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[CF-metadata] fixed sensors, depth, datum

From: Ethan Davis <edavis>
Date: Fri, 26 Sep 2008 12:43:02 -0600

Hi Jonathan,

I would argue against them being different quantities because there
exist transformations between these various heights. Is that not enough
to indicate they are the same quantity?

Ethan

Jonathan Gregory wrote:
> Dear Jon
>
>
>>> - height relative to the ellipsoid
>>> - height relative to the geoid
>>>
>> From a coordinate referencing point of view they both
>> give height (in units of length) above a reference surface, but the
>> surfaces happen to be different. Do you consider them geophysically
>> distinct because "height relative to geoid" is a close approximation
>> to potential energy, whereas "height relative to ellipsoid" is not?
>> Similarly, the geoid approximates sea level whereas the ellipsoid does not?
>>
>
> Yes, I would say that distinctions like that make them different quantities.
> Plain "height" (above the surface) is likewise a different geophysical
> quantity. However, I think that specification of geoid or ellipsoid is not part
> of the identity of the geophysical quantity. It is more in the nature of an
> extra parameter for working out the numbers, like the reference pressure used
> for potential temperature. Of course, I realise this is somewhat arbitrary.
>
> Best wishes
>
> Jonathan
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>

-- 
Ethan R. Davis                                Telephone: (303) 497-8155
Software Engineer                             Fax:       (303) 497-8690
UCAR Unidata Program Center                   E-mail:    edavis at ucar.edu
P.O. Box 3000
Boulder, CO  80307-3000                       http://www.unidata.ucar.edu/
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Received on Fri Sep 26 2008 - 12:43:02 BST

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