Dear Maarten,
Thank you for your proposals. I have now created entries for them in the standard names editor at
http://cfeditor.ceda.ac.uk/proposals/1?status=active&namefilter=&proposerfilter=Maarten&descfilter=&unitfilter=&yearfilter=&filter+and+display=Filter, so they certainly will not be lost. (At the moment they appear with blue headings to indicate that they are new proposals - I wanted to demonstrate this feature of the editor - but I will shortly change their status to "Under Discussion"). By proposing your names to the list they are already "in the process" so now it is a case of responding to any further comments as they arise. Names are formally accepted when consensus has been reached on the terms themselves, the definitions and units. Once accepted, they are automatically included in the next update of the standard name table.
I have given my detailed comments on the individual proposals and your additional questions below.
1. toa_incoming_photon_solar_irradiance_per_unit_wavelength
I agree with Jonathan's comment that "solar" is not really necessary and you have indicated that it is OK to remove it, so we would then have
toa_incoming_photon_irradiance_per_unit_wavelength.
Taking your own definition and adapting the wording slightly for consistency with existing "toa_incoming" and "irradiance" names I arrived at the following:
"toa" means top of atmosphere. The TOA incoming photon irradiance is the photon flux from the sun on a surface perpendicular to the incoming radiation i.e. the "downwelling" flux. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A coordinate variable for radiation wavelength should be given the standard name radiation_wavelength. A photon flux is specified in terms of numbers of photons expressed in moles.
Canonical unit: mol m-2 m-1 s-1
As it stands, this looks fine and could probably be accepted for inclusion in the standard name table straight away. However, you included some notes about the coordinate variable and unit which need some further consideration. I'll address the units issues first, as these are the easiest to answer!
On 12/11/14 Maarten wrote:
> Note 3: mole as a unit for counting photons is unconventional within the
> satellite community, photon fluxes are typically expressed in 'photons
> cm-2 nm-1 s-1' and 'photons cm-2 nm-1 s-1 sr-1'. It would be nice to add
> 'photon' as an alias to UDUnits, in a way that is similar to the recent
> addition of 'molecule'.
UDUnits is not under the control of the CF community, however we could request a unit of photon to be added to the database if that seems the best way forward. The unit 'molecule' was requested in response to a series of proposals for column trace gas standard names, such as troposphere_mole_content_of_formaldehyde. In the discussion of those names we agreed that the canonical unit should remain as mol m-2 and asked for molecule to be added to UDunits - this allows users to write "molecule" in their files and UDunits can then convert back to the canonical unit.
Following the same approach, I would advocate that the canonical units of your proposals should continue to be expressed using 'mole' but if photon were added to UDunits you could use it in your files. The 'molecule' entry in UDUnits is expressed as follows:
<unit>
<def>mol/6.02214129e23</def>
<!-- NIST 20130402 -->
<name>
<singular>molecule</singular>
</name>
<aliases>
<name>
<singular>molec</singular>
</name>
<name>
<singular>nucleon</singular>
</name>
<name>
<singular>nuc</singular>
</name>
</aliases>
</unit>
It looks as though we would simply need to request an additional alias of 'photon' for the existing definition of mol/6.02214129e23. Do you agree?
On 12/11/14 Maarten wrote:
> Note 4: Other instruments may use other units, depending on the
> construction of the instrument. These can not be converted easily into
> one another as they require additional knowledge, in particular
> knowledge of the wavelength. I'm unsure if UDUnits is equiped to handle
> these types of conversion. Additional names may be needed for using "W
> m-2 m-1" or "W m-2 m-1 sr-1" respectively (similar name, but leaving out
> the 'photon') Another quantity that is commonly encountered expresses
> the radiation_wavelength as wavenumber or frequency, and therefore also
> alters the (frequency/energy) interval over which the quantity is
> integrated. I'll leave the addition of these quantities to communities
> that actually use them, IASI on MetOp comes to mind.
It is accepted CF practice that different units for similar quantities, where conversion is not simply a matter of scaling, require different standard names. An existing example would be the ozone quantities
equivalent_thickness_at_stp_of_atmosphere_ozone_content (canonical unit of metres)
and
atmosphere_mole_content_of_ozone (canonical unit of mol m-2).
It is also accepted practice that we do not create new standard names unless someone actually needs to use them, so I think you are correct that other communities should propose the additional names as and when they are required.
