[CF-metadata] albedo, air pressure definitions

Nan Galbraith ngalbraith at whoi.edu
Fri Aug 7 13:15:06 MDT 2015


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



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