Dictionary:Fig D-21

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FIG. D-21. (a) Doppler effect in observing a satellite. Along with knowledge of the satellite’s orbit, s, the time of closest approach of a satellite in near-polar orbit gives the latitude and the rate of change of frequency gives the longitude. The quantity measured is often the beat frequency (offset frequency) between the signal from the satellite and a reference frequency. (b) Doppler sonar uses four transducers to send sonar beams fore and aft and to each side, and to receive the reflections of these beams from the sea floor. The use of four beams allows the effects of the ship’s roll, pitch, and yaw to be reduced. The ship’s velocity is computed from the Doppler-effect frequency shift of the reflected beams. (Courtesy Marquardt, 1963.)