, A&A, 594, A3.
  5. Planck 2015 results. IV. LFI beams and window functions, Planck Collaboration, 2016, A&A, 594, A4.
  6. Planck 2015 results. V. LFI calibration, Planck Collaboration, 2016, A&A, 594, A5.
  7. Planck 2015 results. VI. LFI mapmaking, Planck Collaboration, 2016, A&A, 594, A6.