Difference: SpireCalibrationWeb (93 vs. 94)

Revision 942013-09-12 - LucaConversi

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META TOPICPARENT name="WebHome"

SPIRE instrument and calibration web pages

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  Herschel-SPIRE detectors are only sensitive to relative variations, and so as a consequence, the absolute brightness of the observed region is unknown and maps are constructed such that they have zero median. The Planck-HFI detectors are similar to the SPIRE ones, but the Planck observing strategy allowed it to (almost) observe a great circle on the sky every minute (having a 1 rpm spinning rate). By comparing the sky brightness as measured by COBE-FIRAS at the galactic poles (where the dust emission is lower), HFI is capable of setting an absolute offset to its maps. SPIRE and HFI share two channels with overlapping wavebands: SPIRE-PMW and HFI-857 have a similar filter profile, while SPIRE-PLW and HFI-545 are shifted by ~10%.
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As of HCSS 10, a new task named zeroPointCorrection is available: this task calculates the absolute offset for a SPIRE map based on cross-calibration with HFI-545 and HFI-857 maps, colour-correcting HFI to SPIRE wavebands assuming a grey body function with fixed beta. At first, Planck data needed by the task were delivered to HSC under special agreement: as a consequence, Herschel users were not able to re-process the absolute offset calculation. However, Planck data became public in April 2013 and it is now possible to exectue the zeroPointCorrection task.

Files needed:

  • Download the HFI-545 and HFI-857 maps from the HSC/SPIRE FTP area. These maps are derived from the ones available in the Planck Legacy Archive, but convolved with an 8 arcmin Gaussian beam in order to circularize the effective map beams, plus the maps absolute offset as estimated by the Planck-HFI team via cross-calibration with FIRAS (see Planck Collaboration VIII. 2013, In preparation)
  • If you are using HIPE 10.x, download the colour correction table file SpireHfiColourCorrTab_v1.1. This step is not needed if you are using HIPE 11 or later versions as the proper colour correction file is already included in the build.
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As of HCSS 11, a new task named zeroPointCorrection is available to the users: this task calculates the absolute offset for a SPIRE map based on cross-calibration with HFI-545 and HFI-857 maps, colour-correcting HFI to SPIRE wavebands assuming a grey body function with fixed beta. To run the task, you will need to download the 2 Planck maps HFI-545 and HFI-857 maps from the HSC/SPIRE FTP area as they are not included in the HIPE distribution. These maps are derived from the ones available in the Planck Legacy Archive, but convolved with an 8 arcmin Gaussian beam in order to circularize the effective map beams, plus the maps absolute offset as estimated by the Planck-HFI team via cross-calibration with FIRAS (see Planck Collaboration VIII. 2013, In preparation)
  The offsets are computed on extdPxW maps, calibrated for extended emission, with extended gain correction applied and in units of MJy/sr (as explained in the section 5.7 of the SPIRE Data Reduction Guide). Hence, the re-processing will start from a level-1 context (which may be the result of merging multiple observations, see e.g. the Photometry Map Merging scirpt available in HIPE under the menu ScriptsSPIRE Useful script) and then executing the zeroPointCorrection task with one of the following methods:
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  1. If you are using HIPE 10, run the zeroPointCorr_HIPE10.py script. It assumes that the observation has been reduced with HIPE 10 or previous versions. It also sets three required properties needed by the zeroPointCorrection task, i.e. the location of two HFI maps and the colour correction table: please modify the PATH_TO_FILE accordingly to your set-up.
  2. If you are using HIPE 11, run the zeroPointCorr_HIPE11.py script. It assumes that the observation has been reduced with HIPE 11 or later versions. It also sets the location of the two Planck maps by the zeroPointCorrection task: please modify the PATH_TO_FILE accordingly to your set-up.
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  1. Run the zeroPointCorr_HIPE11.py script. It assumes that the observation has been reduced with HIPE 11 or later versions. It also sets the location of the two Planck maps by the zeroPointCorrection task: please modify the PATH_TO_FILE accordingly to your set-up.
 
  1. Alternatively, run the correction using the SPIA interface (SPIRE Photometer Interactive Analysis). In order to be able to run the zeroPointCorrection task, the user.props file present (by default) in you $HOME/.hcss directory must be modified and the following lines added (please modify the PATH_TO_FILE accordingly to your set-up):
    • spire.spg.hfi.545map = PATH_TO_FILE/DX9_map_545_smooth_8arcmin.fits
    • spire.spg.hfi.857map = PATH_TO_FILE/DX9_map_857_smooth_8arcmin.fits
 
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