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META TOPICPARENT name="WebHome"

PACS instrument and calibration web pages

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  You can also consult the PACS NHSC homepage.
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Temporary notes

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NEW NEW NEW Latest Updates (11-July-2016)

  • HIPE 14.2 has been released
  • PACS instrument data with HIPE 14.2 version will be part of an upcoming bulk reprocessing (Note last bulk of PACS data was performed with 14.0.1)
  • Check calibration updates and improvements
  • Warning for pointing anomaly in HIPE/SPG 13/14: several PACS and SPIRE photometry observations reported are affected by a known problem related to the reset of the Spacecraft Velocity Vector (SVV) during the upload of the star-tracker's defective pixel table. For the affected observations, the pointing of the telescope can be off along the scan direction, and shifted up to 20 arcsec up to 14.0.1
 

Observing with PACS

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PACS spectrometer calibration

  • The PACS Spectrometer pipeline science-ready data (Level2/Level2.5) are calibrated for extended emission.
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  • The calibration of the spectrometer is based on repeated measurements of planets, asteroids, and stars. The RMS scatter of these measurements are just over 10% within any spectral band, about the same when comparing different spaxels, and similar (but higher in the red) when looking for broad-band features within any band. See the PACS Spectrometer Calibration Document for the exact numbers. These calibration certainties are independent, and should be combined when quoting calibration errors.
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  • The calibration of the spectrometer is based on repeated measurements of planets, asteroids, and stars.
 
    • Telescope background model for chop nod: a script to compute the telescope background model calibration tables and a technical note explaining the method used can be found here. Warning: the calibration tables computed with this script are not the same as the ones in the calibration tree. See the technical note for details.
  • Point source observations. To extract and calibrate the spectrum of a point source, it is necessary to use one of the tasks provided: it is not enough to add up the field-of-view of use the central spaxel only. How to do this is documented in the PACS DRG for spectroscopy.
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  • PACS Spectrometer performance and calibration: The PACS Spectrometer Calibration Document v2.4 (16-June-2011) provides details on the calibration accuracy and the necessary information to optimally interpret PACS spectroscopy observations. (Please note, this document refers to the calibration status and performance of pipeline version v8.0. An update compatible with HIPE v14 release will be provided soon.) This includes:
    • flux calibration accuracies for chop nod and unchopped observations
    • the beam efficiencies and the PACS integral field footprint
    • spectral leakages and ghosts
    • wavelength calibration, including information on a skew our native line profile develops as a point source moves off the centre of a spaxel
    • table of the point source correction factors for different wavelengths
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  • PACS Spectrometer performance and calibration: NEW The PACS Spectrometer Calibration Document v3.0 (7-July-2016) provides details on the calibration accuracy and the necessary information to optimally interpret PACS spectroscopy observations.
    • Info Calibration accuracies:
      • The absolute flux error of >100 measurements of different calibration sources is 6-12% in all bands, with a systematic error below 1%. Continuum flux reproducibility from observations on HD 161796 is estimated at 15% (peak-to-peak).
      • Relative flux accuracies within a PACS-S spectral band are:
        • chop nod (Telescope background normalisation): 5% up to 150 μm, and 10% beyond
        • unchopped (calBlock + RSRF): 10% for all wavelengths
 
  • An explanation of the data errors for any particular observation is provided in the PACS Data Reduction Guide for spectroscopy (sec. 7.6)
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  • PACS spectrometer beams: The PACS spectrometer beam efficiencies are maps of the response of each detectors on the sky. They describe the (relative) coupling of a point source to each spaxel as a function of its (the source) position in the FOV.
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  • PACS spectrometer beams: The PACS spectrometer beam efficiencies are maps of the response of each detectors on the sky. They describe the (relative) coupling of a point source to each spaxel as a function of its (the source) position in the FOV.
 
    • Version 6, the most up-to-date, can be directly downloaded in a tar ball PCalSpectrometer_Beam_v6.tar.gz. The corresponding calibration files are named BeamsPerSpaxelXXX, depending on the band.
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    • The PACS beam efficiencies are based on Neptune raster maps at certain (14) wavelengths observed during the mission:
      • Coarse 25x25 raster maps with raster step size 2.5" were obtained between ODs 174 and 751 in chopped mode covering all 25 spaxels.
      • Fine Neptune 5x5 raster maps with raster step size 2 were executed on ODs 1311 and 1312. The combination of four such fine rasters, offset by 1", provide very high sampling for the central spaxel beam efficiency only.
      • All these measurements were registered using least squares minimization in coordinates and gain, and a synthetic beam was constructed with the coarse raster outside the area covered by fine raster and from matched fine raster inside. Finally, this synthetic beam is interpolated into a 0.5" grid.
      • All raster maps were observed with only one chop -off position (aka, asymmetric chopNod).
    • Beam efficiencies are normalised so that a point source of flux 1 at the centre of spaxel 12 has an integral of the instrument response equal to 1.
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    • The WCS associated with the beam is in sky coordinates for position angle 0.
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    • The WCS associated with the beam is in sky coordinates for position angle 0.
 
