Radar

:This article is about the device. For the fictional character in M*A*S*H (movie) and M*A*S*H (TV series), see Corporal Walter (Radar) O'Reilly.

Speed measurement

Speed is the change in distance to an object with respect to time. Thus the existing system for measuring distance, combined with a little memory to see where the target last was, is enough to measure speed. At one time the memory consisted of a user making grease-pencil marks on the radar screen, and then calculating the speed using a slide rule.

Related Topics:
Speed - Distance - Time - Memory - Grease-pencil - Slide rule

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However there is another effect that can be used to make much more accurate speed measurements, and do so almost instantly (no memory required), known as the Doppler effect. Practically every modern radar uses this principle in the pulse-doppler radar system. It is also possible to make a radar without any pulsing, known as a continuous-wave radar (CW radar), by sending out a very pure signal of a known frequency. Return signals from targets are shifted away from this base frequency via the Doppler effect enabling the calculation of the speed of the object relative to the radar.

Related Topics:
Doppler effect - Pulse-doppler radar - Continuous-wave radar

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