Speed Gun

A speed gun, also radar gun, is a device used to detect the speed of moving objects, including vehicles, pitched baseballs, runners and other moving objects. Speed guns consist of a radio transmitter and receiver. They send out a radio signal, then receive the same signal back after it bounces off the target object. Due to a phenomenon called the Doppler effect, if the object is moving, the frequency of the reflected radio waves when they come back is different from the transmitted waves, and from that difference the radar speed gun can calculate the object's speed.

Older speed guns use radar as radio signal, however more modern LIDAR speed guns use pulsed laser light instead of radar and are more commonly used now. LIDAR speed guns work by sending out a stream of approximately 100 pulses over the span of three-tenths of a second. The reflected signals are then processed using statistical algorithm to pick which reflected signals to retain. The new speed gun allows a police officer to measure the speed of an individual vehicle within a stream of traffic. They are frequently used for speed limit enforcement.

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