As long as this motion continues, the distance between the arriving wave crests is shorter than the distance between the transmitted wave crests. This is because the target has moved closer in the interval of time between the previous and current wave crest. When this object is moving toward 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. Each successive wave is reflected from the target object of interest. The distance from the crest of each wave to the next is the wavelength, which is inversely proportional to the frequency. Consider the transmission of a sinusoidal wave. What is happening in a radar system is that the frequency is modified by the process of being reflected by a moving object. Technically this is true only in a vacuum, but the effect of the medium such as our atmosphere can be ignored in radar discussions. The speed of light is constant-Einstein proved this.
/cloudfront-us-east-1.images.arcpublishing.com/gray/DU6SQ6RYSBF7DDRJRMZVN7Y5JU.jpg "doppler max 6")
Where f = wave frequency (Hz or cycles per second), λ = wavelength (meters), v = speed of light (approximately 3 × 10 8 m/s).
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