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Unformatted text preview: GENERAL INFORMATION: Radio detection and ranging, radar, is used to find the distance of an object, the velocity of an object, and is used to map terrain. Radar is used in navigation equipment, GPS, and weather forecasting. Also, radar is used as a military defense and assault weapon. Radar is accomplished by using the echo and Doppler shift of radio waves. Echo occurs when waves, usually sound waves, are reflected off of a distant object. For example, while a man named John hikes through the mountains, he shouts, “Hello.” John hears his own sound waves bouncing off of the mountains and returning to him. Doppler shift, however, is a much more intricate phenomenon. The Doppler Effect occurs when waves reflect off of a moving object. Doppler shift is the changing of frequency caused by the relative change in position of the source of the waves or the object reflecting the waves. For example, an observer is waiting at a railroad crossing for an oncoming train, one mile away, to pass. The train is not moving, just blowing its whistle. The sound waves travel at 600 miles per hour, to make calculation easier. If the train blows its whistle for one minute, the observer will hear nothing for six seconds and then will hear one minute of the whistle. Now let’s say that the train is moving at 60 miles per hour and again blows its whistle for exactly one minute. The observer will hear nothing for six seconds as sound travels to the cross station, but then the observer will only hear 54 seconds of sound. The reason for this is because as the car is moving, the sound waves are “stacking” upon one another. This creates a higher frequency of the sound and changes the tone based on the velocity of both the observer and the train. The opposite happens as soon as the train passes. The sound is lower because the train is moving away causing the frequency to lower compared to the resting position (How Radar Works). Using the equation f = f (1 – V 0 / V), where f is the observerd frequency, f is the actual frequency, V is the velocity of the waves, and V 0 is the speed of the source relative to the observer (negative if it is moving towards the observer), we can find the velocity of the source or the observer. This is the method used by radar detectors to determine the speed of an object (Morehouse)....
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- Spring '08
- Sir Robert Watson Watt