[NatureNS] Determining Elevation

References: <45EEB94D.23068.2C7B1209@heather.drope.ns.sympatico.ca> <45EEF78F.8030503@zdoit.airpost.net>
From: Steve Shaw <srshaw@dal.ca>
Date: Wed, 7 Mar 2007 14:43:14 -0400
To: naturens@chebucto.ns.ca
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    Interesting original question from Paul, so I looked it up in (where 
else but?) Wikipedia -> sea level -> mean sea level (MSL), where 
there's a readable but somewhat technical explanation.   Conceptually, 
MSL is defined apparently by a 3-dimensional imaginary geometric 
surface hovering around the earth, a geoid, at which sea level would 
equilibrate if there were no variations in air pressure etc, but from 
which there are real departures of up to +/- 2 meters.   It also says 
that an ellipsoid surface is easier to model than a geoid in order to 
tie into the GPS system for aircraft navigation, for aviators who wish 
to land on aircraft carriers, etc, and is increasingly used.  Changes 
in MSL over geological time are also covered a bit.
    The article also mentions apparent changes in sea level caused by 
land sinking or rising locally, but you'd need to look elsewhere for 
specifics.   I also thought that NS overall was still rebounding slowly 
from the oppressive weight of the last ice age, but it would need a 
geologist to tell us whether such changes are bigger or smaller than 
the projected rise in overall sea level caused by such things as 
current and future melting of ice on land, and sea water warming.
Steve, Halifax

On 7-Mar-07, at 1:34 PM, Gerald Ruderman wrote:
> Heather Drope wrote:
> . . . .
>> I have heard  that the province is sinking and the oceans are 
>> raising. If
>> that is the case I wonder what they do then about their bench 
>> marks?Will
>> they be adjusted or is this something we don't have to worry about in 
>> my
>> generation.  Heather
>
> Sinking! I thought it was still springing back up after being pushed
> down during the ice age. I do agree about the oceans rising.
>

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