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
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--
Ethan R. Davis Telephone: (303) 497-8155
Software Engineer Fax: (303) 497-8690
UCAR Unidata Program Center E-mail: edavis at ucar.edu
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Received on Fri Sep 26 2008 - 12:43:02 BST
