What is mean sea level ?

The average height of the ocean's surface over a long period (typically 19 years), used as a reference point or datum for measuring elevations and depths.

Mean Sea Level (MSL) is a crucial reference datum in various scientific and engineering fields. It represents the average height of the sea surface for all stages of the tide over a long period of time, usually 19 years, at a particular location. This long averaging period helps to filter out short-term fluctuations caused by tides, waves, storms, and other meteorological and oceanographic phenomena.

Key aspects and applications of MSL include:

    
• Datum for Elevation: MSL serves as the fundamental zero-level for measuring land elevations and depths in oceans and seas. All elevations on maps and charts are typically referenced to MSL.
    
• Geodesy and Mapping: It is critical for geodetic surveys, cartography, and establishing consistent vertical reference systems across regions and continents.
    
• Oceanography and Climate Change: Oceanographers use MSL to study ocean currents, tidal patterns, and changes in sea level over time, which are vital indicators for understanding climate change and its impacts.
    
• Engineering and Construction: Engineers use MSL as a benchmark for designing and constructing coastal infrastructure, bridges, ports, and flood defenses.
    
• Navigation: Mariners rely on charts referenced to MSL for safe navigation, understanding water depths, and planning routes.

Factors influencing the actual instantaneous sea level include gravitational forces (tides), atmospheric pressure, wind, ocean currents, temperature, and salinity. By averaging over an extended period, MSL provides a stable and reliable baseline for these measurements.