sea level measurements
From Glossary of Meteorology
Averaging out the effects of waves to determine sea level.
The measurements can be made in several ways, for example, for the reading of tide poles, the averaging is by eye, in stilling wells the waves are damped out by a narrow constriction, acoustic and pressure gauges may apply electronic averaging to rapid samples, and satellite altimetry is corrected for general wave conditions within the footprint of the transmission.
