I appreciate everyones's responses. I believe I have 2 of my 4 implied
questions answered sufficiently. That is, a standard_name for water level
which includes the concept of a non-geoid datum and an acceptable way to
define a vertical datum.
One of my remaining questions would be, where to put the datum
information. As an attribute? or as a several variable? If attribute,
what to call it? If variable, does it need a standard_name? (I don't
think an appropriate one exists) and how would the original variable (e.g.
water level) point to it (more of an issue if multiple datums are used
within the same file).
The final question was about the lack of a standard name for
depth referenced to a datum. Per the most recent response, I'll
go ahead an propose one and see what happens..
jrd
PS Regarding NGVD29/NAVD88 and Geoid. Not being a geodesist either,
I'll respond to that off list :)
On Wed, 13 Apr 2011, Jonathan Gregory wrote:
Dear Justin
Specifically, I'm trying to make sure that its clear that the "z"
(bathy/topo) and "eta" (water level) are being expressed relative to
either NGVD29 or NAVD88...currently the "CF Standard Names" for
"sea_surface_height*" mention only mean water level, geoid or
ellipsoid...none of which are really the same as NGVD29/NAVD88...and
the "depth" standard name has no other variants which look
appropriate.
Previous discussion on this topic include approaches of creating a
new standard names (e.g.
water_surface_height_above_reference_datum)
I think that is the correct approach for the standard name, and if you have
a need for it now, please propose such names. Of course, the above leaves the
the reference surface unspecified. I would argue that if the reference surface
has a geophysical meaning, it should be identified in the standard name e.g.
water_surface_height_above_mean_high_water
What sort of surface is NAVD88, if not an ellipsoid or a geoid? (Excuse my
ignorance - I am not a geodesist).
Best wishes
Jonathan
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