[CF-metadata] attentuation and radiance

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 10 Oct 2005 23:13:11 +0100

Dear Pepe and Michael

> Lw: Water Leaving Radiance:
> above_surface_spectral_radiance_leaving_the_sea_water: W m-2 m-1 sr-1
> above_surface_radiance_leaving_the_sea_water: W m-2 sr-1
>
> The change is necessary as the term 'upwelling' you suggested refers to 'Lu'
> rather than to 'Lw'.

I'm sorry, I don't really understand this. Do you that by "above surface" that
it's the upwelling radiance measured in air? If so we should call them

surface_upwelling_spectral_radiance_in_air:W m-2 m-1 sr-1
surface_upwelling_radiance_in_air:W m-2 sr-1

> Kd: Diffuse Attenuation Coefficient
> volume_attenuation_coefficient_of_downward_irradiance_in_sea_water: m-1
>
> What Michael proposes is in oceanography referred to as "C", "Beam
> Attenuation Coefficient" which is an inherent optical property and is not
> the same quantity as Kd.

Ah, I see. I appreciate that "diffuse" is a commonly used term for
attenuation which is not "beam", but this is potentially confusing, I suspect,
because "diffuse" might be understood to *exclude* the direct beam. The
distinction between these two is that "beam" refers to attenuation per unit
distance along the direction of travel of light, and "diffuse" per unit
distance in some arbitrarily chosen direction, considering light from all
directions. Hence I suggest

volume_attenuation_coefficient_of_downwelling_radiation_in_sea_water: m-1
volume_beam_attenuation_coefficient_of_radiation_in_sea_water: m-1

for "diffuse" and "beam" respectively. The latter does not need "downwelling"
because it is by definition along the beam. I propose "downwelling" instead of
"downward" for consistency with other radiation standard names. Both need
"volume" because they could alternatively be "specific" in m2 kg-1.

Is this all right with both of you? I presume that the scattering and
absorption coefficients are always "beam", are they?

Cheers

Jonathan
Received on Mon Oct 10 2005 - 16:13:11 BST