Folks:
In the past few months there have been three standard_names proposed related to radiance or irradiance quantities at the top of the atmosphere derived from data sensed by a satellite. The proposals are as follows:
(a)
Message subject: cf-satellite Digest, Vol 29, Issue 1 from Peter Miu
standard_name: toa_spectral_irradiance with canonical units mW m-2 (cm-1)-1
Definition:
Irradiance which is relevant for any sensor measuring in the UV-VIS and NIR. This parameter is reported by integrating over the whole sphere.
(b)
Message subject: cf-satellite Digest, Vol 29, Issue 1 from Peter Miu
standard_name: toa_outgoing_inband_radiance with canonical units mW m-2 sr-1
Definition: "outgoing" means emitted toward outer space; the radiance is integrated over a discrete band.
(c)
Message subject: [CF-metadata] New Standard Names for Satellite Data from Aleksandar Jelenak
Standard_name: toa_outgoing_spectral_radiance with canonical units mW m-2 sr-1 (cm-1)-1
Definition: "toa" means top of atmosphere; "outgoing" means emitted toward outer space "spectral" means per unit wavenumber or as a function of wavenumber. Radiance is the radiant power per unit area in a particular direction per unit of solid angle.
The prefixes "toa" and "outgoing" identified in the CF standard name guidelines are applicable.
The overarching consistency issue of the quantities revolves around their units. For both radiance and irradiance, there are four types of potentially reported quantities where the mappings between them is not trivial, and, more specifically, not supported with a CF standard name modifier or cell_method. The types of quantities are as follows with a focus only on the contrasting characteristics (in a given direction per unit area & per unit solid angle are omitted):
1) Power integrated over all wavelengths.
2) Power at a discrete monochromatic wavelength.
3) Power integrated over a discrete bandpass.
4) Power per unit wavelength integrated over a discrete bandpass and normalized by the bandpass response function (i.e. the spectral response of the sensor).
Given .
* The four types of radiance & irradiance quantities identified immediately above.
* The need to conform with existing applicable CF standard name conventions, specifically the prefixes "toa" and "outgoing".
* The fact that 2) & 4) immediately above are spectral quantities.
* The need to capture the frequency band associated with the radiance/irradiance quantity for 3) & 4) immediately above.
. results in the following standard_names, and "strawman" definitions and canonical units for the four radiance quantities. Note that we have leveraged the work done by Peter and Aleksander.
++++++
#1
standard_name: toa_outgoing_radiance
Definition: "toa" means top of atmosphere. "outgoing" means emitted toward outer space. This quantity is the radiant power per unit area in a given direction per unit solid angle integrated over all wavelengths.
Canonical units: W m-2 sr-1
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#2
standard_name: toa_outgoing_spectral_radiance
Definition: "toa" means top of atmosphere. "outgoing" means emitted toward outer space. "spectral" means per unit wavenumber or as a function of wavenumber. Radiant power per unit area in a given direction per unit solid angle at a discrete monochromatic wavelength.
Canonical units: mW m-2 sr-1 (cm-1)-1
Note: A coordinate variable to capture the wavelength may be used.
***This quantity and its standard_name are identical to that proposed by Aleksander. See c) above. ***
+++++
#3
standard_name: toa_outgoing_inband_radiance
Definition: "toa" means top of atmosphere. "outgoing" means emitted toward outer space. "inband" means the radiance quantity is for a discrete bandpass. This quantity is the radiant power per unit area in a given direction per unit solid angle integrated over a discrete bandpass.
Canonical units: W m-2 sr-1
Note: A coordinate variable to capture the center wavelength, and potentially, a boundary variable to capture the bandpass extents may be used.
***This quantity and its standard_name are identical to that proposed by Peter. See b) above. ***
+++++
#4
standard_name: toa_outgoing_inband_spectral_radiance
Definition: "toa" means top of atmosphere. "outgoing" means emitted toward outer space. "inband" means the radiance quantity is for a discrete bandpass. "spectral" means per unit wavenumber or as a function of wavenumber. This quantity is the radiant power per unit area in a given direction per unit solid angle per unit wavelength integrated over a discrete bandpass and normalized by the bandpass response function.
Canonical units: mW m-2 sr-1 (cm-1)-1
Note: A coordinate variable to capture the center wavelength, and potentially, a boundary variable to capture the bandpass extents may be used.
+++++
There are analogous standard_name for the irradiance values. They are not included in this email to keep the material in as "bite size chunks" as possible in an effort to get some feedback.
very respectfully,
randy
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Received on Wed Apr 03 2013 - 09:28:56 BST
