Dear Nan,
I'm not positive about this, but I thought albedo always referred to the
total fraction reflected (integrating over all shortwave wavelengths and
all angles). If you want to limit it to only a portion of the shortwave
spectrum, I think a different term (reflectivity? reflectance?) should
be used.
Karl
On 6/19/13 8:32 AM, Nan Galbraith wrote:
> 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
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>> ----- End forwarded message -----
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>>
>
>
> --
> *******************************************************
> * Nan Galbraith Information Systems Specialist *
> * Upper Ocean Processes Group Mail Stop 29 *
> * Woods Hole Oceanographic Institution *
> * Woods Hole, MA 02543 (508) 289-2444 *
> *******************************************************
>
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