What is required to accommodate for the ground effect in swiveling pitot tube below rotor system?

A)
Radio altimeter
B)
GPS
C)
Doppler
D)
Secondary radar

Correct Answer :   Radio altimeter


Explanation : The principle of the probe is that the horizontal component of the induced flow velocity is a repeatable function of horizontal airspeed but varies with ground proximity. Hence, a radar altimeter is required to accommodate the ground effect.