Height above mean sea level Facts for Kids

"AMSL" redirects here. For the Canadian soccer league, see Alberta Major Soccer League. For the Airbus company, see Airbus Military.

Height above mean sea level (often called AMSL) is a way to measure how high something is. It tells us the vertical distance of a place, like a mountain or a town, compared to the average level of the ocean. Think of it like a giant ruler that starts at the sea's surface.

This measurement is usually given in metres (like "metres above mean sea level"). In some places, like the United States, it might be given in feet ("feet above mean sea level").

The average sea level can change over time. This happens because of things like climate change or natural movements of the Earth's land. So, a measurement taken many years ago might be slightly different from today's actual height.

Why We Measure Height Above Sea Level
How We Measure Height Above Sea Level
Common Abbreviations
See also

Why We Measure Height Above Sea Level

Measuring height above sea level is super important for many reasons. It's used all over the world to understand how high things are.

Measuring Geographic Places

It helps us know the elevation of Geographic locations. This includes cities, towns, and famous landmarks like mountains. For example, we know Mount Everest is the world's highest peak because its height above mean sea level has been carefully measured.

Measuring Buildings and Structures

We also use it to measure the height of tall buildings and other big structures. This helps engineers and builders plan their projects.

Measuring Flying Objects

For things that fly, like airplanes or helicopters, height above sea level is crucial. Pilots use this measurement to know how high they are flying. This is especially important in countries like China and Russia, and many other nations that were once part of the CIS.

How We Measure Height Above Sea Level

There are several clever ways to figure out how high something is above sea level. Each method has its own uses and tools.

Using Satellites (GPS)

One common way is using a Global Navigation Satellite System (like GPS). A special receiver on the ground talks to many satellites orbiting Earth. By measuring the time it takes for signals to travel, the receiver can figure out its exact spot. Then, it uses a special map of Earth's gravity (called a geoid) to convert that 3D position into a height above sea level.

Using Altimeters (Air Pressure)

An Altimeter is a device that measures atmospheric pressure. Air pressure naturally gets lower as you go higher up. So, an altimeter can tell you your altitude based on how much air is pressing down on it. However, weather can also change air pressure, so altimeters need to be regularly checked against a known pressure at a certain height.

Using Aerial Photography

Stereoscopy in aerial photography involves taking pictures from an airplane. By looking at two photos of the same area from slightly different angles, experts can create a 3D view. This 3D view helps them measure heights accurately.

Using Lasers (Lidar)

Aerial lidar and satellite laser altimetry use lasers. A laser sends out light pulses and measures how long it takes for them to bounce back from the ground. This time difference helps calculate the distance, and thus the height.

Using Radar

Aerial or satellite radar altimetry works similarly to lidar but uses radio waves instead of lasers. Radar sends out radio signals and measures the time it takes for them to return, helping to determine height.

Using Surveying Tools

Surveying, especially a method called levelling, is a very precise way to measure height. Surveyors use special tools to measure small differences in height between points on the ground, slowly building up a picture of the landscape's elevation.

It's tricky to measure the exact average sea level from a long time ago. Sometimes, land itself can sink (called subsidence) or rise due to natural geological processes. This can make it seem like the sea level is changing more than it actually is.

Common Abbreviations

You'll often see "height above mean sea level" shortened.

Sometimes, just the abbreviation MSL is used. For example, you might see "Mount Everest (8848 m MSL)".
Even simpler, the reference height might be left out completely, like "Mount Everest (8848 m)".
"Metres above mean sea level" is commonly abbreviated as mamsl or MAMSL. This comes from the abbreviation AMSL for "above mean sea level".
Other abbreviations you might see are m.a.s.l. and MASL for "metres above sea level".

Height above mean sea level facts for kids

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