Dear Jonathan,
*About reflectance, the quantity that is usually provided in ocean colour products is the bidirectional reflectance; albedo is of the same nature than reflectance, except that it is integrated on all directions.
In CF there is 'toa_bidirectional_reflectance', which is quite closed to the quantity we are looking for. [Philippe and ocean colour people, of course please tell me if I'm wrong]
Then I would suggest to turn my first proposal into 'surface_bidirectional_spectral_reflectance': with "surface" instead of "toa", and adding "spectral" because this field is provided at several wavelengths. Do you agree?
**About Secchi disk
Yes the intention is primary to provide the depth in meters. So I'd prefer something closed to your second suggestion, like "secchi_depth_of_sea_water".
Best regards,
Olivier.
-----Message d'origine-----
De : Jonathan Gregory [mailto:jonathan at met.reading.ac.uk] De la part de Jonathan Gregory
Envoy? : vendredi 16 octobre 2009 10:44
? : olivier lauret
Cc : cf-metadata at cgd.ucar.edu; Laurence Crosnier; Andrei LINTU; cristina.tronconi at artov.isac.cnr.it; Philippe Garnesson; Ludovic BOURG; Yann BARZIC
Objet : [CF-metadata] Sea water transparency and reflectance.
Dear Olivier
> surface_reflectance (1)
>
> CF already propose `surface_albedo', so from this basis we propose to
> extend it with a less specific quantity.
We've not defined "albedo" in the existing names. I believe it refers to all
incoming radiation, direct beam or diffuse - is that right? Please could you
suggest how reflectance and albedo are distinguished? Also, what does
reflectivity mean, which is a word used in standard names already (in
connection with radar)? Is it different from reflectance.
> *depth_of_disappearance_from_surface (m)
>
> A quantity that is usually known as Secchi disk depth.
>
> I must admit I am not very satisfied with this proposal because the
> first thing that come into our mind is `depth of disappearance of
> what?'.
Thanks for the references. I think it partly depends on what the intention of
the data variable is. My incomplete understanding of the refs that the Secchi
disk may be a way to estimate the quantity with this existing CF standard name:
volume_scattering_coefficient_of_radiative_flux_in_sea_water:m-1
Is that right? If so, could the data be converted into that geophysical
quantity and named accordingly? On the other hand, if the intention is to
record the "raw" measurement, then it may be better to be explicit about this
and name it e.g. secchi_depth_of_sea_water, and leave it to the definition to
explain what it is.
Best wishes
Jonathan
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Received on Mon Oct 19 2009 - 08:38:25 BST
