Hi Karl -
I've only used it the way you describe, but the definition that was
originally
proposed said 'A coordinate variable can be used to specify the
radiation wavelength or frequency.'
I checked some on line definitions, and that seems to be correct. E.g.
wikipedia
says 'When quoted unqualified, it usually refers to some appropriate average
across the spectrum of visible light.' I didn't find any definitions
that ruled
out the use of a specific frequency range.
My change was just to clarify that when a frequency is not specified, we
mean
the 'appropriate average'.
Nan
On 6/19/13 5:18 PM, Karl Taylor wrote:
> 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
>>>>>
--
*******************************************************
* 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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