Hi all,
I hereby propose the addition of the following standard names. All are
commonly used quantities used in passive satellite remote sensing, to be
specific instruments that use ultra-violet, visible and near infra-red
radiation for remote sensing of atmospheric composition, sometimes
including wavelengths up to 2.5 micrometer (shortwave radiation).
Examples of these instruments include GOME, SCIAMACHY, OMI, GOME-2,
OMPS, and the upcoming TROPOMI on Sentinel 5 precursor, and instruments
on Sentinel 4 and Sentinel 5 missions.
Please note the notes at the end.
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* toa_incoming_photon_solar_irradiance_per_unit_wavelength
"toa" means top of atmosphere. "Photon solar irradiance" is the photon
flux on a surface perpendicular to the incoming solar radiation. The
direction is specified as "incoming". A photon flux is specified in
terms of numbers of photons expressed in moles. The "per unit
wavelength" indicates a spectrally resolved quantity. A coordinate
variable for radiation wavelength should be given the standard name
radiation_wavelength.
Canonical unit: mol m-2 m-1 s-1
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* toa_outgoing_photon_radiance_per_unit_wavelength
"toa" means top of atmosphere. "Photon radiance" is the photon flux in a
particular direction, per unit of solid angle. The direction is
specified as "outgoing", i.e. radiation from below. A photon flux is
specified in terms of numbers of photons expressed in moles. The "per
unit wavelength" indicates a spectrally resolved quantity. 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
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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.
Note 2: Existing standard names supply aliases for these names:
"toa_incoming_spectral_photon_solar_irradiance" and
"toa_outgoing_spectral_photon_radiance" respectively.
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'.
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.
Kind regards,
Maarten Sneep
--
KNMI
E: [email protected]
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