Which instrument provides altitude above the terrain by measuring the round-trip radio signal to the ground?

Which instrument provides altitude above the terrain by measuring the round-trip radio signal to the ground?

• A. Barometric altimeter
• B. Radar altimeter
• C. GPS altitude
• D. Indicated airspeed

Answer: (B)

Radar altitude is the height above the terrain, determined by the round-trip time of a downward radio pulse. It works by sending a microwave signal toward the ground, receiving the echo, and computing distance to the surface using the speed of light. This gives the altitude above the ground, which is different from altitude above mean sea level or ellipsoid measurements. Barometric altimeters rely on ambient air pressure and don’t measure distance to the terrain. GPS altitude comes from satellite geometry and can have vertical errors. Indicated airspeed is a measure of speed through the air, not height.

Radar altitude is the height above the terrain, determined by the round-trip time of a downward radio pulse. It works by sending a microwave signal toward the ground, receiving the echo, and computing distance to the surface using the speed of light. This gives the altitude above the ground, which is different from altitude above mean sea level or ellipsoid measurements.

Barometric altimeters rely on ambient air pressure and don’t measure distance to the terrain. GPS altitude comes from satellite geometry and can have vertical errors. Indicated airspeed is a measure of speed through the air, not height.