resending to the list...
Heiko,
If I understand correctly, then the height above mean sea level can be encoded
as either the altitude, which is above the particular reference frame called
the geoid [1], or height_above_reference_ellipsoid, which allows specification
of a particular reference frame (which could be the geoid, but then you would
likely use altitude instead, for simplicity). Since the geoid is so close to
the mean sea level, using altitude makes sense for grib's #2, unless you know
of a reason some other reference ellipsoid should be specified.
I don't know grib so I don't know how they define terms like 'geometric height'
[2], but again using the dumb Wikipedia approach ("Elevation, orgeometric
height, is mainly used when referring to points on the Earth's surface, while
altitude or geopotential height is used for points above the surface"), it
seems surface_altitude could be the right choice for grib's #4.
John
[1] Wikipedia's language is nice: "The geoid is the shape that the surface of
the oceans would take under the influence of Earth's gravitation and rotation
alone, in the absence of other influences such as winds and tides."
[2] Found http://www.wmo.int/pages/prog/www/WDM/Guides/Guide-binary-2.html, but
no clarification of the term 'geometric height' was given there. Are there
other references?
On Feb 7, 2014, at 03:52, Heiko Klein <[email protected]> wrote:
> Hi,
>
> the CF documentation has several standard_names for dimensionless vertical
> axes, while standard_names for vertical axes with units are mentioned, but
> not given.
>
> grib has for metric vertical axes the following descriptions:
>
> 1. height above ground
> 2. height above mean sea level
> 3. depth below surface
> 4. geometrical height
>
>
> Matching standard names are eventually
>
> 1. height
> 2. height_above_reference_ellipsoid / altitude ? (are these two aliases?)
> 3. depth
> 4. ?
>
>
> I'm currently fighting with 2. Which one is correct? Which one should be used
> for vertical axes?
>
> And for pressure vertical coordinates: is the correct standard_name
> 'air_pressure'?
>
> Could these eventually be mentioned in the Convention besides the
> standard_names for dimensionless vertical coordinates?
>
>
> Best regards,
>
> Heiko
>
> --
> Dr. Heiko Klein Tel. + 47 22 96 32 58
> Development Section / IT Department Fax. + 47 22 69 63 55
> Norwegian Meteorological Institute http://www.met.no
> P.O. Box 43 Blindern 0313 Oslo NORWAY
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