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Radar pulsing causes a phenomenon called aliasing, which occurs when the Doppler frequency created by reflector motion exceeds the pulse repetition frequency (PRF). [1] This concept is related to range ambiguity resolution. Doppler frequency shift is introduced onto reflected signals used by radar.
That is, where () is the maximum Doppler spread or, maximum Doppler frequency or, maximum Doppler shift given by = with being the center frequency of the emitter. Coherence time is actually a statistical measure of the time duration over which the channel impulse response is essentially invariant, and quantifies the similarity of the channel ...
The magnitude of the shift is a function of the wavelength of the signal and the angular velocity of the antenna: S = r W / λ Where S is the Doppler shift in frequency (Hz), r is the radius of the circle, W is the angular velocity in radians per second, λ is the target wavelength and c is the speed of light in meters per second. [13]
Three common methods are used to calculate the Doppler shift and thus the water velocity along the acoustic beams. The first method uses a monochromatic transmit pulse and is referred to as "incoherent" or "narrowband". The method is robust and provides good quality mean current profiles but has limited space-time resolution.
Laser Doppler velocimetry, also known as laser Doppler anemometry, is the technique of using the Doppler shift in a laser beam to measure the velocity in transparent or semi-transparent fluid flows or the linear or vibratory motion of opaque, reflecting surfaces. The measurement with laser Doppler anemometry is absolute and linear with velocity ...
The frequency shift caused only by the electrophoresis of particles is equal to the apparent mobility at the stationary layer. The velocity of the electrophoretic migration thus obtained is proportional to the electric field as shown in Fig. 7. The frequency shift increases with increase of the scattering angle as shown in Fig. 8.
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Basic components of a laser Doppler vibrometer A laser Doppler vibrometer ( LDV ) is a scientific instrument that is used to make non-contact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the reflected ...