Merenkorkeus

Merenkorkeus is the height of the sea surface used as a reference level for measuring the height of land and structures. It corresponds to mean sea level at a given location and serves as a vertical datum in surveying, navigation and hydrology. In practice, merenkorkeus provides the baseline from which elevations on land are measured.

The sea surface is not constant. It fluctuates due to tides, waves, wind, and atmospheric pressure. To define merenkorkeus, a long-term average of the sea surface is used, typically derived from tide gauge observations. The mean sea level is commonly estimated by averaging sea level over many years (often around the 18–19 year tidal cycle) to reduce the influence of tides and shorter-term variations.

In geodesy, merenkorkeus connects land elevations to the geoid, an equipotential surface that approximates mean sea level across the Earth. Elevation measurements from GNSS provide ellipsoidal heights, which must be corrected with geoid models to obtain heights above mean sea level. Consequently, the relationship between ellipsoidal height and merenkorkeus is defined by regional geoid models and height datums.

Changes in merenkorkeus over time reflect both global sea-level rise and regional vertical movements such as land uplift or subsidence. National height systems are periodically updated to account for these changes and to maintain accurate vertical references for mapping, construction and flood management.

Applications of merenkorkeus include civil engineering, harbor and infrastructure planning, flood risk assessment, cartography, and environmental monitoring.