Pulse-doppler is a radar system that functions by sending short pulses of radio energy and simultanously listens for the echo from objects using the same attenna. The time delay between pulse transmission and echo reception gives the range to an object. Pulse-doppler radar uses the doppler shift principle to determine the relative velocity of objects. The Doppler effect is the change in frequency of any signal due to the finite speed at which the signal travels compared to the motion of the object. For instance, sound travels at the fairly slow speed of around 300 m/s, which is why you hear the Doppler effect of an ambulance siren as it passes you at 3 m/s or so. Although this results in a small 1% change in frequency, the human ear is very good at detecting this change.

In the case of radar the speed of light is much faster than sound and thus the resulting shift much smaller. However modern electronics are even better at detecting this change than the human ear is for sound. Speeds as slow as a few centimeters per second can be easily measured, an accuracy typically much better than for the measurement of distance.

The major use of pulse-doppler is to separate moving objects from clutter. It's common for doppler radars to have a frequency range adjust control to reject low speeds. Another form color-codes returns by their speed.

Doppler measures the speed only along the direction from the reflection to the radar antenna. In order to measure the object's true speed and direction, the radar set or operator had to remember a return's location. Military organizations traditionally used a manual plotting board for this purpose. Computers in the radar systems have made this even more convenient.