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The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. [ 1 ] [ 2 ] [ 3 ] The Doppler effect is named after the physicist Christian Doppler , who described the phenomenon in 1842.
The relativistic Doppler effect is the change in frequency, wavelength and amplitude [1] of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect, first proposed by Christian Doppler in 1842 [2]), when taking into account effects described by the special theory of relativity.
Early Doppler radars included CW, but these quickly led to the development of frequency modulated continuous wave radar, which sweeps the transmitter frequency to encode and determine range. With the advent of digital techniques, Pulse-Doppler radars (PD) became light enough for aircraft use, and Doppler processors for coherent pulse radars ...
Regardless, radars that employ the technique are universally coherent, with a very stable radio frequency, and the pulse packets may also be used to make measurements of the Doppler shift (a velocity-dependent modification of the apparent radio frequency), especially when the PRFs are in the hundreds-of-kilohertz range. Radars exploiting ...
Microwave Doppler frequency shift produced by reflector motion falls into the audible sound range for human beings (20–20 000 Hz), which is used for target classification in addition to the kinds of conventional radar display used for that purpose, like A-scope, B-scope, C-scope, and RHI indicator. The human ear may be able to tell the ...
This type of radar is typically used with competition sports, like golf, tennis, baseball, NASCAR racing, and some smart-home appliances including light-bulbs and motion sensors. The Doppler frequency change depends on the speed of light in the air (c’ ≈ c/1.0003 is slightly slower than in vacuum) and v the speed of the target: [4]
Only a single jet is visible in M87. Two jets are visible in 3C 31.. In physics, relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of light.
This range is sometimes called the fingerprint region, since the mid-infrared absorption spectrum of a compound is very specific for that compound. Near-infrared, from 120 THz to 400 THz (2,500–750 nm). Physical processes that are relevant for this range are similar to those for visible light.