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

From: Markus Fiebig <Markus.Fiebig>
Date: Tue, 6 Sep 2011 13:07:48 +0000

Dear CF-metadata list members,

having just signed up to the mailing list, I should probably "waist" a few words on a brief introduction. I'm managing the WMO Global Atmosphere Watch (GAW) World Data Centre for Aerosol (WDCA) at NILU. WDCA collects data on atmospheric aerosol properties measured at ground stations connected to the GAW network. One primary use of the data is for validating climate and weather prediction models, the latter to the degree they include aerosol explicitly. WMO is currently working towards a better integration of its several GAW data centres, as well as the aerosol observation and modelling communities in general. In this context, the need came up for a common, well-defined vocabulary for variables, for which we are considering the CF names. I'm not the only one to decide this, but if this is approved by the relevant WMO bodies, I will likely come to propose a few new standard names that correspond to aerosol properties observed at the GAW ground stations.

At this point however, I'm still trying to find out what these names will probably look like. To this end, I would have a few questions concerning the CF naming philosophy which I couldn't properly clarify by looking at the mailing list archives:

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?

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?

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"?

Thanks for your help!

Best regards,
Markus

_______________________________________
Dr. Markus Fiebig

Dept. Atmospheric and Climate Research (ATMOS)
Norwegian Institute for Air Research (NILU)
P.O. Box 100
N-2027 Kjeller
Norway

Tel.: +47 6389-8235
Fax : +47 6389-8050
e-mail: Markus.Fiebig at nilu.no
skype: markus.fiebig
Received on Tue Sep 06 2011 - 07:07:48 BST