Mike T. Mcclure, age 7, of Houston, TEX., for his question:
How does radar work?
Radar is related to radio. It carries messages at the speed of light, and nothing can travel faster than light. There are radar sets of all sizes for doing different jobs. Traffic officers use a small radar set to track speeding drivers. Airports use huge radar sets to scan the skies for planes hundreds of miles away.
When you shout at a cliff, you hear an echo. The sound of your voice travels on until it gets to the steep wall of rock. There it bounces and comes back to your ears. Radar works somewhat like an echo. But it does not use ordinary sound to bounce off an object. Instead it uses radio waves like those that bring programs from the station to a radio set.
Ordinary sound creeps along at about one fifth of a mile in a second. In that same second, a beam of radio waves travels 186,000 miles. If it could bend, a radio beam would whip around the equator seven times in a single second. But it must travel in a straight line.
In a radar set, a beam of strong radio waves is generated by a transmitter. A short pulse of radio energy goes from the transmitter to the radar antenna. The radio beam is sent straight out from the antenna to the target and returns to the antenna,. The target may be a high flying plane hundreds of miles away. It may be an iceberg half a mile from a fog bound ship. It may be a distant storm cloud. The radio beam travels to the target and bounces back to the radar set in a tiny, tiny fraction of a second. The echo from the target is faint, so it goes to an amplifier which makes it stronger. The stronger radar echo goes to the indicator, Which is a cathode ray tube like a TV screen. When the Echo has been shown in the Radar screen, another burst of radio energy is sent out. The radio beam goes out and its echo returns again and again in every second. The ethos make bright blips on the Radar screen.
Radar is shorthand for radio detection and ranging. A timer in the set tel1s how long it takes each beam to reach the target and return. Since we know the speed of radio, this gives the distance of the target. The antenna turns its head to scan the surroundings. The blips on the screen show the direction of the target. Radio beams pass through fog and darkness. Ships and airports use their radar to point out obstacles at night and in foggy, cloudy weather. A big plane may use Radar to tell how high it is from the ground. The weathermen use radar to spot a distant storm. Radar beams are used to tell the distance of the moon and the height of mountains. Even bird watchers use it to spot migrating birds.