A License Plate Recognition and Speed Detection System - Index of

Fig. 17 Doppler Effect (Ref. 14)
The Austrian physicist Christian Andreas Doppler first described the Doppler Effect � in
1842. He noticed how the frequency of a sound wave changed as the emitting object moved
toward or away from a stationary listener. When the emitting object was coming toward the
listener, the pitch or frequency of the sound increased. But as the object moved away from the
listener, the pitch decreased. The largest Doppler Effect is heard when the source is moving
directly toward or away from the listener. The frequency heard by the listener can be calculated
from the following equation:
fL = [(v + vL)/(v + vS)] fS (Eq. 1)
where: fL is the frequency heard by the listener
fS is the frequency emitted by the source
� Different sources have differing names for Dr. Doppler. On a NASA website, he is Johann Christian Doppler.
Webster’s Dictionary has him simply as C.J. Doppler. Wikipedia gives his name as Christian Andreas Doppler
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