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Sea level measurements

Introduction

Sea level changes on a variety of space- and time-scales, and different measuring systems measure different subsets of the various components that make up the total picture. This is further complicated by the fact that different observing systems measure sea level in different reference frames, and that geological effects (long- and short-term) can move the reference frame and/or the sea level with respect to that reference frame! See our section "Why does sea level change" for more information on this.

The following table summarizes some of these issues:

	Time scale	Spatial scale	Reference frame	Other problems
Paleo indicators	decades to tens-of-thousands of years	localised coastal and islands scattered in time and space	land to which they are attached which can be moving vertically because of large- or small-scale geological effects	large errors, some types only happen in one type of environment (e.g. where land is rising)
Tide gauges	minutes to centuries (includes "weather", and tides)	localised coastal and islands small number of good quality records	land/structure to which they are attached which can be moving vertically because of large- or small-scale geological effects	difficulty of tying together different instrumentation at one site to give a long, consistent time series
Satellite altimeters	20 days to 15 years	global, but miss some coastal phenomena	referenced to the centre of mass of the Earth (via a reference surface such as a reference ellipsoid). One effect of this is that, as the shape of the ocean basins is changing slowly with time, a correction needs to be made to the altimeter data for this.	insufficient temporal sampling for some purposes

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Website owner: Benoit Legresy | Last modified 22/04/08

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