How does a radar altimeter determine altitude?

A radar altimeter determines altitude by transmitting a signal toward the ground and then measuring the time it takes for that signal to be reflected back to the aircraft. This process relies on the principles of radar technology. The radar altimeter sends out a pulse of microwave energy, which travels to the terrain below and bounces back to the aircraft. By calculating the time interval between the transmission of the signal and the reception of the reflected signal, the altimeter can determine the distance to the ground, which is then used to calculate the altitude of the aircraft above the terrain.

This method is particularly useful at low altitudes, as it provides a precise measurement above the surface, independent of atmospheric conditions that can affect other forms of altitude measurement, such as barometric altimeters.