Doppler Effect Statement : The Doppler effect, named after Austrian physicist J. C.Doppler who first described it for sound in 1842, states that“The waves emitted from a source moving toward an observerare squeezed; i.e. The waves wavelength is decreased andfrequency is increased,” as shown in the schematic below.Conversely, waves emitted from a source moving away froman observer are stretched; i.e. the waves wavelength isincreased and frequency is decreased. The waves can beacoustic waves or electro-magnetic radiation.
Laser Doppler Velocimeter: The laser Doppler velocimeter sends a monochromaticlaser beam toward the target and collects the reflectedradiation. According to the Doppler effect, the change inwavelength of the reflected radiation is a function of thetargeted objects relative velocity. Thus, the velocity of theobject can be obtained by measuring the change in wavelengthof the reflected laser light, which is done by forming aninterference fringe pattern (i.e. superimpose the original andreflected signals).