Can anyone tell me how Sea level is calculated ?
As in so many feet above or below “Sea Level”.
Also, is this an international standard? As I would assume that with the gravitational effect the moon has on our tides, and the centrifugal effect of the planet spinning, most areas of the oceans actual surface would deviate or – to some degree from the recognized mean, some quite considerably!
Thanks in advance
Daryl
“sea level” as used in elevation mapping (topography) is actually more precisely called “Mean Sea Level”. originally this value was established for a given location and thus is not really a good standard because the value will differ from place to place. I think originally the maps were standardized using a MSL value from a chosen location. Over time, increasing precision and better understanding of the gravity geoid (a representation of the earth surface where the gravity is identical, it is not a sphere but varies somewhat) led to the development of different models, or standards. It can get a bit complicated, as standardized mean sea level can differ from the geoid.
See this reference for a decent discussion (applicable for canada):
http://www.geod.nrcan.gc.ca/hm/msl_e.php
There are different standards for the x-y coordinates too (or datums such as WGS84, NAD27, NAD83, and so on). All modern topographical maps will tell you which of these is the basis of the map. Different standards will provide you with different elevations and x-y coordinates, so if you are working with this stuff, you need to be sure to use the same datum for all of your measurements and calculations.
Sea Trout in Rivers – Spin fishing