radio altimeter

A radio altimeter is an instrument used to measure the absolute altitude of an aircraft, meaning its distance above the ground or water directly below. It operates by emitting radio waves and measuring the time it takes for these waves to travel to the ground and reflect back to the aircraft. This time lag is then converted into a precise altitude reading, which is often displayed on a video screen.123

Radio altimeters are crucial for modern aviation, particularly in automatic navigation and blind-landing systems, helping pilots maintain a safe descent rate before touchdown. Unlike pressure altimeters, which measure altitude above sea level based on atmospheric pressure, radio altimeters provide a direct measurement of height above the terrain.13