    • A full history of the PACS Spectrometer beam efficiencies versions can be found in PACSSBeamEfficienciesControlVersion.pdf
    • The raw data from which the PACS spectrometer beams (all versions) have been derived is also available as tables (y, z offset - signal):
      • SpecSpatial_BeamEfficiency_central_spaxel_tables_v1.tar.gz:This contains a FITS file for each wavelength measured for the central spaxel only. Raw data of the coarse and fine rasters are combined. The array dimension of the fits file is [3,npoints] where the first column gives the y raster position, the 2nd column the z raster position and the 3rd column the normalised flux measured at this raster position.
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  The Herschel Science Archive provides bulk-processed Level 2/2.5 products for photometry and spectroscopy.
  • This Data Processing Known Issues page describes typical problems and caveats the observer needs to be familiar when looking at the results of this "SPG" (standard product generation) processing. Aspects of product quality which can be further optimised by interactive processing are also summarised here. The document refers to the version of data processing pipeline currently being used for processing of incoming Herschel data.
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  • For a explanation of PACS products, i.e. what you get when you download a complete or part of an observation from the HSA, see the PACS Products Explained, which can also be found on the HIPE help pages.
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  • For a explanation of PACS products, i.e. what you get when you download a complete or part of an observation from the HSA, see the Info PACS Products Explained, which can also be found on the HIPE help pages.
 
  • PACS data are reduced with pipeline scripts which are a set of command-line tasks that process the data from Level 0 (raw) to Level 2/2.5 (science-ready). There is more than one flavour of pipeline script, tailored to different types of science target, AOT, and observing plan. These 'interactive' pipeline scripts are provided in HIPE and explained in the data reduction guides.
  • The data you get from the the HSA will have been processed by the 'SPG' (Standard Product Generator) using one pipeline script flavour per AOT. Which script is used is documented in the PDRG.
  • The SPG scripts include all the stable pipeline tasks within those scripts, with task settings that correspond to the most common type of science target for each AOT. But some pipeline tasks still can only be run via the interactive pipeline scripts, and to modify the parameter settings for the important pipeline tasks also requires you re-process the data. The Launch Pads (see below) include a guide to understanding the pipeline scripts and how to decide whether to reprocess your data and if so, with which script.
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  • The recommended User Release HCSS (Herschel common science system) version that you should use for reducing PACS data is HIPE v14.2
  • In the CIB (continuous integration build) this version corresponds to Track 14, build 3595. The CIB is the continuously bug-fixed/upgraded/improved version of HIPE, which every few months (in the beginning of the mission) or yearly (in the post-operations phase) becomes a stable User Release.
  • Within HIPE you can access all the PACS data reduction documentation and the general HCSS and HIPE user documentation for Track 14 here. The documentation provided via HIPE opens in a web browser, but for those of you who prefer PDF, we include the PACS Data Reduction Guides as PDF files here (note that within the standalone pdf versions, external links will not work):
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  • The what's new in HIPE 14 page lists the changes in HIPE version 14.2 with respect to the 14.0, and provides a detailed list of updated functionalities, product changes, and calibration aspects.
  • The Data products known issues page details issues about the pipelines or the data products that are known about and offers advice for dealing with them. Consult this if you encounter problems with your data to see if it has already been addressed.
  • Link to the General HCSS Public Twiki page (with general framework information and updates): http://herschel.esac.esa.int/twiki/bin/view/Public/WebHome
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Cookbooks and interactive pipeline scripts

  • The various interactive pipeline scripts PACS photometry and spectroscopy provide in HIPE can be seen as cookbooks, since they take you through each pipeline, task by task, explaining briefly what each task does, commenting on the more crucial pipeline tasks, and showing you how to plot, image, visualise and inspect your data as you work through the pipeline. An example public observation is included with each so you can test it out before using it on your data. These data reduction scripts are available in HIPE under the menu: Pipeline --> PACS --> Photometer/Spectrometer.
  • The PACS Launch Pads are taken from the first chapters of the respective PDRGs and are a useful quick-start guide to loading your data into HIPE, looking at them, and then what to know and do before you begin reprocessing your data with one of the pipelines. From HIPE 14.2:
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    • There we also include:
      • why we recommend you do re-pipeline your data
      • what you need to pay attention to for different types of astronomical source
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  • Calibration certainty: is discussed on this page in the section 'Photometer calibration in scan maps', with links there to two publications. You can also read sec 3.3 of the PACS Observer's Manual
  • Sensitivity: this depends on the AOT, this information is also provided in the AOT Release Notes, and can also be computed by running HSPOT.
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META FILEATTACHMENT attachment="PacsSpectroscopyPerformanceAndCalibration_v3_0.pdf" attr="" comment="PACS Spectrometer Performance and Calibration Document v3.0" date="1467992765" name="PacsSpectroscopyPerformanceAndCalibration_v3_0.pdf" path="PacsSpectroscopyPerformanceAndCalibration_v3_0.pdf" size="1603333" user="ElenaPuga" version="1"
 
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