What is Sea Level ?

  • #26
Michael D. Sewell
Monique said:
Is there somewhere on the world a beacon which says: this is sealevel? Like there is the Greenwhich timezone, which says: this is t0?
Yes, as a matter of fact, there is. Check with a local surveyor. He or she can tell you where to find a datum point or bench mark.

As mentioned before, GPS is not accurate enough to measure height.

Also, Don't forget about atmospheric tides when using your barometer.

-Mike
 
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  • #27
4,465
72
Yes how about a sea level change of 750 meters?

http://www.cuba.cu/ciencia/citma/ama/museo/exmari.htm [Broken]
(not an attempt to steal the thread) :wink:

Monique,

some usefull links for Dutch sea level history:

http://www.ncg.knaw.nl/SubBZ/BeginSubBZ.htm [Broken]
http://hanserren.cwhoutwijk.nl/co2/denhelder.html [Broken]

the webpage of an acquintance who has an interesting hobby.

Bottom line is that we have no good idea about what's happening and there is no need for alarm. So this is not the reason why I changed my -1,5 meter elevation residence in Holland for an appartment at +975 meters in Germany :wink: (Still a lot of snow here)
 
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  • #28
Nereid
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Both GRACE and GOCE (the Gravity Field and Steady-State Ocean Circulation Mission) will improve understanding of the geoid (to +/- 1cm) and ocean circulation.
 
  • #29
russ_watters
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ray b said:
GPS is NOT accurate enuff for hight data as it has the biggest error rate
about 10x the error rate of the x+y location data for the z hight axis
Standard commercial GPS is less accurate for the vertical axis, but its gotten a ton better with DGPS & WAAS.

Surveyors use equipment optomized for stationary measurments though - and its a good order of magnitude more accurate than typical systems.

edit: HERE is a good site listing several types of systems and their accuracies. For surveyors its 1-30cm in 2d and 1.6 to 45cm 3d.
 
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  • #30
Michael D. Sewell
On the ball

Russ,
The last I knew, the best GPS systems were only accurate to within 1 meter.
Thanks for the update, and thanks for the link.
-Mike
 
  • #31
4,465
72
Amazing GRACE

Nereid

Amazing GRACE :wink: and GOZE and breath taking results:

GOCE_S_C2_geoid_bg_L.jpg


Notice that the deep red areas are more or less -very roughly- antipode. That reminds me of another World map in relation to sea levels:

http://home.wanadoo.nl/bijkerk/palaeogeography.GIF [Broken]

With a little imagination you could draw an oblique geographic world from that, the poles being in the centre of the blue spots, the equator following the big orange wave. Aint it curious?

This is the origine of that second pic: http://www.sciencemag.org/cgi/content/full/295/5564/2438
 
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  • #32
Monique
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Andre said:
some usefull links for Dutch sea level history:

http://www.ncg.knaw.nl/SubBZ/BeginSubBZ.htm [Broken]
http://hanserren.cwhoutwijk.nl/co2/denhelder.html [Broken]
That second link is very interesting. Actually I just remember now.. a few weeks ago there was a very stormy western wind. I was at the west of the IJsselmeer (a lake) and the water level was SO low! that you could actually go down and walk on the bottom of the lake for a considerable length from the bank.. reminded me of that tale where the water parted and Jesus walked across a lake.. sounds very possible in such a scenario :biggrin:
 
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