Radar is actually an acronym that stands for Radio Detection And Ranging. It was developed in the early 1940s. Radar uses the echo principle. Radar equipment emits a high energy radio signal from an antenna. The signal travels out from the source until it is reflected back by contact with an object. The radar antenna relays this signal to a scope where the image is displayed. Using the time it takes for the emitted signal to reach the object and reflect back to its source, the distance to the object can be computed. The radar signal is moving at the speed of light and can make such a trip in microseconds.

In aviation, a ground radar antenna sends radio signal pulses into the sky. These signals are reflected back by aircraft flying in the airspace. The radar scope displays the direction and distance from which the signals are reflected back. This coupled with each aircraft's transponder signal identifies the aircraft on the radarscope. Also, all airliners are equipped with radar equipment in the aircraft's nose. Short bursts of radio signals are emitted from the nose cone of the aircraft. These signals reflect off clouds ahead of the aircraft. The on-board computer calculates the distance and displays the object (the cloud) on the on-board radar screen.