A radar altimeter determines altitude by

A radar altimeter determines altitude by

• A. Radio signal from bottom of aircraft bouncing off the ground
• B. Thermal radiation emitted by the aircraft surface
• C. GPS triangulation
• D. Barometric pressure derived altitude

Answer: (D)

Radar altimeters measure height above the ground by sending a downward-directed radio pulse from the underside of the aircraft, waiting for the echo to return from the ground, and calculating the distance from the round-trip travel time. Since radio waves travel at the speed of light, the altitude above the surface is obtained from half the round-trip time multiplied by that speed. This gives precise height above ground (AGL), which is why radar altimeters are especially useful during approach and landing. This method is different from barometric altitude, which uses changes in air pressure to estimate altitude relative to sea level, and from GPS-based height, which derives position and height from satellite signals and can be less precise near the ground. Thermal radiation is not used to determine altitude.

Radar altimeters measure height above the ground by sending a downward-directed radio pulse from the underside of the aircraft, waiting for the echo to return from the ground, and calculating the distance from the round-trip travel time. Since radio waves travel at the speed of light, the altitude above the surface is obtained from half the round-trip time multiplied by that speed. This gives precise height above ground (AGL), which is why radar altimeters are especially useful during approach and landing.

This method is different from barometric altitude, which uses changes in air pressure to estimate altitude relative to sea level, and from GPS-based height, which derives position and height from satellite signals and can be less precise near the ground. Thermal radiation is not used to determine altitude.