Doppler effect velocimetry principle

The Doppler effect shows that when the wave source is close to the observer, the receiving frequency of the wave becomes higher, and when the wave source is far away from the observer, the receiving frequency becomes lower.

There is an interesting phenomenon in life: the ambulance is coming head-on, and the sound is louder than before; And the sound of the car is lower than before when it leaves. You may not realize that this phenomenon belongs to the same principle as the color Doppler ultrasound used in hospitals, that is, the "Doppler effect". The Doppler effect shows that when the wave source is close to the observer, the receiving frequency of the wave becomes higher, and when the wave source is far away from the observer, the receiving frequency becomes lower.

The displacement of the spectral line of the star shows the speed of the star moving along the observation direction. Unless the speed of the wave source is very close to the speed of light, the degree of Doppler shift is generally small. All fluctuations have Doppler effect.

Doppler effect:

The Doppler effect was named in memory of Austrian physicist and mathematician Christian John Doppler, who first proposed this theory in 1842. The main content is that the wavelength of the object radiation changes due to the relative motion between the wave source and the observer.

In front of the moving wave source, the wave is compressed, the wavelength becomes shorter and the frequency becomes higher (blue shift); When it is behind the moving wave source, it will have the opposite effect. The longer the wavelength, the lower the frequency (red shift); The higher the speed of the wave source, the greater the effect. According to the red (blue) shift degree of the wave, the speed of the wave source moving along the observation direction can be calculated.