Question

How is the velocity of an aircraft measured by passive radio systems?

(a) Doppler shift

(b) Velocity data is transmitted by the aircraft and received by the station

(c) Secondary surveillance method

(d) Satellite mapping

The question was posed to me in class test.

The doubt is from Guidance and Navigation in chapter Introduction & Navigation Equations of Avionics

Answer 1

Correct choice is (a) Doppler shift

For explanation: The aircraft’s velocity is measured from the Doppler shift of the transmission or from a sequence of position measurements. Since the aircraft is continuously moving, each interrogation pulse when it is received will have different phase shift which corresponds to the aircraft’s velocity.