Text 2 Uses of Radar

Radar is still most familiar as a military technology. Radar antennas mounted at airports or other ground stations can be used to detect approaching enemy airplanes or missiles, for example. The United States has a very elaborate Ballistic Missile Early Warning System (BMEWS) to detect incoming missiles, with three major radar detector stations in Clear in Alaska, Thule in Greenland, and Fylingdales Moor in England. However, it is not only the military men that use radar. Most civilian airplanes and larger boats and ships now have radar too as a general aid to navigation. Every major airport has a huge radar-scanning dish to help air traffic controllers guide planes in and out, whatever the weather. Next time you head for an airport, look out for the rotating radar dish mounted on or near the control tower.

You may have seen police officers using radar guns by the roadside to detect people who are driving too fast. These are based on a slightly different technology called Doppler radar. You have probably noticed that a fire engine's siren seems to drop in pitch as it screams past. As the engine drives toward you, the sound waves from its siren arrive more often because the speed of the vehicle makes them travel a bit faster. When the engine drives away from you, the vehicle's speed works the opposite way—making the sound waves travel slower and arrive less often. Therefore, you hear quite a noticeable drop in the siren's pitch at the exact moment when it passes by. This is called the Doppler effect.

The same science is at work in a radar speed gun. When a police officer fires a radar beam at your car, the metal bodywork reflects the beam straight back. Nevertheless, the faster your car is traveling, the more it will change the frequency of the radio waves in the beam. Sensitive electronic equipment in the radar gun uses this information to calculate how fast your car is going.

Radar has many scientific uses. Doppler radar is also used in weather forecasting to figure out how fast storms are moving and when they are likely to arrive in particular towns and cities. Effectively, the weather forecasters fire out radar beams into clouds and use the reflected beams to measure how quickly the rain is traveling and how fast it is falling. Scientists use a form of visible radar called LIDAR (light detection and ranging) to measure air pollution with lasers. Archeologists and geologists point radar down into the ground to study the composition of the Earth and find buried deposits of historical interest.

One place radar is not used is on board submarines. Electromagnetic waves do not travel readily through dense seawater (that is why it is dark in the deep ocean). Instead, submarines use a very similar system called SONAR (Sound Navigation And Ranging), which uses sound to "see" objects instead of radio waves.

Radar is extremely effective at spotting enemy aircraft and ships—so much so that military scientists had to develop some way around it! If you have a superb radar system, chances are your enemy has one too. If you can spot his airplanes, he can spot yours. Therefore, you really need airplanes that can somehow "hide" themselves inside the enemy's radar without being spotted. Stealth technology is designed to do just that. You may have seen the US air force's sinister-looking B2 stealth bomber. Its sharp, angular lines and metal-coated windows are designed to scatter or absorb beams of radio waves so enemy radar operators cannot detect them. A stealth airplane is so effective at doing this that it shows up on a radar screen with no more energy than a small bird!

Date: 2016-03-03; view: 877