Can we also update the definition for surface_albedo now? It's currently
' The surface
called "surface" means the lower boundary of the atmosphere.' which
doesn't quite
capture the concept.
We use a (constant, inferred) albedo in our surface flux calculations,
and I'm
planning to include it as a variable when I start publishing those
files in CF.
I'd like to see one detail added to the definitions below, that the
outgoing energy in
the ratio is reflected - not that I can think of another source of
outgoing energy off
the top of my head ...
For example, the ESR glossary says: 'Albedo is the fraction of solar
energy (shortwave
radiation) reflected from the earth back into space. It is a measure of
the reflectivity
of the earth's surface' - so we could use something like
'Albedo is the ratio of outgoing reflected energy to incoming energy
(irradiance).'
Also, should we add the default frequency, for cases where no coordinate
is supplied?
'A coordinate variable can be used to specify the radiation wavelength
or frequency; the default frequency is anappropriateaverage across
the spectrum of visible light.'
(Note, the 'appropriate average' term is used in several descriptions)
Thanks -
Nan
On 5/18/13 10:42 AM, Jonathan Gregory wrote:
> Dear Ted
>
> That looks fine to me. It'd be interesting to know if anyone else has comments.
>
> Thanks
>
> Jonathan
>
> ----- Forwarded message from Ted Kennelly <ekennell at aer.com> -----
>
>> Date: Mon, 13 May 2013 18:01:03 -0400
>> From: Ted Kennelly <ekennell at aer.com>
>> To: Jonathan Gregory <j.m.gregory at reading.ac.uk>
>> Subject: Re: [CF-metadata] New reflectance standard names
>>
>> Below are the updated descriptions for the two proposed standard
>> names. Note CF does not seem to have a definition for albedo though
>> it is used
>> in a handful of standard_names.
>>
>> -ted
>>
>>
>> toa_lambertian_equivalent_albedo
>>
>> Albedo is the ratio of the outgoing to the incoming power per unit
>> area (irradiance). A coordinate variable can be used to specify the
>> radiation wavelength or frequency. toa means top of atmosphere.
>> lambertian_equivalent means the quantity is evaluated for a
>> diffusely reflecting surface.
>>
>> canonical units = 1
>>
>>
>>
>>
>> toa_lambertian_equivalent_albedo_multiplied_by_cosine_solar_zenith_angle
>>
>> Albedo is the ratio of the outgoing to the incoming power per unit
>> area (irradiance). A coordinate variable can be used to specify the
>> radiation wavelength or frequency. toa means top of atmosphere.
>> lambertian_equivalent means the quantity is evaluated for a
>> diffusely reflecting surface.
>> multiplied_by_cosine_solar_zenith_angle means that the quantity
>> has normalized to remove the angular dependence of the incoming
>> shortwave irradiance
>>
>> canonical units = 1
>>
>>
>> Jonathan Gregory wrote:
>>> Dear Ted
>>>
>>> Thanks for this explanation:
>>>
>>>> Reflectance is the ratio of outgoing radiance to incoming irradiance
>>>> giving it units of per steradians.
>>>> Albedo is the ratio of outgoing irradiance to incoming irradiance
>>>> and is unitless.
>>>> Because the proposed quantity is unitless, albedo is the better term.
>>>> However, albedo is the integral over all angles of the bidirectional
>>>> reflectance. In general, true
>>>> planetary albedo would account for this angular dependence. To make clear the
>>>> assumption regarding the Lambertian surface I still propose using the term
>>> Lambertian equivalent in the name. Thus:
>>>
>>>> toa_lambertian_equivalent_albedo
>>>> toa_lambertian_equivalent_albdeo_multiplied_by_cosine_solar_zenith_angle
>>> OK, with small L in lambertian as you had before (because stdnames are all
>>> in lower case). Thanks!
>>>
>>> Cheers
>>>
>>> Jonathan
>>> _______________________________________________
>>> CF-metadata mailing list
>>> CF-metadata at cgd.ucar.edu
>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
> ----- End forwarded message -----
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
--
*******************************************************
* Nan Galbraith Information Systems Specialist *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 (508) 289-2444 *
*******************************************************
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.cgd.ucar.edu/pipermail/cf-metadata/attachments/20130619/93419160/attachment-0001.html>
Received on Wed Jun 19 2013 - 09:32:22 BST
