The Doppler principle in radar refers to the phenomenon where the frequency of radio waves changes when they are reflected off a moving object. Named after the Austrian physicist Christian Doppler, this principle states that if an object (such as an airplane or vehicle) moves toward or away from a radar transmitter/receiver, the frequency of the reflected waves will be shifted either higher or lower to that of the original transmitted frequency. This frequency shift, known as the Doppler shift, is directly proportional to the speed of the object and the frequency of the transmitted waves. Radar systems use this principle to measure the speed and direction of moving objects, which is crucial in applications such as weather monitoring, air traffic control and military surveillance.
The Doppler principle, as formulated by Christian Doppler, describes the perceived change in frequency of waves emitted by a moving source relative to an observer. This principle applies to various types of waves, including sound waves, light waves, and radio waves used in radar. In radar applications, the Doppler principle explains how the frequency of radar waves changes when they bounce off a moving object. If the object moves toward the radar transmitter/receiver, the reflected waves have a higher frequency (shorter wavelength) than the transmitted waves. Conversely, if the object moves away, the reflected waves have a lower frequency (longer wavelength). This frequency shift allows radar systems to detect the speed of moving objects, providing valuable information for navigation, surveillance and other applications.