![]() Since frequency is inversely proportional to wavelength, the frequency of the sinusoidal wave appears to have increased. This is because the target has moved closer in the interval of time between the previous and current wave crest.Īs long as this motion continues, the distance between the arriving wave crests is shorter than the distance between the transmitted wave crests. When this object is moving towards the radar system, the next wave crest reflected has a shorter round trip distance to travel, from the radar to the target and back to the radar. The distance from the crest of each wave to the next is the wavelength, which is inversely proportional to the frequency.Įach successive wave is reflected from the target object of interest. Consider the transmission of a sinusoidal wave. What happens in a radar system is that the pulse frequency is modified by the process of being reflected by a moving object. The relationship between wavelength and frequency is: Since the ground returns will be at the same range as the vehicle, the difference in velocity will be the means of discrimination. An example is airborne radar trying to track a moving vehicle on the ground. Doppler filtering can be used to discriminate between objects moving at different relative velocities. Doppler processing became possible with digital computers and today, nearly all radar systems incorporate Doppler processing.īy measuring the Doppler rate, the radar is able to measure the relative velocity of all objects returning echoes to the radar system – whether planes, vehicles, or ground features. The use of Doppler processing allows another characteristic of the return to be used – relative velocity. Measuring round trip return timing is fundamental to radar, but it can be difficult to distinguish returns from the target of interest and other objects or background located at similar distances.
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