[CF-metadata] fixed sensors, depth, datum

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 29 Sep 2008 11:33:03 +0100

Dear Jon

> - Being pedantic, two points at the same height above the geoid might
> not have quite the same potential energy. The 3D geopotential
> contours are not everywhere equally-spaced. However, I imagine this
> is not usually a large effect, unless the data in question are close
> to a large gravity anomaly.

If I understand you, then I agree. That is because geopotential is not the
same as gravitational potential, so height above a gravitational equipotential
surface is not the same as height above geoid. These again are two distinct
physical quantities.

> - Vertical coordinate values (heights, altitudes etc) are often
> inferred from other quantities (esp. pressure in both air and water).
> Since CF is expanding to include in situ data, can we express this
> somehow, so that users know that the coordinate value depends on
> certain assumptions?

Yes, we could, but I would not make that distinction in the standard name, if
the intention is just to supply some extra information about how the quantity
was obtained. That does not make different kinds of quantity. On the other
hand, if the quantities are regarded as distinct, so that you might have
several of them in the same dataset, and wanted to compare them with the
corresponding ones in another dataset, perhaps an argument could be made
for distinguishing them by standard name. However, another attribute might
still be a better way, I suspect. We would need some use-cases to discuss
this when it arises.

Cheers

Jonathan
Received on Mon Sep 29 2008 - 04:33:03 BST