[CF-metadata] fixed sensors, depth, datum

From: Jonathan Gregory <j.m.gregory>
Date: Fri, 3 Oct 2008 17:14:09 +0100

Dear Ethan

Ah good - I am glad we agree now about the geophysical distinction. I agree
with this too:

> It seems there are two important characteristics that need capturing:
> 1) the geophysical significance of a vertical CRS (height, altitude,
> pressure, sigma, etc), and
> 2) the details of a vertical CRS, possibly enough to enable
> intercomparison with data on a different vertical CRS.
>
> The first seems appropriate to capture in the standard name attribute.

I too am unsure about how station vertical datums should be dealt with, because
I remain in the dark about what they mean. I suspect (as I've said before)
that it may mean that a given physical location (a benchmark) is assigned a
particular height above a specified definition of the geoid, and hence fixes
the altitude of all other locations - but I would be very grateful to be
corrected or enlightened.

I think that the tidal datums, which Dale raised when he started this thread,
are distinct geophysical quantities. They again are things which have to be
measured and distinguished and might coexist in one dataset. There are several
of them, as you say, but not as many as there are of chemical species, for
instance, so I don't think they pose a serious problem.

You have pointed out before that the definition of the ellipsoid affects the
definition of lat and lon. Hence it relates to both vertical and horizontal
CRS. To avoid repetition, it seems to me that it would be better to keep them
in the same place. I agree with Phil that we could rename the grid_mapping
attribute e.g. to crs (keeping the old name as an alternative for existing
datasets). However, I understand that you don't like repeating the horizontal
CRS if you combine it with several vertical ones in the same dataset. When you
do this, what differs among the vertical CRSs?

Best wishes

Jonathan
Received on Fri Oct 03 2008 - 10:14:09 BST