Hi Jonathan,
Thanks for your email.
Please find below my clarifications which I hope will be of help.
Kd - Diffuse Attenuation Coefficient
Radiance and irradiance are specific radiometric terms in optical oceanography.
One indicates directional light contributions while the other indicates the
integral over a hemisphere of cosine-weighted directional light contributions.
We can agree that in general terms both quantities refer to radiation. However,
when we speak of Kd it specifically describes the attenuation of downward
irradiance as a function of depth below the sea surface. So it only refers
to a given radiometric quantity (i.e., it only refers to downward irradiance
and not to radiance, for instance).
CDOM - Colour Dissolved Organic Matter
The reason for adding coloured is only justified by the willingness to comply
with current oceanographic terminology (actually the term to be used is chromophoric).
In any case this is an absorption coefficient (inherent optical property),
it is not specifically referred to irradiance.
But if you think 'Colour' arises confusion I am happy to leave the term out.
Lr -
Lr is a component of total upwelling radiance above the sea surface Lt. This
component accounts for Lr plus Lw, where Lw refers to what comes from below
the sea surface.
Please let me know if you need any further information.
Best Regards,
Pepe
>Date: Sat, 5 Nov 2005 19:49:17 +0000
>From: Jonathan Gregory <j.m.gregory at reading.ac.uk>
>To: "Pepe S. D. Juevara" <sdj at tiscali.it>
>Cc: cf-metadata at cgd.ucar.edu, keith.williams at metoffice.gov.uk,
> Godin at mbari.org
>Subject: RE: agreed standard names
>
>
>Dear Pepe
>
>Thanks for your email. Unfortunately I don't understand the distinctions
>you
>are making! Please could you help again with this.
>
>volume_attenuation_coefficient_of_downwelling_radiation_in_sea_water:m-1
>> Kd - Diffuse Attenuation Coefficient
>> volume_attenuation_coefficient_of_downwelling_irradiance_in_sea_water:m-1
>> This is important since Kd is a measure of 'irradiance' attenuation and
>not
>> of 'radiation'
>We haven't used the word "irradiance" in standard names. "Irradiance" means
>radiative flux (per unit area). I assumed that the attenuation coefficient
>of
>radiation could not refer to anything other than radiative flux or something
>proportional to it. Is there another possible interpretation?
>
>> CDOM - Colour Dissolved Organic Matter
>> volume_absorption_coefficient_of_radiation_in_sea_water_due_to_coloured_dissolved_organic_matter:m-1
>> This is important since it is only the 'coloured' component which we are
>> interested in.
>What does "coloured" mean? Perhaps it means having a wavelength-dependent
>attenuation coefficient? i.e. are you excluding absorption which does not
>change the colour of incident white light?
>
>I notice that you don't propose that this "radiation" should be changed
to
>"irradiance"/"radiative flux" - what's the difference from the last point?
>
>surface_upwelling[_spectral]_radiance_in_air_reflected_by_sea_water:W m-2
>sr-1
>> Lr -
>> surface[_spectral]_sky_radiance_in_air_reflected_by_sea_water: W m-2 m-1
>> sr-1
>> This clarification is important since from your proposed name it seemed
>that
>> Lr was a measure of the reflected scattered radiation but Lr is instead
>a
>> measure of the reflected sky radiance.
>From what Mike said I understood Lr to be the portion of the upwelling
>radiation which came from reflection by the sea-water surface of downwelling
>radiation. The remainder of the upwelling radiation is that which comes
out
>through the surface of the sea water. Are you making a further distinction
>between "sky" and other downwelling radiation? I'm not sure which "scattered"
>radiation you are referring to.
>
>> is the CF policy to use only SI units ? I am asking this since some
>> quantities are never expressed in SI units.
>
>The units stated in the standard name table are "canonical" units. Any unit
>which is dimensionally equivalent (SI or not) is acceptable. See section
>3.3
>of the CF standard.
>
>Best wishes
>
>Jonathan
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Received on Mon Nov 07 2005 - 08:33:09 GMT
