DOPPLER EFFECT

It explains the change in frequency as sources and observers move towards each other/ away from each other. 

Source moving to/from observer

EX. RADAR GUNS

A radar speed gun measures the speed of the objects at which it is pointed at by detecting a change in frequency of the returned radar signal caused by the Doppler effect. The frequency of the returned signal is increased in proportion to the object's speed of approach if the object is approaching, and lowered if the object is receding

Radar speed guns consist of a radio transmitter and receiver. They sendout a radio signal in a narrow beam, then receive the same signal back after it bounces off the target object.

If the object is moving toward or away from the gun, the frequency of the reflected radio waves when they come back is different from thetransmitted waves.

From that difference, the radar speed gun can calculate the speed of the objectfrom which the waves have been bounced.This speed is given by the following equation:

Ex. Radial Velocity - The Wobble Method

• one of the first discovered and most productive ways to find exoplanets

• a planet orbiting a star exerts a (very small) gravitational pull on the star, causing it to 'wobble'
• when the exo-planet is in front of the star, the lines in the star's emission spectrum experience a Doppler blue shift    

Doppler Ultrasound

• similar to a radar gun, but Doppler Ultrasound tests use reflected sound waves to measure the speed of red blood cells through blood vessels using frequency shifts
• ultrasound is used in order to reduce diffraction (higher frequency and lower wavelength lead to less diffraction), which helps to produce clearer images
• this test can help doctors to detect blood clots, embolisms and to check the blood flow of unborn babies

Other Applications 

• in some cases pulses of radiation are sent out rather than beams of radiation
  • one application specific to pulse- doppler radars: the swirling depictions of weather patterns