Doppler Effect:

• It gives the relation between frequency of signal and position of observer which is moving.

• The speed of source and the receiver relative to the medium are lower than the velocity to the waves in the medium, the relationship between observed ‘f’ and emitted frequency $f_0$ is given by

  $f=\bigg[\dfrac{C+V_r}{C+V_s}\bigg] f_0$

  C = Velocity of light in medium

  $V_r$ = Velocity of receiver relative to the medium and is positive if the recever is moving towards source.

  $V_s$ = Velocity of source relative to the medium and is positive if the source is moving away from the receiver.

• The frequency is decrease if either is moving away from the other.

• The relation b etween the observed frequency if emitted frequency f0 is given by

  $f=\bigg(1-\dfrac{V}{C}\bigg) f_0$

  Change in frequency

  $∆f=\dfrac{V}{C} f_0=f-f_0$

  V = velocity of source relative to receiver it is positive when the source and receiver are moving further apart.

  C = Speed of light.

Funcxtioning of some types of radar are based on Doppler effect to measure the velocity of detected object. - CW Doppler Radar - CW MTI Radar

CW Doppler Radar:

• CW radar transmits unmodulated CW energy. Here the energy reflected by a moving target gets shifted in frequency by factor∆f.
• The difference frequency∆f is indication of the presence of the moving target and gives its redial velocity $V_r$.