How They Work

Radar is something that is in use all around us, although it is normally invisible. There are so many cases in which Radar can be put into use. Some of the most commonly heard of are in the use of radar to track planes both on the ground and in the air, and also to guide planes in for smooth landings. Police use radar to detect the speed of passing motorists. NASA uses radar to map the Earth and other planets, to track satellites and space debris and to help with things like docking and manoeuvring. The military uses it to detect the enemy and to guide weapons. Meteorologists use radar to track storms, hurricanes and tornadoes. You even see a form of radar at many grocery stores when the doors open automatically as you approach them! Obviously, radar is an extremely useful technology. When one talks of radar, many people jump to the obvious thought of its application in the military but that is just one or two of the applications. When people use radar, they are usually trying to accomplish one of the following; Detecting the presence of an object in a given path or distance, usually that object is moving, like an airplane, but radar can also be used to detect stationary objects buried underground. In some cases, radar can identify an object as well; for example, it can identify the type of aircraft it has detected. On the other hand, radar can detect the speed of an object that is the reason why police use radar to detect the speed of vehicles. That said and done, radar can also be used to map something; like the space shuttle and orbiting satellites use something called Synthetic Aperture Radar to create detailed topographic maps of the surface of planets and moons. All these applications can be accomplished using two things you may be familiar with from everyday life: echo and Doppler shift. These two concepts are easy to understand in the dominion of sound because your ears hear echo and Doppler shift every day. Radar makes use of the same techniques but using radio waves. Going by the sound principle, let us use it to denote the functionality of the same since you are already familiar with this concept. An echo is something you experience all the time. If you shout into a well or across a valley, the echo comes back a moment later. The echo occurs because some of the sound waves in your shout reflect off of a surface (either the water at the bottom of the well or the wall on the far side) and travel back to your ears. The length of time between the moment you shout and the moment that you hear the echo is determined by the distance between you and the surface that creates the echo. Now, the Doppler Shift is also common. You probably experience it daily (often without realizing it). Doppler shift occurs when sound is generated by, or reflected off of, a moving object. Doppler shift in the extreme creates sonic booms. The Doppler shift, let’s say there is a car coming toward you at 60 kph and its horn is blaring. You will hear the horn playing one “note” as the car approaches, but when the car passes you the sound of the horn will suddenly shift to a lower note. It’s the same horn making the same sound the whole time. The change you hear is caused by Doppler shift. (To be cont’d) eddie@afrowebs.com