Speed Detection of Moving Vehicles Using Doppler Effect

2868 Words Mar 17th, 2012 12 Pages


Although there is good road safety performance the number of people killed and injured on our roads remain unacceptably high. So the roads safety strategy was published or introduced to support the new casualty reduction targets. The road safety strategy includes all forms of invention based on the engineering, education and enforcement and recognizes that there are many different factors that lead to traffic collisions and casualties. The main reason is speed of vehicle. We use traffic lights and other traffic manager to reduce the speed. One among them is speed cameras.
Speed cameras on the side of urban and rural roads, usually placed to catch
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Doppler Effect: the principle of this effect is well known in the study of sound. It is known that if the source of sound, emitting a note of frequency 'v' is move with a constant velocity 'V' relative to an observers, it is found that the observer ‘p’ perceives a sound having the frequency v' which differs from 'v', being greater or smaller according to the source is move towards or away from observers. This phenomenon in sound was first explained by Doppler and hence the name Doppler effect. But Fizeau showed that the same effect on light. Thus if the source of light is moving with a wavelength observed in the Spectroscope slightly different from the original wavelength.
The principle of speed camera that is the Doppler's effect can be described by the formula
fM = 2vfEcos(α/c)
fM if the frequency of the received signal
v is the speed of vehicles
fE if the frequency of transmitted signal
α is the angle between the transmitted signal and path along which the vehicle travels
c is propagation speed of the signal in the air.

Figure 1. The Doppler Effect
From this we can deduce that sending a fixed frequency signal towards the car and then measuring the efficiency of the returning signal the can the deduce the speed of the car.The principal used for Radar in speed camera, although they have little in common…