The LFI DPC

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Contents of this chapter

Overview

Pre-processing

Overview • Telemetry data • Pointing data • Orbit data • Time correlation data

TOI processing

Overview • Input TOI • General Pipeline Structure • Output TOIs and products • Examples of clean TOIs • Trends in the output processing variables • Flag description

Pointing&Beams

Detector Pointing • Scanning Beams • Effective Beams

Map-Making and photometric calibration

Introduction • Photometric calibration • Building of Maps • Noise properties • Zodi correction • Far Sidelobe Correction • CO Correction • Map validation

Spectral response

TBW

Internal overall validation

Expected systematics and tests (bottom-up approach) • Generic approach to systematics • HFI simulations • Simulations versus data • Systematics Impact Estimates

Power spectra

TBW

Summary of HFI data characteristics

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Overview

The LFI DPC processing is organized into different "Levels": 1,2,3,4 and S. In brief the Level-1 has the scope to analyze the data in a daily base, transform the telemetry packets in to timelines containing engineering values and feed it in the DPC database. Level-2 use the output of the Level-1 transforming raw TOI in to calibrated timelines with all the know systematic sources removed, those timelines are then used in the mapmaking process to create all the possible maps combinations. Level-3 use the Level-2 output of both DPC to derive astrophysical results like Catalogue, CMB map, foreground etc…. Level-S is the common simulation pipeline used to validate the results and any algorithm before its introduction into the official pipeline. Finally the Level-4 just act as a collector pointing used to reformat, document and deliver the products to the final archive.

Level 1: From packets to TOI

Level 1 takes input from the MOC’s Data Distribution System (DDS), decompresses the raw data, and outputs Time Ordered Information for Level 2. This will be done by using software. The input to Level 1 are the telemetry (TM) and auxiliary data as they are released by the MOC (Mission Operation Centre). Level 1 will use TM data for performing a routine analysis (RTA) of the S/C and P/L with the aim of monitoring the overall health of the payload and detecting possible anomalies, and performing a quick-look data 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 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 data from both Sky and Load. These two have to be properly combined to produce differenced data therefore 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 are the removal of know systematic effects and then the photometric calibration where calibrated means essentially that TOD are in physical units instead of engineering units; the following 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 by means of pipeline processing and to provide other data sets including description of astrophysical sources (final catalogue of point sources, extended source maps and catalogues, description of global or statistical properties etc …). Data from both HFI and LFI are analyzed jointly to reach the final expected result. Level-3 processing is described in detail in the L3_LFI and HFI/LFI joint data processing section

Level S : A 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), detectors pointing and beams, generates the infalling power on each detector. It can also provide a simplified description of eg. the noise. It is further described in the HFI/LFI common section.

LFI DPC Infrastructures The LFI DPC provide a centralized hardware and software infrastructure to a large number of geographically distributed institution participating to the Planck mission. In few word the data are interfaced to a database where only meta-information are stored. This allow 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 at the following link Planck early results. V. The Low Frequency Instrument data processing and instrument performances are reported Planck early results. III. First assessment of the Low Frequency Instrument in-flight performance