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Knowledgebase : Calibration > Calibration - SPIRE
Reduction and analysis of SPIRE FTS spectra treats two, generic cases: point sources (sources smaller than 3-4 arcseconds that are effectively a point-source for SPIRE) and extended sources (anything larger than 40 arcseconds). However, there are many sources between these two extremes that can neither be treated as point sources, nor as extended. The immediate consequence for observers is that neither the point source reduction, nor the extended source reduction give a good result: users will see this in the form of a large discontinuity between the two SPIRE spectra ranges.
There is a Herschel Science Centre short videotutorial that shows you how to categorise sources by diameter and how to identify cases in which neither the point source calibration, nor the extended source calibration give a satisfactory result and how to treat these cases. You can find it here:
https://www.youtube.com/watch?v=mxZpHgHVtP4
The short videotutorial will walk you through the basics of SPIRE FTS spectra data reduction, including the need to carry out certain, basic pre-reduction such as to subtract the background first before applying the Semi-Extended Calibration Tool (SECT) to the spectra. It will show you how to set the parameters and, through a practical example, how to make an iterative fit to the effective source diameter. Finally, it will show you the checks that you can carry out to ensure a self-consistent result.
Answer supplied by Ivan Valtchanov:
To do the conversion, you should use the pipeline beam area as provided in the SPIRE Data Reduction Guide, table 6.7, i.e. (465.35, 831.27, 1804.31) arcsec^2 at (250, 350, 500) microns, in order to convert your image from Jy/beam to Jy/pixel.
Within the Herschel Interactive Processing Environment (HIPE): you can use the task, convertImageUnit():
newImage = convertImageUnit(image=my250_image_in_Jy_per_Beam, newUnit='Jy/pixel',beamArea=465.35)
You can find out more about this process in the useful Herschel Science Centre short videotutorial on SPIRE Photometer: Aperture photometry. You can find the videotutorial, here:
https://www.youtube.com/watch?v=fjzf-VN_X0s
Answer supplied by David Teyssier:
The calibration uncertainties vary from one instrument to another. A summary of those is provided in each of the instrument overview pages, namely:
HIFI: https://www.cosmos.esa.int/web/herschel/hifi-overview
PACS: https://www.cosmos.esa.int/web/herschel/pacs-overview
SPIRE: https://www.cosmos.esa.int/web/herschel/spire-overview
The calibration uncertainties are provided in the Performance and Calibration section, typically with a distinction between absolute and relative (repeatability) accuracy. For HIFI a dedicated calibration uncertainty budget table exists per observation, and can be retrieved as an HPDP - see https://www.cosmos.esa.int/web/herschel/highly-processed-data-products.
The Herschel Science Centre has produced a number of short videotutorials about the analysis of data with the Herschel instruments. These contain information on the uncertainties in photometry and on the flux calibration of spectroscopy and how to treat the different effects that may influence it. You can find the videotutorials, which we recommend strongly viewing, here:
https://www.cosmos.esa.int/web/herschel/legacy-training-materials
The Herschel Science Centre has produced two simple, step-by-step guides for anyone who would like to perform photometry on a SPIRE image. These give details of how to perform photometry and the corrections that must be performed on the raw photometry.
The first short videotutorial explains how to perform aperture photometry on SPIRE maps and gives an overview of the corrections that are required, If you are familiar with SPIRE photometry, you can pass straight to the second video, although we recommend that users watch both:
https://www.youtube.com/watch?v=fjzf-VN_X0s
The second short videotutorial explains in more detail the steps in applying corrections to the raw photometry, in particular, the sequence of the corrections to apply and how to apply the colour correction to SPIRE photometry are explained. This videotutorial shows practical examples of applying the corrections to real data from SPIRE:
https://www.youtube.com/watch?v=i98LQWEwd8I
Answer supplied by Ivan Valtchanov:
The SPIRE beams for both the Photometer and Spectrometer are available as ancillary data products (ADP) in the Herschel Legacy Area:
http://archives.esac.esa.int/hsa/legacy/ADP/PSF/SPIRE
For the SPIRE Spectrometer in sub-folder SPIRE-S and in subfolder SPIRE-P for the Photometer.
The SPIRE beams are also are available within the calibration tree and can be accessed using the Herschel Interactive Processing Environment.
You can also obtain the Photometer beam data by going to the release note:
http://archives.esac.esa.int/hsa/legacy/ADP/PSF/SPIRE/SPIRE-P/README.html
For the spectrometer, the release not is here:
http://archives.esac.esa.int/hsa/legacy/ADP/PSF/SPIRE/SPIRE-S/README.html
Observations with SPIRE Spectrometer before OD189 (19 Nov 2009) have not been made public as the detector parameters before that date were not at their final values. Many observations, even those performed using standard astronomer observing templates (AOT), are at different bolometer settings and although the pipeline can run in principle, the calibration is not adapted for those non-optimal parameters. That is why we cannot release this observation to the public, because people will end up with a nice looking spectra or spectral maps, which are not properly calibrated.
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