[CF-metadata] albedo, air pressure definitions

From: Karl Taylor <taylor13>
Date: Fri, 07 Aug 2015 12:34:02 -0700

Hi all,

the proposed definition of albedo doesn't mention that the photons
included in the calculation are emitted by the sun. Radiation
originating at the surface or in the atmosphere ("longwave"), is not
included in the fluxes considered.

regards,
Karl

On 8/7/15 12:15 PM, Nan Galbraith wrote:
> Hi All, and happy Friday.
>
> It's been almost a month since Maarten Sneep posted 'A few definitions
> seem off'
> and there have been just a couple of replies.
>
> Can we please add definitions for albedo and air_pressure to the
> standard names
> table? Do people think we don't need these defined - is that the problem?
>
> I have no particular preference about the content of the definitions,
> here's what's
> been proposed.
>
> albedo:
> 'Albedo is the ratio of the radiant flux exiting a reference surface
> into the whole hemisphere
> to the radiant flux incident on the same surface from the hemisphere.
> The albedo, also called
> the bihemispherical reflectance, is often the ratio of upwelling flux
> to downwelling flux at a
> horizontal surface, such as the reflected and incident radiation at an
> interface.'
> or maybe ...
> 'Albedo is the ratio of reflected radiation from the surface to
> incident radiation upon it.'
>
> air_pressure:
> 'air pressure is the pressure that exists in the medium of air'.
> or ...
> something better ???
>
> Thanks -
> Nan
>
> PS- Ian, I'm not sure what you mean by 'the need to specify the
> reference level' in your
> email below. Sadly no time to look up the reference ...
>
> On 7/27/15 2:27 AM, Ian Grant wrote:
>> Hi Nan,
>>
>> Regarding your proposed definition of albedo: 'Albedo is the ratio of
>> reflected radiation from the surface to incident radiation upon it'.
>> This is essentially correct.
>>
>> However, you and others might want to consider a more thorough
>> definition:
>> 'Albedo is the ratio of the radiant flux exiting a reference surface
>> into the whole hemisphere to the radiant flux incident on the same
>> surface from the hemisphere.'
>> To make it even clearer and more complete, this could be added:
>> 'The albedo, also called the bihemispherical reflectance, is often
>> the ratio of upwelling flux to downwelling flux at a horizontal
>> surface, such as the reflected and incident radiation at an interface.'
>>
>> My definition is adapted from Schaepman-Strub et al. (2006, '
>> Reflectance Quantities in Optical Remote Sensing: Definitions and
>> Case Studies', Remote Sensing of Environment, 103, 27-42,
>> doi:10.1016/j.rse.2006.03.002).
>>
>> The need to specify the reference level is discussed in the
>> introduction to Pinty et al. (2005, 'Coupling Diffuse Sky Radiation
>> and Surface Albedo', Journal of the Atmospheric Sciences, 62 (7),
>> 2580-2591).
>>
>> Regards,
>> Ian
> Hi all -
>
> I thought I should re-post this with a more clear subject line, in case
> anyone else wants to to weigh in on the definitions, or lack
> thereof, of albedo and air pressure.
>
> Are these self-describing enough that they don't need to be
> defined in CF? Or should we add at least a minimal definition?
>
> Thanks -
> Nan
>
> On 7/14/15 3:22 PM, Nan Galbraith wrote:
> Thanks for raising this, Maarten; we should fix the albedo
> definitions. I use
> surface_albedo regularly, but didn't actually have a definition handy,
> so went
> googling.
>
> This one's from wikipedia:
>
> Albedo is the ratio of reflected radiation from the surface to incident
> radiation upon it. Its dimensionless nature lets it be expressed as a
> percentage and is measured on a scale from zero for no reflection of
> a perfectly black surface to 1 for perfect reflection of a white surface.
>
> This one's from ESR.org (earth and space research) and is narrower,
> specific
> to earth's surface:
>
> 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.
>
> I propose we could add the sentence 'Albedo is the ratio of reflected
> radiation from
> the surface to incident radiation upon it' - or something similar - to
> all 3 albedo
> definitions.
>
> For air_pressure_at_cloud_top, well, the definition of air_pressure is
> 'No help available.'
> so I guess that's a problem.
>
> If we use sea_water_pressure as an example, here's that definition:
> '"Sea water pressure" is
> the pressure that exists in the medium of sea water.' True enough.
>
> Cheers - Nan
>
>
> On 7/10/15 10:47 AM, Maarten Sneep wrote:
>> Hi,
>>
>> I came across a few descriptions in the standard name list that seem
>> 'off', or clearly unclear.
>>
>> surface_albedo: "The surface called "surface" means the lower
>> boundary of the atmosphere." (this doesn't define albedo itself).
>>
>> planetary_albedo: "No help available."
>>
>> cloud_albedo: "The albedo of cloud." (this doesn't define albedo
>> itself either, and is not very specific).
>>
>> air_pressure_at_cloud_top: "cloud_top refers to the top of the
>> highest cloud." (This apears very much a modelled parameter, not a
>> parameter from some remote sensing technique. Either the description
>> is kept deliberately vague, or I miss something. It is hard to use
>> this description on observations).
>>
>> I'm sure there are more, but these caught my eye. I'm not sure how to
>> change the descriptions, I don't know the history of these quantities
>> in the standard name list. Can someone advise how to proceed?
>>
>> Best,
>>
>> Maarten Sneep
>
>
>
Received on Fri Aug 07 2015 - 13:34:02 BST