The Doppler effect refers to the phenomenon that when the wave source and the observer make relative movements, the frequency received by the observer and the frequency emitted by the wave source is different. When the two are close to each other, the received frequency increases and decreases when they leave each other. According to the above definition, Which of the following do not use the Doppler effect:. ['Doppler navigation.', 'Laser velocimeter.', 'Color Doppler.', 'Doppler camera.']