The LFI DPC

Overview

LFI DPC processing is organized into several different levels, numbered 1 to 4 and S. In brief, Level 1 has the purpose of analysing 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 DPC database. Level 2 uses the output of Level 1, 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 and LFI DPCs to derive astrophysical results such as source catalogues, CMB maps, and foreground maps. Level S is the common simulation pipeline used to validate the results as well as to test 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 (PLA).

Level 1: From packets to TOI

Level 1 takes input from the Mission Operation Centre's (MOC's) Data Distribution System (DDS), decompresses the raw data, and outputs time-ordered information for Level 2. The inputs to Level 1 are the telemetry (T/M) and auxiliary data as they are released by the MOC. Level 1 uses T/M data for performing a routine analysis of the S/C and P/L 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 T/M, to monitor the operation of the observation plan and to verify the behaviour of the instrument. Additional tasks of Level 1 relate to its role for instrument control and as the DPC interface with the MOC. Level-1 processing is described in detail in the pre-processing section.

Level 2: From TOI to maps

The DPC 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 4-K reference load. These 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 by 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, 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 components

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 CMB, 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, a description of global or statistical properties, etc.). Data from both HFI and LFI are analysed jointly to reach the final results. Level-3 processing is described in detail in the Power Spectra and HFI/LFI joint data processing sections.

Level S: Common HFI/LFI 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, PSM), 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 section.

LFI DPC infrastructure

The LFI DPC provides centralized hardware and software infrastructure to a large number of geographically distributed institutions participating in the Planck mission. Briefly, the data are interfaced to a database, where only meta-information is stored. This allows for very high flexibility to enable modification of the products that are to be delivered.

Published paper

A description of the pipeline applied to the Early Planck results can be found in Planck-2013-V, while instrument performance is reported in Planck-2013-III.

The description of the pipeline applied to the 2015 Planck release can be found in Planck-2015-A03, systematic effects are detailed in Planck-2015-A04, beams and window functions in Planck-2015-A05, and calibration in Planck-2015-A06. Finally the LFI mapmaking procedure is described in Planck-2015-A07.

Final description of the pipeline applied to the 2018 Planck release can be found in ADD Planck 2018 results. II. Low freq instr data process.