In the actual video he seems to have misunderstood what the Doppler effect actually is. He gives the example of a train whistle "getting louder as it comes towards you and fainter as it moves away" but he should have said something along the lines of "the same way that a train whistle has a higher pitch as it moves towards you and a lower pitch as it moves away from you". The intensity of the signal is much harder to measure/calibrate than the frequency of the signal.