# How Does Doppler Radar Work?

One discovery that is used in a variety of ways is the Doppler effect, even though at first glance the scientific discovery would seem to be rather impractical.

The Doppler effect is all about waves, the things that produce those waves (sources), and the things that receive those waves (observers). It basically says that if the source and observer are moving relative to each other, then the frequency of the wave will be different for the two of them. This means that it's a form of scientific relativity.

There are actually two main areas where this idea has been leveraged into a practical outcome, and both have ended up with the handle of "Doppler radar." Technically, Doppler radar is what is used by police officer "radar guns" to determine the speed of a motor vehicle. Another form is the Pulse-Doppler radar which is used to track the speed of weather precipitation, and usually, people know the term from it being used in this context during weather reports.

Doppler radar works by sending a beam of electromagnetic radiation waves, tuned to a precise frequency, at a moving object. (You can use Doppler radar on a stationary object, of course, but it's fairly uninteresting unless the target is moving.)

When the electromagnetic radiation wave hits the moving object, it "bounces" back toward the source, which also contains a receiver as well as the original transmitter. However, since the wave reflected off of the moving object, the wave is shifted as outlined by the relativistic Doppler effect.

Basically, the wave that is coming back toward the radar gun is treated as an entirely new wave, as if it were emitted by the target it bounced off of. The target is basically acting as a new source for this new wave. When it is received at the gun, this wave has a frequency different from the frequency when it was originally sent toward the target.

Since the electromagnetic radiation was at a precise frequency when sent out and is at a new frequency upon its return, this can be used to calculate the velocity, v, of the target.