Re: [cf-pointobsconvention] Should Z Coordinates be required?

It occurs to me that we could document the possible vertical coordinates, ie set up a controlled vocabulary. The WMO has already done so in the GRIB2 format:

 http://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_table3-15.shtml
 http://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_table4-5.shtml

or we could refer to these if deemed complete enough.

This could be an appendix that might would be useful to storing any type of 
data in CF.


Jonathan Gregory wrote:
Dear John G

Also I don't think we should confuse the z of the quantity being measured with 
the z
of the platform which is measuring it.
I don't think we are confusing those two values.

For a precipitation flux or a pressure at mean sea level (calculated by
correcting surface pressure to sea level) there a station altitude, of course,
but that is not the "altitude" of the quantity measured. Precipitation is by
definition a surface quantity, and pressure at mean sea level is at mean sea
level, so doesn't have an altitude. I would regard the altitude in these cases
as useful ancillary metadata, but not a coordinate. For temperature measured in
a met enclosure, the Z coordinate would be height (=1.5 m or 2 m). The
station still has the same altitude as for the precipitation measurement, but
you would record the height, not the altitude, as the Z coord. (At least, in
all the model data archived at PCMDI, surface air temperature has a Z coord
of height.) I think that shows that the altitude of the station is *not* the Z
of the precipitation or the sea-level pressure value. However, it is definitely
useful to know and should be recorded.

Best wishes

Jonathan G
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