Mean Sea Level

Mean sea level (MSL) is the average height of the sea’s surface over a period of time, typically 19 years. It is a reference point for measuring elevations and changes in sea level.

MSL is determined by averaging hourly tide measurements over the period of time. This average is then adjusted for the effects of non-tidal factors, such as atmospheric pressure and wind.

There are two main methods for determining MSL:

Tide gauges:

Tide gauges are instruments that measure the height of the sea surface at a specific location. The data from tide gauges is used to calculate MSL at that location.

Satellite altimetry:

Satellite altimetry is a remote sensing technique that uses satellites to measure the height of the sea surface. Satellite altimetry data is used to calculate global MSL.

Tide gauges are more accurate than satellite altimetry, but they are also more expensive to install and maintain. Satellite altimetry is less accurate than tide gauges, but it provides global coverage.

MSL is an important measurement for a number of reasons. It is used to:

Measure changes in sea level:

MSL is used to measure changes in sea level over time. This information is used to study climate change and its effects on sea levels.

Map the seafloor:

MSL is used to map the seafloor by measuring the depth of the water relative to MSL.

Design coastal structures:

MSL is used to design coastal structures, such as seawalls and breakwaters, to protect coastal communities from flooding and erosion.

MSL is a dynamic measurement that is constantly changing. Sea levels are rising due to climate change, and this is causing MSL to rise as well. The rate of sea level rise is expected to accelerate in the coming decades.

Here are some examples of how MSL is used:

Climate change research:

Scientists use MSL measurements to study climate change and its effects on sea levels. For example, scientists have used MSL measurements to show that sea levels are rising at an accelerating rate.

Coastal engineering:

MSL is used by coastal engineers to design coastal structures, such as seawalls and breakwaters, to protect coastal communities from flooding and erosion. For example, MSL is used to determine the height of seawalls to protect coastal communities from storm surges.

Navigation:

MSL is used to create nautical charts, which are used by mariners to navigate the seas. Nautical charts show the depth of the water relative to MSL.

MSL is an important measurement for a variety of reasons. It is used to study climate change, design coastal structures, and create nautical charts.