How does a radar altimeter determine altitude?

• A. By sending and receiving voice signals
• B. By measuring the aircraft's altitude through radio waves
• C. Using GPS for horizontal positioning
• D. By analyzing atmospheric pressure

Answer: (B)

A radar altimeter determines altitude by measuring the time it takes for radio waves to travel from the aircraft to the ground and back. This technology relies on the transmission of radar signals, which are emitted by the aircraft and bounce off the surface below. By calculating the time delay between sending the signal and receiving the echo, the altimeter can accurately determine the distance to the ground, which is then used to establish the altitude of the aircraft above the terrain.

This method is particularly effective for measuring low altitudes, making radar altimeters essential for approaches, landings, and flying over uneven terrain. The use of radio waves allows for real-time altitude measurements that are not influenced by the aircraft's speed or the outside atmospheric conditions, unlike other altitude measuring systems.

Other options provided do not accurately reflect how a radar altimeter works. For example, sending and receiving voice signals does not play a role in altitude measurement, and using GPS is more about determining geographical position rather than altitude alone. Atmospheric pressure is related to barometric altimetry, which measures altitude based on changes in air pressure rather than using radar technology.