An apparent change in frequency of a wave due to the relative motion between a wave source and an observer.

What best describes a Doppler shift?

An apparent change in frequency of a wave due to the relative motion between a wave source and an observer.

What is the Doppler shift used for?

Doppler effect is used to measure speed in RADAR sensors. When the fixed-frequency radio wave sent from the sender continuously strikes an object that is moving towards or away from the sender, the frequency of the reflected radio wave will be changed. This frequency shift is known as Doppler effect, as shown in Fig.