[CF-metadata] use of volume_* and *_optical_thickness in variable names

From: Jonathan Gregory <j.m.gregory>
Date: Fri, 16 Sep 2011 17:34:00 +0100

Dear Markus

Welcome to CF.

> 1) To what degree are qualifications part of the standard_name? In the guidelines for constructing standard_names, qualifications such as _in_air or _due_to_dry_aerosol are separated from the standard name, while they are included with some standard_names in the table. Would a suitable standard_name be "surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol" or just "volume_scattering_coefficient" with the qualifications optional? Would the qualifications I used in the example be correct?

The qualifications are part of the standard name. So far, we have decided to
approve each qualified standard name individually, although if they follow
existing patterns it is often easy to reach agreement.

> 2) How are the terms _optical_depth and _optical_thickness used? I know there are deep ideological divides about the correct use of these terms, and I don't plan to re-open any possible previous discussions. I only would like to know how these terms are used in the CF convention. I found the standard name atmosphere_optical_thickness_due_to_ambient_aerosol in the standard_name table, and the explanation "The optical thickness is the integral along the path of radiation of a volume scattering/absorption/attenuation coefficient." Is this path meant as the slant path pointing, e.g., from the surface at the sun, or along the vertical axis from the surface through the atmosphere?

I don't recall a previous discussion about this. Perhaps someone with relevant
expertise could comment. It might be that more precise names are needed if you
wish to draw the distinction.

> 3) I found the standard_name "volume_extinction_coefficient_in_air_due_to_ambient_aerosol" in the table. In what sense qualifying is the term "volume_", i.e. how would the "volume_extinction_coefficient" be different from the "extinction_coefficient"?

If I remember correctly, the terminology volume_*_coefficient was adopted
for those with units of m-1, in contrast with those for scattering by a
surface, which are dimensionless, and volume_*_function for those in m-1 sr-1.

Best wishes

Jonathan
Received on Fri Sep 16 2011 - 10:34:00 BST