Difference between revisions of "The LFI DPC"
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Revision as of 20:56, 17 March 2013
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.
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 Power Spectra 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 joint data processing.
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.
(Planck) Low Frequency Instrument
Data Processing Center
Cosmic Microwave background
[ESA's] Mission Operation Center [Darmstadt, Germany]
MOC's Data Distribution System
(Planck) High Frequency Instrument
Planck Sky Model