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What is "Sea Level"?
What is "Sea Level" as used in describing the height of a mountain?
What is "Sea Level" as used in describing the height of a mountain?
Originally posted by nautica
Sea level is just what it says. It has arbritrairily been defined as zero, which is the level of the sea.
Nautica
Ok, so you are standing on top of Everest, how do you know how far above sealevel it is? How do you know how far the sea is above sealevel, anyway?Originally posted by LURCH
It's averaged out for tides.
Originally posted by Monique
Ok, so you are standing on top of Everest, how do you know how far above sealevel it is? How do you know how far the sea is above sealevel, anyway?
For instance the Mediteranian sea, it is in connection with the Atlantic ocean through a small opening: the Street of Gibraltar.. does it mean that the Mediteranian sea is always at sealevel? (minimal effect of tides?)
But then I observed that Lake Erie in the US seemed to even have tides..
Yeah, so I went to the beach today (I did).. say I wanted to measure how much the water was above set sealevel, or below, because of tides.. how would I do that? I mean.. what is the reference??Originally posted by nautica
Sea Level is set to zero. It does not matter what tides do, the sea level measure does not change. I am sure if you wanted to take the time to do the calculations you could find the height of the tides due to the moon and the sun at any given time and find the exact hight of the sea. Or you could just use a gps and find it out.
Nautica
Originally posted by Monique
Yeah, so I went to the beach today (I did).. say I wanted to measure how much the water was above set sealevel, or below, because of tides.. how would I do that? I mean.. what is the reference??
Well, that makes sense :)Originally posted by LURCH
That's what I mean by "averaged"; find however high the water gets at high tide, and however low it gets at low tide, determine the average between these two, and that is Mean Sea Level.
No, sea level is a local thing and you build your 3d model based on local sea levels.Originally posted by Monique
Well, I really don't get it how can you measure that the water along the coast of Holland is of the same level, as the water along the coast of Australia.. halfway around the world?
Is there somewhere on the world a beacon which says: this is sealevel? Like there is the Greenwhich timezone, which says: this is t0?
Originally posted by Bystander
http://www.gmat.unsw.edu.au/final_year_thesis/p_epstein/monitr_t.htm [Broken]
Yes, we do have solar tides. Really, gravitational interaction of any two bodies creates tidal forces in both.HERE is a decent site on ocean tides.Originally posted by Monique
How about solar influences? If there were no moon, would we have solar tides? Theoretically how large could those be? How large are lunar tides anyway?
Yes, the position of the moon has a significant effect on the tides. To get a really good sea level average you need a pretty long time period (a year or so).So how complicated would they have made the calibrations? Say for Holland and Australia.. would the position of the moon be significantly different averaged for the same few days at the same locations?
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?
Standard commercial GPS is less accurate for the vertical axis, but its gotten a ton better with DGPS & WAAS.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
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 scenarioAndre 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]