The variation in the frequency of a wave for an observer moving relative to the source of the wave is called Doppler effect. A decrease in the wavelength and increase in the frequency of the wave is called as a Blue shift and it is caused due to the movement of source towards the observer. This web page shows the Doppler effect blue shift velocity formula which helps you to calculate the velocity by multiplying the C (speed) with divided value of E (emitted wavelength) and B (blue shift wavelength) reduced by 1.