[eli5] How does an altimeter work? How does it know how high you are off the ground?

Question

[eli5] How does an altimeter work? How does it know how high you are off the ground?

In: 69

Answer 1

regular altimeter reads air pressure, and subtracts from it the air pressure at the ground level (which varies on weather). If you use this to land, somebody at the airport needs measure and tell you the air pressure there

radar altimeter indeed knows exactly how high you are, but only above a single spot on the ground directly below you. There is [at least one major plane crash](https://admiralcloudberg.medium.com/all-the-presidents-men-the-story-of-the-smolensk-air-disaster-and-the-death-of-lech-kaczyński-590a3977f) where pilots were misguided by a ravine right in front of the landing strip

finally, GPS-based systems such as [Terrain Avoidance](www.flyingmag.com/how-it-works-terrain-awareness-and-warning-system/) can tell you exactly where you are in all 3 dimensions. it also uses radar altimeter