[CF-metadata] CF names / inherent optical properties in seawater

[Jonathan Gregory]

Dear Frederic

> The inherent optical properties in marine optics, absorption and scattering,
> are the absorptance and scatterance per unit distance in the medium, and
> expressed in m^-1. If they are expressed at a given wavelength (spectral
> quantities), then these quantities are all spectral, but the unit is not
> affected. 

I would argue that the quantity is not really affected either. The difference
is whether it's a broad or a narrow wavelength range, isn't it. If the
wavelength range is restricted, this is indicated by specifying it, using a
coordinate of radiation_wavelength. It seems to me this is rather analogous
to, for instance, temperature at a point versus temperature averaged over an
area.  We use the same standard names for temperature regardless of this
distinction, which is instead indicated by coordinate ranges and cell_methods.

Best wishes

Jonathan