Hello Randy,
If doing this, please make it clear that by 'Spectral' you mean 'wavelength spectral'. There are other types of spectra, such as frequency (used for wave spectra) and size (used optical plankton counters and other particle sizers).
Cheers, Roy.
Please note that I now work part-time from Tuesday to Thursday. E-mail response on other days is possible but not guaranteed!
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of rhorne at excaliburlabs.com
Sent: 10 April 2013 14:20
To: cf-satellite at unidata.ucar.edu; cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] New CoordinateType: Spectral?
Jonathan:
With the growing interest in the CF conventions around the world by the satellite CF data producer and user communities coupled with the ubiquitous nature of wavelength-based satellite CF data sets, does it make sense to add a paragraph to Section 4 Coordinate Types to discuss Spectral Coordinates ?
very respectfully,
randy
++++
Dear Aleksandar
> I know this will likely end up as a trac ticket but would like first
> to gauge the community's opinion about defining a new coordinate type.
> Satellite data originates as measurements at a number of intervals of
> the electromagnetic spectrum. These intervals are commonly referred to
> as bands or channels. Deciding on how to store the band information is
> one of the key issues toward a standardized representation for
> satellite data.
>
> The convention seems to allow storing of band information either as a
> numerical coordinate variable or as a string auxiliary coordinate
> variable.
Yes, the CF standard could handle both of those, without any modification.
A trac ticket may not be needed. I certainly think there is no problem at
all for a numerical coordinate of band wavelength. You need only to propose
a new standard name for it, if one is needed. There is already a generic
standard name of radiation_wavelength, included for use as a coord variable
just as in your first example. If you need something more specific, I would
suggest sensor_radiation_wavelength. The coord values for this would be the
central wavelengths, and you could also supply bounds specifying the range
of wavelengths covered by the sensor.
Although string-valued auxiliary coordinate variables are possible already,
as used in your second example, I would argue they are less useful as
metadata than numerical ranges. That is because the main use of CF is to
support intercomparison of datasets, which is better-defined if numbers are
used. If there are widely used definitions of named wavelength bands,
required for intercomparison of many datasets, a standard_name could be
defined with a number of permitted string values. I think this extension
could probably be seen as a new standard_name, not requiring a change to
the conventions, although it could be explicitly mentioned in section 6 like
Roy is proposing for biological taxa.
Best wishes
Jonathan
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