. Aerographer's Mate 3 & 2. United States. Navy; Meteorology; Oceanography. AEROGRAPHER'S MATE 3 & 2 change in frequency of a signal resulting from relative motion between the source and the receiver is known as doppler effect. Figure 12-25 illustrates doppler effect. Each sound wave produced by the whistle is given an extra "push" by the motion of the train. As the train comes toward you, the resultant effect is an increase in pitch, caused by compression of the waves. As the train moves away from you, the sound waves are spread further apart, resulting in a lower pitch. Bec
. Aerographer's Mate 3 & 2. United States. Navy; Meteorology; Oceanography. AEROGRAPHER'S MATE 3 & 2 change in frequency of a signal resulting from relative motion between the source and the receiver is known as doppler effect. Figure 12-25 illustrates doppler effect. Each sound wave produced by the whistle is given an extra "push" by the motion of the train. As the train comes toward you, the resultant effect is an increase in pitch, caused by compression of the waves. As the train moves away from you, the sound waves are spread further apart, resulting in a lower pitch. Because doppler effect varies inversely with the velocity of sound, the effect is much less marked in the sea than it is in the air. LOW HIGH. Figure 12-25. —Doppler effect. APPLICATION OF SOUND IN SONAR OPERATION One of the primary applications of knowl- edge of sound characteristics is in SONAR operations. SONAR is an acronym for Sound Navigation and Ranging, Sound is used in SONAR operations in one of two basic ways: active ranging and passive ranging. In passive sonar operations, sound generated by a submarine target is detected and evaluated by an antisubmarine unit, such as a destroyer. By applying the doppler principle, a sonar operator can determine if the submarine is closing or moving away from the destroyer. In active operation the destroyer sends out a package of sound waves (pulses), which will reflect or bounce from the submarine. By knowing the direction the sound travels, the sonarman can determine the target bearing. A measure of the time required for the sound pulse to reach the target and return gives an indication of the range to the submarine. To effectively use SONAR for submarine detection, the sonar operator must make maxi- mum use of the various properties of sound discussed previously. Any sound the sonar detector hears that is not part of the sound package from the target is interference. The major source of interference in sonar operations is b
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