Positive and negative doppler shift

1. What is a positive Doppler shift?
2. What is negative Doppler shift?
3. What are the two cases of Doppler effect?

What is a positive Doppler shift?

As a convention, the velocity is positive if the source is moving away from us and negative if the source is moving towards the observer. Thus: if the source is moving away (positive velocity) the observed frequency is lower and the observed wavelength is greater (redshifted).

What is negative Doppler shift?

Notice that the Doppler shift is negative when the object is moving away (opening range) from the radar and is positive when the object is moving toward the radar (closing range).

What are the two cases of Doppler effect?

Different Cases of Doppler Effect. When we say source and observer are moving relative to each other, we get different cases as follows. Case I: An observer moving away from the stationary source. Case II: An observer moving towards the stationary source.