On 12/11/14 Maarten wrote:
> Note 1: The coordinate variable for radiation wavelength may require a
> mapping that is similar to the mapping of geolocation coordinates for
> satellite observations, i.e. not a dimension, but a multi dimensional
> mapping. This is the case for the OMI instrument, where a 2D-dectector
> is used for wavelength (columns of CCD) and a spatial dimension across
> the swath (rows of CCD). The mapping is imperfect, and the wavelength
> depends on the row-index.
I don't think we have encountered this type of data product before! The question of how to deal with the coordinate variables should not necessarily delay agreement of the standard name as coordinates are more properly in the realm of the main CF Conventions document. If writing your data will require coordinate variables to be treated in a new way then it would be necessary to propose a modification to the conventions as well as proposing the standard name.
Certainly the conventions already allow 2D coordinate variables for use with geospatial grid mappings, but I don't think we have ever had a situation where one dimension is wavelength and the other a location. If I understand you correctly, the wavelength of a single data value also depends on where in the swath the observation was taken. Is that right? Is this because the instrument is scanning through a range of wavelengths as the satellite moves along its track? If so, I am wondering if it might be possible to get around this by using a spatial coordinate variable and also a radiation_wavelength auxiliary coordinate variable on the same dimension of the data. Would that work? How many spatial dimensions are there in your data product? I'd welcome input from anyone else who can help with this issue.
2. toa_outgoing_photon_radiance_per_unit_wavelength
Putting together your own definition with existing definitions of photon_radiance names I arrived at the following:
"toa" means top of atmosphere. Photon radiance is the photon flux in a particular direction, per unit of solid angle. The direction from which it is coming must be specified, for instance with a coordinate of zenith_angle. If the radiation does not depend on direction, a standard name of isotropic radiance should be chosen instead. A photon flux is specified in terms of numbers of photons expressed in moles. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A coordinate variable for radiation wavelength should be given the standard name radiation_wavelength.
Canonical unit: mol m-2 m-1 s-1 sr-1
Is this OK?
My earlier comments on units and coordinate variables apply to this name also. If necessary, we can start a new thread on the mailing list to discuss the coordinate issue more thoroughly.
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
> -----Original Message-----
> From: Maarten Sneep [mailto:maarten.sneep at knmi.nl]
> Sent: 25 November 2014 17:41
> To: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] standard names for surface aerosol optical
> properties
>
> On 25-11-14 18:26, alison.pamment at stfc.ac.uk wrote:
>
> > I would like to publish an update to the standard name table within
> > the next week, concentrating on aerosol names. I will then begin
> > preparation of another update which will focus mainly on remote
> > sensing names, but will also include some other, smaller sets of
> > proposals that have been agreed recently.
> >
> > 5 of the 20 proposals have been accepted for publication in the
> > standard name table. The other 15 remain under discussion. Detailed
> > comments on the individual names are given below. The proposals can
> > also be viewed in the CF names editor at:
> >
> http://cfeditor.ceda.ac.uk/proposals/1?status=active&namefilter=&propos
> erfilter=Markus&descfilter=&unitfilter=&yearfilter=&filter+and+display=Filt
> er.
> > Names with an amber title bar are accepted for publication and will
> > appear in the next version of the standard name table. Names with a
> > title bar that appears greenish/brownish (depending on your display
> > screen) are still under discussion. Below the title bar of each name
> > and at the right of the screen you will also see a coloured label
> > which indicates whether the proposal relates to a new name, creation
> > of an alias (term change), or an updated definition.
>
> Hi,
>
> I tried to fiend my own recent proposal for a standard_name for radiance
> and irradiance in the CF names editor. I din't find them, and want to
> make sure they don't disappear.
>
> The message was sent to this list on Wed, 12 Nov 2014 18:32:34 +0100,
> with subject "Proposal for standard names: radiance and irradiance as
> measured from satellite". Proposed names:
> toa_incoming_photon_solar_irradiance_per_unit_wavelength and
> toa_outgoing_photon_radiance_per_unit_wavelength.
>
> So far there has been one comment by Jonathan Gregory, questioning the
> wisdom of including 'solar' in the name. I'm flexible, and a less
> specific name is fine with me.
>
> Do I need to take different actions to start the process?
>
> Best,
>
> Maarten Sneep
> --
> KNMI
> T: 030 2206747
> E: maarten.sneep at knmi.nl
> R: A2.14
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Received on Wed Nov 26 2014 - 09:52:50 GMT
